1 # SPDX-License-Identifier: GPL-2.0+
3 # (C) Copyright 2000 - 2013
4 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
9 This directory contains the source code for U-Boot, a boot loader for
10 Embedded boards based on PowerPC, ARM, MIPS and several other
11 processors, which can be installed in a boot ROM and used to
12 initialize and test the hardware or to download and run application
15 The development of U-Boot is closely related to Linux: some parts of
16 the source code originate in the Linux source tree, we have some
17 header files in common, and special provision has been made to
18 support booting of Linux images.
20 Some attention has been paid to make this software easily
21 configurable and extendable. For instance, all monitor commands are
22 implemented with the same call interface, so that it's very easy to
23 add new commands. Also, instead of permanently adding rarely used
24 code (for instance hardware test utilities) to the monitor, you can
25 load and run it dynamically.
31 In general, all boards for which a default configuration file exists in the
32 configs/ directory have been tested to some extent and can be considered
33 "working". In fact, many of them are used in production systems.
35 In case of problems you can use
37 scripts/get_maintainer.pl <path>
39 to identify the people or companies responsible for various boards and
40 subsystems. Or have a look at the git log.
46 In case you have questions about, problems with or contributions for
47 U-Boot, you should send a message to the U-Boot mailing list at
48 <u-boot@lists.denx.de>. There is also an archive of previous traffic
49 on the mailing list - please search the archive before asking FAQ's.
50 Please see https://lists.denx.de/pipermail/u-boot and
51 https://marc.info/?l=u-boot
53 Where to get source code:
54 =========================
56 The U-Boot source code is maintained in the Git repository at
57 https://source.denx.de/u-boot/u-boot.git ; you can browse it online at
58 https://source.denx.de/u-boot/u-boot
60 The "Tags" links on this page allow you to download tarballs of
61 any version you might be interested in. Official releases are also
62 available from the DENX file server through HTTPS or FTP.
63 https://ftp.denx.de/pub/u-boot/
64 ftp://ftp.denx.de/pub/u-boot/
70 - start from 8xxrom sources
71 - create PPCBoot project (https://sourceforge.net/projects/ppcboot)
73 - make it easier to add custom boards
74 - make it possible to add other [PowerPC] CPUs
75 - extend functions, especially:
76 * Provide extended interface to Linux boot loader
79 * ATA disk / SCSI ... boot
80 - create ARMBoot project (https://sourceforge.net/projects/armboot)
81 - add other CPU families (starting with ARM)
82 - create U-Boot project (https://sourceforge.net/projects/u-boot)
83 - current project page: see https://www.denx.de/wiki/U-Boot
89 The "official" name of this project is "Das U-Boot". The spelling
90 "U-Boot" shall be used in all written text (documentation, comments
91 in source files etc.). Example:
93 This is the README file for the U-Boot project.
95 File names etc. shall be based on the string "u-boot". Examples:
97 include/asm-ppc/u-boot.h
99 #include <asm/u-boot.h>
101 Variable names, preprocessor constants etc. shall be either based on
102 the string "u_boot" or on "U_BOOT". Example:
104 U_BOOT_VERSION u_boot_logo
105 IH_OS_U_BOOT u_boot_hush_start
111 Starting with the release in October 2008, the names of the releases
112 were changed from numerical release numbers without deeper meaning
113 into a time stamp based numbering. Regular releases are identified by
114 names consisting of the calendar year and month of the release date.
115 Additional fields (if present) indicate release candidates or bug fix
116 releases in "stable" maintenance trees.
119 U-Boot v2009.11 - Release November 2009
120 U-Boot v2009.11.1 - Release 1 in version November 2009 stable tree
121 U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release
127 /arch Architecture-specific files
128 /arc Files generic to ARC architecture
129 /arm Files generic to ARM architecture
130 /m68k Files generic to m68k architecture
131 /microblaze Files generic to microblaze architecture
132 /mips Files generic to MIPS architecture
133 /nios2 Files generic to Altera NIOS2 architecture
134 /powerpc Files generic to PowerPC architecture
135 /riscv Files generic to RISC-V architecture
136 /sandbox Files generic to HW-independent "sandbox"
137 /sh Files generic to SH architecture
138 /x86 Files generic to x86 architecture
139 /xtensa Files generic to Xtensa architecture
140 /api Machine/arch-independent API for external apps
141 /board Board-dependent files
142 /boot Support for images and booting
143 /cmd U-Boot commands functions
144 /common Misc architecture-independent functions
145 /configs Board default configuration files
146 /disk Code for disk drive partition handling
147 /doc Documentation (a mix of ReST and READMEs)
148 /drivers Device drivers
149 /dts Makefile for building internal U-Boot fdt.
150 /env Environment support
151 /examples Example code for standalone applications, etc.
152 /fs Filesystem code (cramfs, ext2, jffs2, etc.)
153 /include Header Files
154 /lib Library routines generic to all architectures
155 /Licenses Various license files
157 /post Power On Self Test
158 /scripts Various build scripts and Makefiles
159 /test Various unit test files
160 /tools Tools to build and sign FIT images, etc.
162 Software Configuration:
163 =======================
165 Selection of Processor Architecture and Board Type:
166 ---------------------------------------------------
168 For all supported boards there are ready-to-use default
169 configurations available; just type "make <board_name>_defconfig".
171 Example: For a TQM823L module type:
174 make TQM823L_defconfig
176 Note: If you're looking for the default configuration file for a board
177 you're sure used to be there but is now missing, check the file
178 doc/README.scrapyard for a list of no longer supported boards.
183 U-Boot can be built natively to run on a Linux host using the 'sandbox'
184 board. This allows feature development which is not board- or architecture-
185 specific to be undertaken on a native platform. The sandbox is also used to
186 run some of U-Boot's tests.
188 See doc/arch/sandbox/sandbox.rst for more details.
191 Board Initialisation Flow:
192 --------------------------
194 This is the intended start-up flow for boards. This should apply for both
195 SPL and U-Boot proper (i.e. they both follow the same rules).
197 Note: "SPL" stands for "Secondary Program Loader," which is explained in
198 more detail later in this file.
200 At present, SPL mostly uses a separate code path, but the function names
201 and roles of each function are the same. Some boards or architectures
202 may not conform to this. At least most ARM boards which use
203 CONFIG_SPL_FRAMEWORK conform to this.
205 Execution typically starts with an architecture-specific (and possibly
206 CPU-specific) start.S file, such as:
208 - arch/arm/cpu/armv7/start.S
209 - arch/powerpc/cpu/mpc83xx/start.S
210 - arch/mips/cpu/start.S
212 and so on. From there, three functions are called; the purpose and
213 limitations of each of these functions are described below.
216 - purpose: essential init to permit execution to reach board_init_f()
217 - no global_data or BSS
218 - there is no stack (ARMv7 may have one but it will soon be removed)
219 - must not set up SDRAM or use console
220 - must only do the bare minimum to allow execution to continue to
222 - this is almost never needed
223 - return normally from this function
226 - purpose: set up the machine ready for running board_init_r():
227 i.e. SDRAM and serial UART
228 - global_data is available
230 - BSS is not available, so you cannot use global/static variables,
231 only stack variables and global_data
233 Non-SPL-specific notes:
234 - dram_init() is called to set up DRAM. If already done in SPL this
238 - you can override the entire board_init_f() function with your own
240 - preloader_console_init() can be called here in extremis
241 - should set up SDRAM, and anything needed to make the UART work
242 - there is no need to clear BSS, it will be done by crt0.S
243 - for specific scenarios on certain architectures an early BSS *can*
244 be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
245 of BSS prior to entering board_init_f()) but doing so is discouraged.
246 Instead it is strongly recommended to architect any code changes
247 or additions such to not depend on the availability of BSS during
248 board_init_f() as indicated in other sections of this README to
249 maintain compatibility and consistency across the entire code base.
250 - must return normally from this function (don't call board_init_r()
253 Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
254 this point the stack and global_data are relocated to below
255 CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
259 - purpose: main execution, common code
260 - global_data is available
262 - BSS is available, all static/global variables can be used
263 - execution eventually continues to main_loop()
265 Non-SPL-specific notes:
266 - U-Boot is relocated to the top of memory and is now running from
270 - stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
271 CONFIG_SYS_FSL_HAS_CCI400
273 Defined For SoC that has cache coherent interconnect
276 CONFIG_SYS_FSL_HAS_CCN504
278 Defined for SoC that has cache coherent interconnect CCN-504
280 The following options need to be configured:
282 - CPU Type: Define exactly one, e.g. CONFIG_MPC85XX.
284 - Board Type: Define exactly one, e.g. CONFIG_MPC8540ADS.
289 Specifies that the core is a 64-bit PowerPC implementation (implements
290 the "64" category of the Power ISA). This is necessary for ePAPR
291 compliance, among other possible reasons.
293 CONFIG_SYS_FSL_ERRATUM_A004510
295 Enables a workaround for erratum A004510. If set,
296 then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
297 CFG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
299 CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
300 CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
302 Defines one or two SoC revisions (low 8 bits of SVR)
303 for which the A004510 workaround should be applied.
305 The rest of SVR is either not relevant to the decision
306 of whether the erratum is present (e.g. p2040 versus
307 p2041) or is implied by the build target, which controls
308 whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
310 See Freescale App Note 4493 for more information about
313 CFG_SYS_FSL_CORENET_SNOOPVEC_COREONLY
315 This is the value to write into CCSR offset 0x18600
316 according to the A004510 workaround.
318 CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
319 Single Source Clock is clocking mode present in some of FSL SoC's.
320 In this mode, a single differential clock is used to supply
321 clocks to the sysclock, ddrclock and usbclock.
323 - Generic CPU options:
326 Freescale DDR driver in use. This type of DDR controller is
327 found in mpc83xx, mpc85xx as well as some ARM core SoCs.
330 Freescale DDR memory-mapped register base.
332 CONFIG_SYS_FSL_IFC_CLK_DIV
333 Defines divider of platform clock(clock input to IFC controller).
335 CONFIG_SYS_FSL_LBC_CLK_DIV
336 Defines divider of platform clock(clock input to eLBC controller).
338 CFG_SYS_FSL_DDR_SDRAM_BASE_PHY
339 Physical address from the view of DDR controllers. It is the
340 same as CFG_SYS_DDR_SDRAM_BASE for all Power SoCs. But
341 it could be different for ARM SoCs.
344 CONFIG_XWAY_SWAP_BYTES
346 Enable compilation of tools/xway-swap-bytes needed for Lantiq
347 XWAY SoCs for booting from NOR flash. The U-Boot image needs to
348 be swapped if a flash programmer is used.
351 CFG_SYS_EXCEPTION_VECTORS_HIGH
353 Select high exception vectors of the ARM core, e.g., do not
354 clear the V bit of the c1 register of CP15.
357 Generic timer clock source frequency.
359 COUNTER_FREQUENCY_REAL
360 Generic timer clock source frequency if the real clock is
361 different from COUNTER_FREQUENCY, and can only be determined
365 CONFIG_TEGRA_SUPPORT_NON_SECURE
367 Support executing U-Boot in non-secure (NS) mode. Certain
368 impossible actions will be skipped if the CPU is in NS mode,
369 such as ARM architectural timer initialization.
371 - Linux Kernel Interface:
374 New kernel versions are expecting firmware settings to be
375 passed using flattened device trees (based on open firmware
379 * New libfdt-based support
380 * Adds the "fdt" command
381 * The bootm command automatically updates the fdt
383 OF_TBCLK - The timebase frequency.
385 boards with QUICC Engines require OF_QE to set UCC MAC
390 U-Boot can detect if an IDE device is present or not.
391 If not, and this new config option is activated, U-Boot
392 removes the ATA node from the DTS before booting Linux,
393 so the Linux IDE driver does not probe the device and
394 crash. This is needed for buggy hardware (uc101) where
395 no pull down resistor is connected to the signal IDE5V_DD7.
397 - vxWorks boot parameters:
399 bootvx constructs a valid bootline using the following
400 environments variables: bootdev, bootfile, ipaddr, netmask,
401 serverip, gatewayip, hostname, othbootargs.
402 It loads the vxWorks image pointed bootfile.
404 Note: If a "bootargs" environment is defined, it will override
405 the defaults discussed just above.
407 - Cache Configuration for ARM:
408 CFG_SYS_PL310_BASE - Physical base address of PL310
409 controller register space
414 If you have Amba PrimeCell PL011 UARTs, set this variable to
415 the clock speed of the UARTs.
419 If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
420 define this to a list of base addresses for each (supported)
421 port. See e.g. include/configs/versatile.h
423 CONFIG_SERIAL_HW_FLOW_CONTROL
425 Define this variable to enable hw flow control in serial driver.
426 Current user of this option is drivers/serial/nsl16550.c driver
428 - Removal of commands
429 If no commands are needed to boot, you can disable
430 CONFIG_CMDLINE to remove them. In this case, the command line
431 will not be available, and when U-Boot wants to execute the
432 boot command (on start-up) it will call board_run_command()
433 instead. This can reduce image size significantly for very
434 simple boot procedures.
436 - Regular expression support:
438 If this variable is defined, U-Boot is linked against
439 the SLRE (Super Light Regular Expression) library,
440 which adds regex support to some commands, as for
441 example "env grep" and "setexpr".
444 CFG_SYS_WATCHDOG_FREQ
445 Some platforms automatically call WATCHDOG_RESET()
446 from the timer interrupt handler every
447 CFG_SYS_WATCHDOG_FREQ interrupts. If not set by the
448 board configuration file, a default of CONFIG_SYS_HZ/2
449 (i.e. 500) is used. Setting CFG_SYS_WATCHDOG_FREQ
450 to 0 disables calling WATCHDOG_RESET() from the timer
454 The CFG_SYS_I2C_PCA953X_WIDTH option specifies a list of
455 chip-ngpio pairs that tell the PCA953X driver the number of
456 pins supported by a particular chip.
458 Note that if the GPIO device uses I2C, then the I2C interface
459 must also be configured. See I2C Support, below.
462 When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
463 accesses and can checksum them or write a list of them out
464 to memory. See the 'iotrace' command for details. This is
465 useful for testing device drivers since it can confirm that
466 the driver behaves the same way before and after a code
467 change. Currently this is supported on sandbox and arm. To
468 add support for your architecture, add '#include <iotrace.h>'
469 to the bottom of arch/<arch>/include/asm/io.h and test.
471 Example output from the 'iotrace stats' command is below.
472 Note that if the trace buffer is exhausted, the checksum will
473 still continue to operate.
476 Start: 10000000 (buffer start address)
477 Size: 00010000 (buffer size)
478 Offset: 00000120 (current buffer offset)
479 Output: 10000120 (start + offset)
480 Count: 00000018 (number of trace records)
481 CRC32: 9526fb66 (CRC32 of all trace records)
485 When CONFIG_TIMESTAMP is selected, the timestamp
486 (date and time) of an image is printed by image
487 commands like bootm or iminfo. This option is
488 automatically enabled when you select CONFIG_CMD_DATE .
490 - Partition Labels (disklabels) Supported:
491 Zero or more of the following:
492 CONFIG_MAC_PARTITION Apple's MacOS partition table.
493 CONFIG_ISO_PARTITION ISO partition table, used on CDROM etc.
494 CONFIG_EFI_PARTITION GPT partition table, common when EFI is the
495 bootloader. Note 2TB partition limit; see
497 CONFIG_SCSI) you must configure support for at
498 least one non-MTD partition type as well.
500 - NETWORK Support (PCI):
502 Utility code for direct access to the SPI bus on Intel 8257x.
503 This does not do anything useful unless you set at least one
504 of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.
507 Support for National dp83815 chips.
510 Support for National dp8382[01] gigabit chips.
512 - NETWORK Support (other):
514 Support for the Calxeda XGMAC device
517 Support for SMSC's LAN91C96 chips.
519 CONFIG_LAN91C96_USE_32_BIT
520 Define this to enable 32 bit addressing
522 CFG_SYS_DAVINCI_EMAC_PHY_COUNT
523 Define this if you have more then 3 PHYs.
526 Support for Faraday's FTGMAC100 Gigabit SoC Ethernet
528 CONFIG_FTGMAC100_EGIGA
529 Define this to use GE link update with gigabit PHY.
530 Define this if FTGMAC100 is connected to gigabit PHY.
531 If your system has 10/100 PHY only, it might not occur
532 wrong behavior. Because PHY usually return timeout or
533 useless data when polling gigabit status and gigabit
534 control registers. This behavior won't affect the
535 correctnessof 10/100 link speed update.
538 Support for Renesas on-chip Ethernet controller
540 CFG_SH_ETHER_USE_PORT
541 Define the number of ports to be used
543 CFG_SH_ETHER_PHY_ADDR
544 Define the ETH PHY's address
546 CFG_SH_ETHER_CACHE_WRITEBACK
547 If this option is set, the driver enables cache flush.
553 CONFIG_TPM_TIS_INFINEON
554 Support for Infineon i2c bus TPM devices. Only one device
555 per system is supported at this time.
557 CONFIG_TPM_TIS_I2C_BURST_LIMITATION
558 Define the burst count bytes upper limit
561 Support for STMicroelectronics TPM devices. Requires DM_TPM support.
563 CONFIG_TPM_ST33ZP24_I2C
564 Support for STMicroelectronics ST33ZP24 I2C devices.
565 Requires TPM_ST33ZP24 and I2C.
567 CONFIG_TPM_ST33ZP24_SPI
568 Support for STMicroelectronics ST33ZP24 SPI devices.
569 Requires TPM_ST33ZP24 and SPI.
572 Support for Atmel TWI TPM device. Requires I2C support.
575 Support for generic parallel port TPM devices. Only one device
576 per system is supported at this time.
579 Define this to enable the TPM support library which provides
580 functional interfaces to some TPM commands.
581 Requires support for a TPM device.
583 CONFIG_TPM_AUTH_SESSIONS
584 Define this to enable authorized functions in the TPM library.
585 Requires CONFIG_TPM and CONFIG_SHA1.
588 At the moment only the UHCI host controller is
589 supported (PIP405, MIP405); define
590 CONFIG_USB_UHCI to enable it.
591 define CONFIG_USB_KEYBOARD to enable the USB Keyboard
592 and define CONFIG_USB_STORAGE to enable the USB
595 Supported are USB Keyboards and USB Floppy drives
598 CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
602 Define the below if you wish to use the USB console.
603 Once firmware is rebuilt from a serial console issue the
604 command "setenv stdin usbtty; setenv stdout usbtty" and
605 attach your USB cable. The Unix command "dmesg" should print
606 it has found a new device. The environment variable usbtty
607 can be set to gserial or cdc_acm to enable your device to
608 appear to a USB host as a Linux gserial device or a
609 Common Device Class Abstract Control Model serial device.
610 If you select usbtty = gserial you should be able to enumerate
612 # modprobe usbserial vendor=0xVendorID product=0xProductID
613 else if using cdc_acm, simply setting the environment
614 variable usbtty to be cdc_acm should suffice. The following
615 might be defined in YourBoardName.h
617 If you have a USB-IF assigned VendorID then you may wish to
618 define your own vendor specific values either in BoardName.h
619 or directly in usbd_vendor_info.h. If you don't define
620 CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
621 CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
622 should pretend to be a Linux device to it's target host.
624 CONFIG_USBD_MANUFACTURER
625 Define this string as the name of your company for
626 - CONFIG_USBD_MANUFACTURER "my company"
628 CONFIG_USBD_PRODUCT_NAME
629 Define this string as the name of your product
630 - CONFIG_USBD_PRODUCT_NAME "acme usb device"
633 Define this as your assigned Vendor ID from the USB
634 Implementors Forum. This *must* be a genuine Vendor ID
635 to avoid polluting the USB namespace.
636 - CONFIG_USBD_VENDORID 0xFFFF
638 CONFIG_USBD_PRODUCTID
639 Define this as the unique Product ID
641 - CONFIG_USBD_PRODUCTID 0xFFFF
643 - ULPI Layer Support:
644 The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
645 the generic ULPI layer. The generic layer accesses the ULPI PHY
646 via the platform viewport, so you need both the genric layer and
647 the viewport enabled. Currently only Chipidea/ARC based
648 viewport is supported.
649 To enable the ULPI layer support, define CONFIG_USB_ULPI and
650 CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
651 If your ULPI phy needs a different reference clock than the
652 standard 24 MHz then you have to define CFG_ULPI_REF_CLK to
653 the appropriate value in Hz.
657 Support for Renesas on-chip MMCIF controller
660 Define the base address of MMCIF registers
663 Define the clock frequency for MMCIF
665 - USB Device Firmware Update (DFU) class support:
667 This enables the USB portion of the DFU USB class
670 This enables support for exposing NAND devices via DFU.
673 This enables support for exposing RAM via DFU.
674 Note: DFU spec refer to non-volatile memory usage, but
675 allow usages beyond the scope of spec - here RAM usage,
676 one that would help mostly the developer.
678 CONFIG_SYS_DFU_DATA_BUF_SIZE
679 Dfu transfer uses a buffer before writing data to the
680 raw storage device. Make the size (in bytes) of this buffer
681 configurable. The size of this buffer is also configurable
682 through the "dfu_bufsiz" environment variable.
684 CONFIG_SYS_DFU_MAX_FILE_SIZE
685 When updating files rather than the raw storage device,
686 we use a static buffer to copy the file into and then write
687 the buffer once we've been given the whole file. Define
688 this to the maximum filesize (in bytes) for the buffer.
689 Default is 4 MiB if undefined.
691 DFU_DEFAULT_POLL_TIMEOUT
692 Poll timeout [ms], is the timeout a device can send to the
693 host. The host must wait for this timeout before sending
694 a subsequent DFU_GET_STATUS request to the device.
696 DFU_MANIFEST_POLL_TIMEOUT
697 Poll timeout [ms], which the device sends to the host when
698 entering dfuMANIFEST state. Host waits this timeout, before
699 sending again an USB request to the device.
702 See Kconfig help for available keyboard drivers.
705 CONFIG_PHY_CLOCK_FREQ (ppc4xx)
707 The clock frequency of the MII bus
709 CONFIG_PHY_CMD_DELAY (ppc4xx)
711 Some PHY like Intel LXT971A need extra delay after
712 command issued before MII status register can be read
714 - BOOTP Recovery Mode:
715 CONFIG_BOOTP_RANDOM_DELAY
717 If you have many targets in a network that try to
718 boot using BOOTP, you may want to avoid that all
719 systems send out BOOTP requests at precisely the same
720 moment (which would happen for instance at recovery
721 from a power failure, when all systems will try to
722 boot, thus flooding the BOOTP server. Defining
723 CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
724 inserted before sending out BOOTP requests. The
725 following delays are inserted then:
727 1st BOOTP request: delay 0 ... 1 sec
728 2nd BOOTP request: delay 0 ... 2 sec
729 3rd BOOTP request: delay 0 ... 4 sec
731 BOOTP requests: delay 0 ... 8 sec
733 CFG_BOOTP_ID_CACHE_SIZE
735 BOOTP packets are uniquely identified using a 32-bit ID. The
736 server will copy the ID from client requests to responses and
737 U-Boot will use this to determine if it is the destination of
738 an incoming response. Some servers will check that addresses
739 aren't in use before handing them out (usually using an ARP
740 ping) and therefore take up to a few hundred milliseconds to
741 respond. Network congestion may also influence the time it
742 takes for a response to make it back to the client. If that
743 time is too long, U-Boot will retransmit requests. In order
744 to allow earlier responses to still be accepted after these
745 retransmissions, U-Boot's BOOTP client keeps a small cache of
746 IDs. The CFG_BOOTP_ID_CACHE_SIZE controls the size of this
747 cache. The default is to keep IDs for up to four outstanding
748 requests. Increasing this will allow U-Boot to accept offers
749 from a BOOTP client in networks with unusually high latency.
751 - DHCP Advanced Options:
753 - Link-local IP address negotiation:
754 Negotiate with other link-local clients on the local network
755 for an address that doesn't require explicit configuration.
756 This is especially useful if a DHCP server cannot be guaranteed
757 to exist in all environments that the device must operate.
759 See doc/README.link-local for more information.
761 - MAC address from environment variables
763 FDT_SEQ_MACADDR_FROM_ENV
765 Fix-up device tree with MAC addresses fetched sequentially from
766 environment variables. This config work on assumption that
767 non-usable ethernet node of device-tree are either not present
768 or their status has been marked as "disabled".
773 The device id used in CDP trigger frames.
775 CONFIG_CDP_DEVICE_ID_PREFIX
777 A two character string which is prefixed to the MAC address
782 A printf format string which contains the ascii name of
783 the port. Normally is set to "eth%d" which sets
784 eth0 for the first Ethernet, eth1 for the second etc.
786 CONFIG_CDP_CAPABILITIES
788 A 32bit integer which indicates the device capabilities;
789 0x00000010 for a normal host which does not forwards.
793 An ascii string containing the version of the software.
797 An ascii string containing the name of the platform.
801 A 32bit integer sent on the trigger.
803 CONFIG_CDP_POWER_CONSUMPTION
805 A 16bit integer containing the power consumption of the
806 device in .1 of milliwatts.
808 CONFIG_CDP_APPLIANCE_VLAN_TYPE
810 A byte containing the id of the VLAN.
812 - Status LED: CONFIG_LED_STATUS
814 Several configurations allow to display the current
815 status using a LED. For instance, the LED will blink
816 fast while running U-Boot code, stop blinking as
817 soon as a reply to a BOOTP request was received, and
818 start blinking slow once the Linux kernel is running
819 (supported by a status LED driver in the Linux
820 kernel). Defining CONFIG_LED_STATUS enables this
825 CONFIG_LED_STATUS_GPIO
826 The status LED can be connected to a GPIO pin.
827 In such cases, the gpio_led driver can be used as a
828 status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
829 to include the gpio_led driver in the U-Boot binary.
831 CFG_GPIO_LED_INVERTED_TABLE
832 Some GPIO connected LEDs may have inverted polarity in which
833 case the GPIO high value corresponds to LED off state and
834 GPIO low value corresponds to LED on state.
835 In such cases CFG_GPIO_LED_INVERTED_TABLE may be defined
836 with a list of GPIO LEDs that have inverted polarity.
839 CFG_SYS_NUM_I2C_BUSES
840 Hold the number of i2c buses you want to use.
842 CFG_SYS_I2C_DIRECT_BUS
843 define this, if you don't use i2c muxes on your hardware.
844 if CFG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
848 define how many muxes are maximal consecutively connected
849 on one i2c bus. If you not use i2c muxes, omit this
853 hold a list of buses you want to use, only used if
854 CFG_SYS_I2C_DIRECT_BUS is not defined, for example
855 a board with CFG_SYS_I2C_MAX_HOPS = 1 and
856 CFG_SYS_NUM_I2C_BUSES = 9:
858 CFG_SYS_I2C_BUSES {{0, {I2C_NULL_HOP}}, \
859 {0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
860 {0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
861 {0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
862 {0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
863 {0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
864 {1, {I2C_NULL_HOP}}, \
865 {1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
866 {1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
870 bus 0 on adapter 0 without a mux
871 bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
872 bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
873 bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
874 bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
875 bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
876 bus 6 on adapter 1 without a mux
877 bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
878 bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2
880 If you do not have i2c muxes on your board, omit this define.
882 - Legacy I2C Support:
883 If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
884 then the following macros need to be defined (examples are
885 from include/configs/lwmon.h):
889 (Optional). Any commands necessary to enable the I2C
890 controller or configure ports.
892 eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |= PB_SCL)
896 The code necessary to make the I2C data line active
897 (driven). If the data line is open collector, this
900 eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |= PB_SDA)
904 The code necessary to make the I2C data line tri-stated
905 (inactive). If the data line is open collector, this
908 eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)
912 Code that returns true if the I2C data line is high,
915 eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)
919 If <bit> is true, sets the I2C data line high. If it
920 is false, it clears it (low).
922 eg: #define I2C_SDA(bit) \
923 if(bit) immr->im_cpm.cp_pbdat |= PB_SDA; \
924 else immr->im_cpm.cp_pbdat &= ~PB_SDA
928 If <bit> is true, sets the I2C clock line high. If it
929 is false, it clears it (low).
931 eg: #define I2C_SCL(bit) \
932 if(bit) immr->im_cpm.cp_pbdat |= PB_SCL; \
933 else immr->im_cpm.cp_pbdat &= ~PB_SCL
937 This delay is invoked four times per clock cycle so this
938 controls the rate of data transfer. The data rate thus
939 is 1 / (I2C_DELAY * 4). Often defined to be something
942 #define I2C_DELAY udelay(2)
944 CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
946 If your arch supports the generic GPIO framework (asm/gpio.h),
947 then you may alternatively define the two GPIOs that are to be
948 used as SCL / SDA. Any of the previous I2C_xxx macros will
949 have GPIO-based defaults assigned to them as appropriate.
951 You should define these to the GPIO value as given directly to
952 the generic GPIO functions.
956 This option allows the use of multiple I2C buses, each of which
957 must have a controller. At any point in time, only one bus is
958 active. To switch to a different bus, use the 'i2c dev' command.
959 Note that bus numbering is zero-based.
963 This option specifies a list of I2C devices that will be skipped
964 when the 'i2c probe' command is issued.
967 #define CFG_SYS_I2C_NOPROBES {0x50,0x68}
969 will skip addresses 0x50 and 0x68 on a board with one I2C bus
973 If defined, then this indicates the I2C bus number for the RTC.
974 If not defined, then U-Boot assumes that RTC is on I2C bus 0.
976 CONFIG_SOFT_I2C_READ_REPEATED_START
978 defining this will force the i2c_read() function in
979 the soft_i2c driver to perform an I2C repeated start
980 between writing the address pointer and reading the
981 data. If this define is omitted the default behaviour
982 of doing a stop-start sequence will be used. Most I2C
983 devices can use either method, but some require one or
986 - SPI Support: CONFIG_SPI
988 Enables SPI driver (so far only tested with
989 SPI EEPROM, also an instance works with Crystal A/D and
990 D/As on the SACSng board)
993 Timeout for waiting until spi transfer completed.
994 default: (CONFIG_SYS_HZ/100) /* 10 ms */
996 - FPGA Support: CONFIG_FPGA
998 Enables FPGA subsystem.
1000 CONFIG_FPGA_<vendor>
1002 Enables support for specific chip vendors.
1005 CONFIG_FPGA_<family>
1007 Enables support for FPGA family.
1008 (SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
1010 CONFIG_SYS_FPGA_CHECK_BUSY
1012 Enable checks on FPGA configuration interface busy
1013 status by the configuration function. This option
1014 will require a board or device specific function to
1019 If defined, a function that provides delays in the FPGA
1020 configuration driver.
1022 CFG_SYS_FPGA_CHECK_ERROR
1024 Check for configuration errors during FPGA bitfile
1025 loading. For example, abort during Virtex II
1026 configuration if the INIT_B line goes low (which
1027 indicated a CRC error).
1029 CFG_SYS_FPGA_WAIT_INIT
1031 Maximum time to wait for the INIT_B line to de-assert
1032 after PROB_B has been de-asserted during a Virtex II
1033 FPGA configuration sequence. The default time is 500
1036 CFG_SYS_FPGA_WAIT_BUSY
1038 Maximum time to wait for BUSY to de-assert during
1039 Virtex II FPGA configuration. The default is 5 ms.
1041 CFG_SYS_FPGA_WAIT_CONFIG
1043 Time to wait after FPGA configuration. The default is
1046 - Vendor Parameter Protection:
1048 U-Boot considers the values of the environment
1049 variables "serial#" (Board Serial Number) and
1050 "ethaddr" (Ethernet Address) to be parameters that
1051 are set once by the board vendor / manufacturer, and
1052 protects these variables from casual modification by
1053 the user. Once set, these variables are read-only,
1054 and write or delete attempts are rejected. You can
1055 change this behaviour:
1057 If CONFIG_ENV_OVERWRITE is #defined in your config
1058 file, the write protection for vendor parameters is
1059 completely disabled. Anybody can change or delete
1062 The same can be accomplished in a more flexible way
1063 for any variable by configuring the type of access
1064 to allow for those variables in the ".flags" variable
1065 or define CFG_ENV_FLAGS_LIST_STATIC.
1070 Define this variable to enable the reservation of
1071 "protected RAM", i. e. RAM which is not overwritten
1072 by U-Boot. Define CFG_PRAM to hold the number of
1073 kB you want to reserve for pRAM. You can overwrite
1074 this default value by defining an environment
1075 variable "pram" to the number of kB you want to
1076 reserve. Note that the board info structure will
1077 still show the full amount of RAM. If pRAM is
1078 reserved, a new environment variable "mem" will
1079 automatically be defined to hold the amount of
1080 remaining RAM in a form that can be passed as boot
1081 argument to Linux, for instance like that:
1083 setenv bootargs ... mem=\${mem}
1086 This way you can tell Linux not to use this memory,
1087 either, which results in a memory region that will
1088 not be affected by reboots.
1090 *WARNING* If your board configuration uses automatic
1091 detection of the RAM size, you must make sure that
1092 this memory test is non-destructive. So far, the
1093 following board configurations are known to be
1096 IVMS8, IVML24, SPD8xx,
1097 HERMES, IP860, RPXlite, LWMON,
1103 In the current implementation, the local variables
1104 space and global environment variables space are
1105 separated. Local variables are those you define by
1106 simply typing `name=value'. To access a local
1107 variable later on, you have write `$name' or
1108 `${name}'; to execute the contents of a variable
1109 directly type `$name' at the command prompt.
1111 Global environment variables are those you use
1112 setenv/printenv to work with. To run a command stored
1113 in such a variable, you need to use the run command,
1114 and you must not use the '$' sign to access them.
1116 To store commands and special characters in a
1117 variable, please use double quotation marks
1118 surrounding the whole text of the variable, instead
1119 of the backslashes before semicolons and special
1122 - Default Environment:
1123 CFG_EXTRA_ENV_SETTINGS
1125 Define this to contain any number of null terminated
1126 strings (variable = value pairs) that will be part of
1127 the default environment compiled into the boot image.
1129 For example, place something like this in your
1130 board's config file:
1132 #define CFG_EXTRA_ENV_SETTINGS \
1136 Warning: This method is based on knowledge about the
1137 internal format how the environment is stored by the
1138 U-Boot code. This is NOT an official, exported
1139 interface! Although it is unlikely that this format
1140 will change soon, there is no guarantee either.
1141 You better know what you are doing here.
1143 Note: overly (ab)use of the default environment is
1144 discouraged. Make sure to check other ways to preset
1145 the environment like the "source" command or the
1148 CONFIG_DELAY_ENVIRONMENT
1150 Normally the environment is loaded when the board is
1151 initialised so that it is available to U-Boot. This inhibits
1152 that so that the environment is not available until
1153 explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL
1154 this is instead controlled by the value of
1155 /config/load-environment.
1157 - Automatic software updates via TFTP server
1159 CONFIG_UPDATE_TFTP_CNT_MAX
1160 CONFIG_UPDATE_TFTP_MSEC_MAX
1162 These options enable and control the auto-update feature;
1163 for a more detailed description refer to doc/README.update.
1165 - MTD Support (mtdparts command, UBI support)
1166 CONFIG_MTD_UBI_WL_THRESHOLD
1167 This parameter defines the maximum difference between the highest
1168 erase counter value and the lowest erase counter value of eraseblocks
1169 of UBI devices. When this threshold is exceeded, UBI starts performing
1170 wear leveling by means of moving data from eraseblock with low erase
1171 counter to eraseblocks with high erase counter.
1173 The default value should be OK for SLC NAND flashes, NOR flashes and
1174 other flashes which have eraseblock life-cycle 100000 or more.
1175 However, in case of MLC NAND flashes which typically have eraseblock
1176 life-cycle less than 10000, the threshold should be lessened (e.g.,
1177 to 128 or 256, although it does not have to be power of 2).
1181 CONFIG_MTD_UBI_BEB_LIMIT
1182 This option specifies the maximum bad physical eraseblocks UBI
1183 expects on the MTD device (per 1024 eraseblocks). If the
1184 underlying flash does not admit of bad eraseblocks (e.g. NOR
1185 flash), this value is ignored.
1187 NAND datasheets often specify the minimum and maximum NVM
1188 (Number of Valid Blocks) for the flashes' endurance lifetime.
1189 The maximum expected bad eraseblocks per 1024 eraseblocks
1190 then can be calculated as "1024 * (1 - MinNVB / MaxNVB)",
1191 which gives 20 for most NANDs (MaxNVB is basically the total
1192 count of eraseblocks on the chip).
1194 To put it differently, if this value is 20, UBI will try to
1195 reserve about 1.9% of physical eraseblocks for bad blocks
1196 handling. And that will be 1.9% of eraseblocks on the entire
1197 NAND chip, not just the MTD partition UBI attaches. This means
1198 that if you have, say, a NAND flash chip admits maximum 40 bad
1199 eraseblocks, and it is split on two MTD partitions of the same
1200 size, UBI will reserve 40 eraseblocks when attaching a
1205 CONFIG_MTD_UBI_FASTMAP
1206 Fastmap is a mechanism which allows attaching an UBI device
1207 in nearly constant time. Instead of scanning the whole MTD device it
1208 only has to locate a checkpoint (called fastmap) on the device.
1209 The on-flash fastmap contains all information needed to attach
1210 the device. Using fastmap makes only sense on large devices where
1211 attaching by scanning takes long. UBI will not automatically install
1212 a fastmap on old images, but you can set the UBI parameter
1213 CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note
1214 that fastmap-enabled images are still usable with UBI implementations
1215 without fastmap support. On typical flash devices the whole fastmap
1216 fits into one PEB. UBI will reserve PEBs to hold two fastmaps.
1218 CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT
1219 Set this parameter to enable fastmap automatically on images
1223 CONFIG_MTD_UBI_FM_DEBUG
1224 Enable UBI fastmap debug
1229 Enable building of SPL globally.
1231 CONFIG_SPL_PANIC_ON_RAW_IMAGE
1232 When defined, SPL will panic() if the image it has
1233 loaded does not have a signature.
1234 Defining this is useful when code which loads images
1235 in SPL cannot guarantee that absolutely all read errors
1237 An example is the LPC32XX MLC NAND driver, which will
1238 consider that a completely unreadable NAND block is bad,
1239 and thus should be skipped silently.
1241 CONFIG_SPL_DISPLAY_PRINT
1242 For ARM, enable an optional function to print more information
1243 about the running system.
1245 CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
1246 Set this for NAND SPL on PPC mpc83xx targets, so that
1247 start.S waits for the rest of the SPL to load before
1248 continuing (the hardware starts execution after just
1249 loading the first page rather than the full 4K).
1252 Support for a lightweight UBI (fastmap) scanner and
1255 CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
1256 CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
1257 CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
1258 CFG_SYS_NAND_ECCPOS, CFG_SYS_NAND_ECCSIZE,
1259 CFG_SYS_NAND_ECCBYTES
1260 Defines the size and behavior of the NAND that SPL uses
1263 CFG_SYS_NAND_U_BOOT_DST
1264 Location in memory to load U-Boot to
1266 CFG_SYS_NAND_U_BOOT_SIZE
1267 Size of image to load
1269 CFG_SYS_NAND_U_BOOT_START
1270 Entry point in loaded image to jump to
1272 CONFIG_SPL_RAM_DEVICE
1273 Support for running image already present in ram, in SPL binary
1275 CONFIG_SPL_FIT_PRINT
1276 Printing information about a FIT image adds quite a bit of
1277 code to SPL. So this is normally disabled in SPL. Use this
1278 option to re-enable it. This will affect the output of the
1279 bootm command when booting a FIT image.
1281 - Interrupt support (PPC):
1283 There are common interrupt_init() and timer_interrupt()
1284 for all PPC archs. interrupt_init() calls interrupt_init_cpu()
1285 for CPU specific initialization. interrupt_init_cpu()
1286 should set decrementer_count to appropriate value. If
1287 CPU resets decrementer automatically after interrupt
1288 (ppc4xx) it should set decrementer_count to zero.
1289 timer_interrupt() calls timer_interrupt_cpu() for CPU
1290 specific handling. If board has watchdog / status_led
1291 / other_activity_monitor it works automatically from
1292 general timer_interrupt().
1295 Board initialization settings:
1296 ------------------------------
1298 During Initialization u-boot calls a number of board specific functions
1299 to allow the preparation of board specific prerequisites, e.g. pin setup
1300 before drivers are initialized. To enable these callbacks the
1301 following configuration macros have to be defined. Currently this is
1302 architecture specific, so please check arch/your_architecture/lib/board.c
1303 typically in board_init_f() and board_init_r().
1305 - CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
1306 - CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
1307 - CONFIG_BOARD_LATE_INIT: Call board_late_init()
1309 Configuration Settings:
1310 -----------------------
1312 - MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.
1313 Optionally it can be defined to support 64-bit memory commands.
1315 - CONFIG_SYS_LONGHELP: Defined when you want long help messages included;
1316 undefine this when you're short of memory.
1318 - CFG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default
1319 width of the commands listed in the 'help' command output.
1321 - CONFIG_SYS_PROMPT: This is what U-Boot prints on the console to
1322 prompt for user input.
1324 - CFG_SYS_BAUDRATE_TABLE:
1325 List of legal baudrate settings for this board.
1327 - CFG_SYS_MEM_RESERVE_SECURE
1328 Only implemented for ARMv8 for now.
1329 If defined, the size of CFG_SYS_MEM_RESERVE_SECURE memory
1330 is substracted from total RAM and won't be reported to OS.
1331 This memory can be used as secure memory. A variable
1332 gd->arch.secure_ram is used to track the location. In systems
1333 the RAM base is not zero, or RAM is divided into banks,
1334 this variable needs to be recalcuated to get the address.
1336 - CFG_SYS_SDRAM_BASE:
1337 Physical start address of SDRAM. _Must_ be 0 here.
1339 - CFG_SYS_FLASH_BASE:
1340 Physical start address of Flash memory.
1342 - CONFIG_SYS_MALLOC_LEN:
1343 Size of DRAM reserved for malloc() use.
1345 - CONFIG_SYS_MALLOC_F_LEN
1346 Size of the malloc() pool for use before relocation. If
1347 this is defined, then a very simple malloc() implementation
1348 will become available before relocation. The address is just
1349 below the global data, and the stack is moved down to make
1352 This feature allocates regions with increasing addresses
1353 within the region. calloc() is supported, but realloc()
1354 is not available. free() is supported but does nothing.
1355 The memory will be freed (or in fact just forgotten) when
1356 U-Boot relocates itself.
1358 - CONFIG_SYS_MALLOC_SIMPLE
1359 Provides a simple and small malloc() and calloc() for those
1360 boards which do not use the full malloc in SPL (which is
1361 enabled with CONFIG_SYS_SPL_MALLOC).
1363 - CFG_SYS_BOOTMAPSZ:
1364 Maximum size of memory mapped by the startup code of
1365 the Linux kernel; all data that must be processed by
1366 the Linux kernel (bd_info, boot arguments, FDT blob if
1367 used) must be put below this limit, unless "bootm_low"
1368 environment variable is defined and non-zero. In such case
1369 all data for the Linux kernel must be between "bootm_low"
1370 and "bootm_low" + CFG_SYS_BOOTMAPSZ. The environment
1371 variable "bootm_mapsize" will override the value of
1372 CFG_SYS_BOOTMAPSZ. If CFG_SYS_BOOTMAPSZ is undefined,
1373 then the value in "bootm_size" will be used instead.
1375 - CONFIG_SYS_BOOT_GET_CMDLINE:
1376 Enables allocating and saving kernel cmdline in space between
1377 "bootm_low" and "bootm_low" + BOOTMAPSZ.
1379 - CONFIG_SYS_BOOT_GET_KBD:
1380 Enables allocating and saving a kernel copy of the bd_info in
1381 space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
1383 - CONFIG_SYS_FLASH_PROTECTION
1384 If defined, hardware flash sectors protection is used
1385 instead of U-Boot software protection.
1387 - CONFIG_SYS_FLASH_CFI:
1388 Define if the flash driver uses extra elements in the
1389 common flash structure for storing flash geometry.
1391 - CONFIG_FLASH_CFI_DRIVER
1392 This option also enables the building of the cfi_flash driver
1393 in the drivers directory
1395 - CONFIG_FLASH_CFI_MTD
1396 This option enables the building of the cfi_mtd driver
1397 in the drivers directory. The driver exports CFI flash
1400 - CONFIG_SYS_FLASH_USE_BUFFER_WRITE
1401 Use buffered writes to flash.
1403 - CONFIG_ENV_FLAGS_LIST_DEFAULT
1404 - CFG_ENV_FLAGS_LIST_STATIC
1405 Enable validation of the values given to environment variables when
1406 calling env set. Variables can be restricted to only decimal,
1407 hexadecimal, or boolean. If CONFIG_CMD_NET is also defined,
1408 the variables can also be restricted to IP address or MAC address.
1410 The format of the list is:
1411 type_attribute = [s|d|x|b|i|m]
1412 access_attribute = [a|r|o|c]
1413 attributes = type_attribute[access_attribute]
1414 entry = variable_name[:attributes]
1417 The type attributes are:
1418 s - String (default)
1421 b - Boolean ([1yYtT|0nNfF])
1425 The access attributes are:
1431 - CONFIG_ENV_FLAGS_LIST_DEFAULT
1432 Define this to a list (string) to define the ".flags"
1433 environment variable in the default or embedded environment.
1435 - CFG_ENV_FLAGS_LIST_STATIC
1436 Define this to a list (string) to define validation that
1437 should be done if an entry is not found in the ".flags"
1438 environment variable. To override a setting in the static
1439 list, simply add an entry for the same variable name to the
1442 If CONFIG_REGEX is defined, the variable_name above is evaluated as a
1443 regular expression. This allows multiple variables to define the same
1444 flags without explicitly listing them for each variable.
1446 The following definitions that deal with the placement and management
1447 of environment data (variable area); in general, we support the
1448 following configurations:
1450 BE CAREFUL! The first access to the environment happens quite early
1451 in U-Boot initialization (when we try to get the setting of for the
1452 console baudrate). You *MUST* have mapped your NVRAM area then, or
1455 Please note that even with NVRAM we still use a copy of the
1456 environment in RAM: we could work on NVRAM directly, but we want to
1457 keep settings there always unmodified except somebody uses "saveenv"
1458 to save the current settings.
1460 BE CAREFUL! For some special cases, the local device can not use
1461 "saveenv" command. For example, the local device will get the
1462 environment stored in a remote NOR flash by SRIO or PCIE link,
1463 but it can not erase, write this NOR flash by SRIO or PCIE interface.
1465 - CONFIG_NAND_ENV_DST
1467 Defines address in RAM to which the nand_spl code should copy the
1468 environment. If redundant environment is used, it will be copied to
1469 CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.
1471 Please note that the environment is read-only until the monitor
1472 has been relocated to RAM and a RAM copy of the environment has been
1473 created; also, when using EEPROM you will have to use env_get_f()
1474 until then to read environment variables.
1476 The environment is protected by a CRC32 checksum. Before the monitor
1477 is relocated into RAM, as a result of a bad CRC you will be working
1478 with the compiled-in default environment - *silently*!!! [This is
1479 necessary, because the first environment variable we need is the
1480 "baudrate" setting for the console - if we have a bad CRC, we don't
1481 have any device yet where we could complain.]
1483 Note: once the monitor has been relocated, then it will complain if
1484 the default environment is used; a new CRC is computed as soon as you
1485 use the "saveenv" command to store a valid environment.
1487 - CONFIG_SYS_FAULT_MII_ADDR:
1488 MII address of the PHY to check for the Ethernet link state.
1490 - CONFIG_DISPLAY_BOARDINFO
1491 Display information about the board that U-Boot is running on
1492 when U-Boot starts up. The board function checkboard() is called
1495 - CONFIG_DISPLAY_BOARDINFO_LATE
1496 Similar to the previous option, but display this information
1497 later, once stdio is running and output goes to the LCD, if
1500 Low Level (hardware related) configuration options:
1501 ---------------------------------------------------
1503 - CONFIG_SYS_CACHELINE_SIZE:
1504 Cache Line Size of the CPU.
1506 - CONFIG_SYS_CCSRBAR_DEFAULT:
1507 Default (power-on reset) physical address of CCSR on Freescale
1511 Virtual address of CCSR. On a 32-bit build, this is typically
1512 the same value as CONFIG_SYS_CCSRBAR_DEFAULT.
1514 - CFG_SYS_CCSRBAR_PHYS:
1515 Physical address of CCSR. CCSR can be relocated to a new
1516 physical address, if desired. In this case, this macro should
1517 be set to that address. Otherwise, it should be set to the
1518 same value as CONFIG_SYS_CCSRBAR_DEFAULT. For example, CCSR
1519 is typically relocated on 36-bit builds. It is recommended
1520 that this macro be defined via the _HIGH and _LOW macros:
1522 #define CFG_SYS_CCSRBAR_PHYS ((CFG_SYS_CCSRBAR_PHYS_HIGH
1523 * 1ull) << 32 | CFG_SYS_CCSRBAR_PHYS_LOW)
1525 - CFG_SYS_CCSRBAR_PHYS_HIGH:
1526 Bits 33-36 of CFG_SYS_CCSRBAR_PHYS. This value is typically
1527 either 0 (32-bit build) or 0xF (36-bit build). This macro is
1528 used in assembly code, so it must not contain typecasts or
1529 integer size suffixes (e.g. "ULL").
1531 - CFG_SYS_CCSRBAR_PHYS_LOW:
1532 Lower 32-bits of CFG_SYS_CCSRBAR_PHYS. This macro is
1533 used in assembly code, so it must not contain typecasts or
1534 integer size suffixes (e.g. "ULL").
1536 - CONFIG_SYS_IMMR: Physical address of the Internal Memory.
1537 DO NOT CHANGE unless you know exactly what you're
1538 doing! (11-4) [MPC8xx systems only]
1540 - CFG_SYS_INIT_RAM_ADDR:
1542 Start address of memory area that can be used for
1543 initial data and stack; please note that this must be
1544 writable memory that is working WITHOUT special
1545 initialization, i. e. you CANNOT use normal RAM which
1546 will become available only after programming the
1547 memory controller and running certain initialization
1550 U-Boot uses the following memory types:
1551 - MPC8xx: IMMR (internal memory of the CPU)
1553 - CONFIG_SYS_SCCR: System Clock and reset Control Register (15-27)
1555 - CONFIG_SYS_OR_TIMING_SDRAM:
1558 - CONFIG_SYS_SRIOn_MEM_VIRT:
1559 Virtual Address of SRIO port 'n' memory region
1561 - CONFIG_SYS_SRIOn_MEM_PHYxS:
1562 Physical Address of SRIO port 'n' memory region
1564 - CONFIG_SYS_SRIOn_MEM_SIZE:
1565 Size of SRIO port 'n' memory region
1567 - CONFIG_SYS_NAND_BUSWIDTH_16BIT
1568 Defined to tell the NAND controller that the NAND chip is using
1570 Not all NAND drivers use this symbol.
1571 Example of drivers that use it:
1572 - drivers/mtd/nand/raw/ndfc.c
1573 - drivers/mtd/nand/raw/mxc_nand.c
1575 - CONFIG_SYS_NDFC_EBC0_CFG
1576 Sets the EBC0_CFG register for the NDFC. If not defined
1577 a default value will be used.
1579 - CONFIG_SYS_SPD_BUS_NUM
1580 If SPD EEPROM is on an I2C bus other than the first
1581 one, specify here. Note that the value must resolve
1582 to something your driver can deal with.
1584 - CONFIG_FSL_DDR_INTERACTIVE
1585 Enable interactive DDR debugging. See doc/README.fsl-ddr.
1587 - CONFIG_FSL_DDR_SYNC_REFRESH
1588 Enable sync of refresh for multiple controllers.
1590 - CONFIG_FSL_DDR_BIST
1591 Enable built-in memory test for Freescale DDR controllers.
1594 Enable RMII mode for all FECs.
1595 Note that this is a global option, we can't
1596 have one FEC in standard MII mode and another in RMII mode.
1598 - CONFIG_CRC32_VERIFY
1599 Add a verify option to the crc32 command.
1602 => crc32 -v <address> <count> <crc32>
1604 Where address/count indicate a memory area
1605 and crc32 is the correct crc32 which the
1609 Add the "loopw" memory command. This only takes effect if
1610 the memory commands are activated globally (CONFIG_CMD_MEMORY).
1612 - CONFIG_CMD_MX_CYCLIC
1613 Add the "mdc" and "mwc" memory commands. These are cyclic
1618 This command will print 4 bytes (10,11,12,13) each 500 ms.
1620 => mwc.l 100 12345678 10
1621 This command will write 12345678 to address 100 all 10 ms.
1623 This only takes effect if the memory commands are activated
1624 globally (CONFIG_CMD_MEMORY).
1627 Set when the currently-running compilation is for an artifact
1628 that will end up in the SPL (as opposed to the TPL or U-Boot
1629 proper). Code that needs stage-specific behavior should check
1633 Set when the currently-running compilation is for an artifact
1634 that will end up in the TPL (as opposed to the SPL or U-Boot
1635 proper). Code that needs stage-specific behavior should check
1638 - CONFIG_ARCH_MAP_SYSMEM
1639 Generally U-Boot (and in particular the md command) uses
1640 effective address. It is therefore not necessary to regard
1641 U-Boot address as virtual addresses that need to be translated
1642 to physical addresses. However, sandbox requires this, since
1643 it maintains its own little RAM buffer which contains all
1644 addressable memory. This option causes some memory accesses
1645 to be mapped through map_sysmem() / unmap_sysmem().
1647 - CONFIG_X86_RESET_VECTOR
1648 If defined, the x86 reset vector code is included. This is not
1649 needed when U-Boot is running from Coreboot.
1651 Freescale QE/FMAN Firmware Support:
1652 -----------------------------------
1654 The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the
1655 loading of "firmware", which is encoded in the QE firmware binary format.
1656 This firmware often needs to be loaded during U-Boot booting, so macros
1657 are used to identify the storage device (NOR flash, SPI, etc) and the address
1660 - CONFIG_SYS_FMAN_FW_ADDR
1661 The address in the storage device where the FMAN microcode is located. The
1662 meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
1665 - CONFIG_SYS_QE_FW_ADDR
1666 The address in the storage device where the QE microcode is located. The
1667 meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
1670 - CONFIG_SYS_QE_FMAN_FW_LENGTH
1671 The maximum possible size of the firmware. The firmware binary format
1672 has a field that specifies the actual size of the firmware, but it
1673 might not be possible to read any part of the firmware unless some
1674 local storage is allocated to hold the entire firmware first.
1676 - CONFIG_SYS_QE_FMAN_FW_IN_NOR
1677 Specifies that QE/FMAN firmware is located in NOR flash, mapped as
1678 normal addressable memory via the LBC. CONFIG_SYS_FMAN_FW_ADDR is the
1679 virtual address in NOR flash.
1681 - CONFIG_SYS_QE_FMAN_FW_IN_NAND
1682 Specifies that QE/FMAN firmware is located in NAND flash.
1683 CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.
1685 - CONFIG_SYS_QE_FMAN_FW_IN_MMC
1686 Specifies that QE/FMAN firmware is located on the primary SD/MMC
1687 device. CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.
1689 - CONFIG_SYS_QE_FMAN_FW_IN_REMOTE
1690 Specifies that QE/FMAN firmware is located in the remote (master)
1691 memory space. CONFIG_SYS_FMAN_FW_ADDR is a virtual address which
1692 can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound
1693 window->master inbound window->master LAW->the ucode address in
1694 master's memory space.
1696 Freescale Layerscape Management Complex Firmware Support:
1697 ---------------------------------------------------------
1698 The Freescale Layerscape Management Complex (MC) supports the loading of
1700 This firmware often needs to be loaded during U-Boot booting, so macros
1701 are used to identify the storage device (NOR flash, SPI, etc) and the address
1704 - CONFIG_FSL_MC_ENET
1705 Enable the MC driver for Layerscape SoCs.
1707 Freescale Layerscape Debug Server Support:
1708 -------------------------------------------
1709 The Freescale Layerscape Debug Server Support supports the loading of
1710 "Debug Server firmware" and triggering SP boot-rom.
1711 This firmware often needs to be loaded during U-Boot booting.
1713 - CONFIG_SYS_MC_RSV_MEM_ALIGN
1714 Define alignment of reserved memory MC requires
1719 In order to achieve reproducible builds, timestamps used in the U-Boot build
1720 process have to be set to a fixed value.
1722 This is done using the SOURCE_DATE_EPOCH environment variable.
1723 SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
1724 option for U-Boot or an environment variable in U-Boot.
1726 SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
1728 Building the Software:
1729 ======================
1731 Building U-Boot has been tested in several native build environments
1732 and in many different cross environments. Of course we cannot support
1733 all possibly existing versions of cross development tools in all
1734 (potentially obsolete) versions. In case of tool chain problems we
1735 recommend to use the ELDK (see https://www.denx.de/wiki/DULG/ELDK)
1736 which is extensively used to build and test U-Boot.
1738 If you are not using a native environment, it is assumed that you
1739 have GNU cross compiling tools available in your path. In this case,
1740 you must set the environment variable CROSS_COMPILE in your shell.
1741 Note that no changes to the Makefile or any other source files are
1742 necessary. For example using the ELDK on a 4xx CPU, please enter:
1744 $ CROSS_COMPILE=ppc_4xx-
1745 $ export CROSS_COMPILE
1747 U-Boot is intended to be simple to build. After installing the
1748 sources you must configure U-Boot for one specific board type. This
1753 where "NAME_defconfig" is the name of one of the existing configu-
1754 rations; see configs/*_defconfig for supported names.
1756 Note: for some boards special configuration names may exist; check if
1757 additional information is available from the board vendor; for
1758 instance, the TQM823L systems are available without (standard)
1759 or with LCD support. You can select such additional "features"
1760 when choosing the configuration, i. e.
1762 make TQM823L_defconfig
1763 - will configure for a plain TQM823L, i. e. no LCD support
1765 make TQM823L_LCD_defconfig
1766 - will configure for a TQM823L with U-Boot console on LCD
1771 Finally, type "make all", and you should get some working U-Boot
1772 images ready for download to / installation on your system:
1774 - "u-boot.bin" is a raw binary image
1775 - "u-boot" is an image in ELF binary format
1776 - "u-boot.srec" is in Motorola S-Record format
1778 By default the build is performed locally and the objects are saved
1779 in the source directory. One of the two methods can be used to change
1780 this behavior and build U-Boot to some external directory:
1782 1. Add O= to the make command line invocations:
1784 make O=/tmp/build distclean
1785 make O=/tmp/build NAME_defconfig
1786 make O=/tmp/build all
1788 2. Set environment variable KBUILD_OUTPUT to point to the desired location:
1790 export KBUILD_OUTPUT=/tmp/build
1795 Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
1798 User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by
1799 setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.
1800 For example to treat all compiler warnings as errors:
1802 make KCFLAGS=-Werror
1804 Please be aware that the Makefiles assume you are using GNU make, so
1805 for instance on NetBSD you might need to use "gmake" instead of
1809 If the system board that you have is not listed, then you will need
1810 to port U-Boot to your hardware platform. To do this, follow these
1813 1. Create a new directory to hold your board specific code. Add any
1814 files you need. In your board directory, you will need at least
1815 the "Makefile" and a "<board>.c".
1816 2. Create a new configuration file "include/configs/<board>.h" for
1818 3. If you're porting U-Boot to a new CPU, then also create a new
1819 directory to hold your CPU specific code. Add any files you need.
1820 4. Run "make <board>_defconfig" with your new name.
1821 5. Type "make", and you should get a working "u-boot.srec" file
1822 to be installed on your target system.
1823 6. Debug and solve any problems that might arise.
1824 [Of course, this last step is much harder than it sounds.]
1827 Testing of U-Boot Modifications, Ports to New Hardware, etc.:
1828 ==============================================================
1830 If you have modified U-Boot sources (for instance added a new board
1831 or support for new devices, a new CPU, etc.) you are expected to
1832 provide feedback to the other developers. The feedback normally takes
1833 the form of a "patch", i.e. a context diff against a certain (latest
1834 official or latest in the git repository) version of U-Boot sources.
1836 But before you submit such a patch, please verify that your modifi-
1837 cation did not break existing code. At least make sure that *ALL* of
1838 the supported boards compile WITHOUT ANY compiler warnings. To do so,
1839 just run the buildman script (tools/buildman/buildman), which will
1840 configure and build U-Boot for ALL supported system. Be warned, this
1841 will take a while. Please see the buildman README, or run 'buildman -H'
1845 See also "U-Boot Porting Guide" below.
1848 Monitor Commands - Overview:
1849 ============================
1851 go - start application at address 'addr'
1852 run - run commands in an environment variable
1853 bootm - boot application image from memory
1854 bootp - boot image via network using BootP/TFTP protocol
1855 bootz - boot zImage from memory
1856 tftpboot- boot image via network using TFTP protocol
1857 and env variables "ipaddr" and "serverip"
1858 (and eventually "gatewayip")
1859 tftpput - upload a file via network using TFTP protocol
1860 rarpboot- boot image via network using RARP/TFTP protocol
1861 diskboot- boot from IDE devicebootd - boot default, i.e., run 'bootcmd'
1862 loads - load S-Record file over serial line
1863 loadb - load binary file over serial line (kermit mode)
1864 loadm - load binary blob from source address to destination address
1866 mm - memory modify (auto-incrementing)
1867 nm - memory modify (constant address)
1868 mw - memory write (fill)
1871 cmp - memory compare
1872 crc32 - checksum calculation
1873 i2c - I2C sub-system
1874 sspi - SPI utility commands
1875 base - print or set address offset
1876 printenv- print environment variables
1877 pwm - control pwm channels
1878 setenv - set environment variables
1879 saveenv - save environment variables to persistent storage
1880 protect - enable or disable FLASH write protection
1881 erase - erase FLASH memory
1882 flinfo - print FLASH memory information
1883 nand - NAND memory operations (see doc/README.nand)
1884 bdinfo - print Board Info structure
1885 iminfo - print header information for application image
1886 coninfo - print console devices and informations
1887 ide - IDE sub-system
1888 loop - infinite loop on address range
1889 loopw - infinite write loop on address range
1890 mtest - simple RAM test
1891 icache - enable or disable instruction cache
1892 dcache - enable or disable data cache
1893 reset - Perform RESET of the CPU
1894 echo - echo args to console
1895 version - print monitor version
1896 help - print online help
1897 ? - alias for 'help'
1900 Monitor Commands - Detailed Description:
1901 ========================================
1905 For now: just type "help <command>".
1908 Note for Redundant Ethernet Interfaces:
1909 =======================================
1911 Some boards come with redundant Ethernet interfaces; U-Boot supports
1912 such configurations and is capable of automatic selection of a
1913 "working" interface when needed. MAC assignment works as follows:
1915 Network interfaces are numbered eth0, eth1, eth2, ... Corresponding
1916 MAC addresses can be stored in the environment as "ethaddr" (=>eth0),
1917 "eth1addr" (=>eth1), "eth2addr", ...
1919 If the network interface stores some valid MAC address (for instance
1920 in SROM), this is used as default address if there is NO correspon-
1921 ding setting in the environment; if the corresponding environment
1922 variable is set, this overrides the settings in the card; that means:
1924 o If the SROM has a valid MAC address, and there is no address in the
1925 environment, the SROM's address is used.
1927 o If there is no valid address in the SROM, and a definition in the
1928 environment exists, then the value from the environment variable is
1931 o If both the SROM and the environment contain a MAC address, and
1932 both addresses are the same, this MAC address is used.
1934 o If both the SROM and the environment contain a MAC address, and the
1935 addresses differ, the value from the environment is used and a
1938 o If neither SROM nor the environment contain a MAC address, an error
1939 is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
1940 a random, locally-assigned MAC is used.
1942 If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresses
1943 will be programmed into hardware as part of the initialization process. This
1944 may be skipped by setting the appropriate 'ethmacskip' environment variable.
1945 The naming convention is as follows:
1946 "ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.
1951 U-Boot is capable of booting (and performing other auxiliary operations on)
1952 images in two formats:
1954 New uImage format (FIT)
1955 -----------------------
1957 Flexible and powerful format based on Flattened Image Tree -- FIT (similar
1958 to Flattened Device Tree). It allows the use of images with multiple
1959 components (several kernels, ramdisks, etc.), with contents protected by
1960 SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.
1966 Old image format is based on binary files which can be basically anything,
1967 preceded by a special header; see the definitions in include/image.h for
1968 details; basically, the header defines the following image properties:
1970 * Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
1971 4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
1972 LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
1973 Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, INTEGRITY).
1974 * Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
1975 IA64, MIPS, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
1976 Currently supported: ARM, Intel x86, MIPS, Nios II, PowerPC).
1977 * Compression Type (uncompressed, gzip, bzip2)
1983 The header is marked by a special Magic Number, and both the header
1984 and the data portions of the image are secured against corruption by
1991 Although U-Boot should support any OS or standalone application
1992 easily, the main focus has always been on Linux during the design of
1995 U-Boot includes many features that so far have been part of some
1996 special "boot loader" code within the Linux kernel. Also, any
1997 "initrd" images to be used are no longer part of one big Linux image;
1998 instead, kernel and "initrd" are separate images. This implementation
1999 serves several purposes:
2001 - the same features can be used for other OS or standalone
2002 applications (for instance: using compressed images to reduce the
2003 Flash memory footprint)
2005 - it becomes much easier to port new Linux kernel versions because
2006 lots of low-level, hardware dependent stuff are done by U-Boot
2008 - the same Linux kernel image can now be used with different "initrd"
2009 images; of course this also means that different kernel images can
2010 be run with the same "initrd". This makes testing easier (you don't
2011 have to build a new "zImage.initrd" Linux image when you just
2012 change a file in your "initrd"). Also, a field-upgrade of the
2013 software is easier now.
2019 Porting Linux to U-Boot based systems:
2020 ---------------------------------------
2022 U-Boot cannot save you from doing all the necessary modifications to
2023 configure the Linux device drivers for use with your target hardware
2024 (no, we don't intend to provide a full virtual machine interface to
2027 But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).
2029 Just make sure your machine specific header file (for instance
2030 include/asm-ppc/tqm8xx.h) includes the same definition of the Board
2031 Information structure as we define in include/asm-<arch>/u-boot.h,
2032 and make sure that your definition of IMAP_ADDR uses the same value
2033 as your U-Boot configuration in CONFIG_SYS_IMMR.
2035 Note that U-Boot now has a driver model, a unified model for drivers.
2036 If you are adding a new driver, plumb it into driver model. If there
2037 is no uclass available, you are encouraged to create one. See
2041 Configuring the Linux kernel:
2042 -----------------------------
2044 No specific requirements for U-Boot. Make sure you have some root
2045 device (initial ramdisk, NFS) for your target system.
2048 Building a Linux Image:
2049 -----------------------
2051 With U-Boot, "normal" build targets like "zImage" or "bzImage" are
2052 not used. If you use recent kernel source, a new build target
2053 "uImage" will exist which automatically builds an image usable by
2054 U-Boot. Most older kernels also have support for a "pImage" target,
2055 which was introduced for our predecessor project PPCBoot and uses a
2056 100% compatible format.
2060 make TQM850L_defconfig
2065 The "uImage" build target uses a special tool (in 'tools/mkimage') to
2066 encapsulate a compressed Linux kernel image with header information,
2067 CRC32 checksum etc. for use with U-Boot. This is what we are doing:
2069 * build a standard "vmlinux" kernel image (in ELF binary format):
2071 * convert the kernel into a raw binary image:
2073 ${CROSS_COMPILE}-objcopy -O binary \
2074 -R .note -R .comment \
2075 -S vmlinux linux.bin
2077 * compress the binary image:
2081 * package compressed binary image for U-Boot:
2083 mkimage -A ppc -O linux -T kernel -C gzip \
2084 -a 0 -e 0 -n "Linux Kernel Image" \
2085 -d linux.bin.gz uImage
2088 The "mkimage" tool can also be used to create ramdisk images for use
2089 with U-Boot, either separated from the Linux kernel image, or
2090 combined into one file. "mkimage" encapsulates the images with a 64
2091 byte header containing information about target architecture,
2092 operating system, image type, compression method, entry points, time
2093 stamp, CRC32 checksums, etc.
2095 "mkimage" can be called in two ways: to verify existing images and
2096 print the header information, or to build new images.
2098 In the first form (with "-l" option) mkimage lists the information
2099 contained in the header of an existing U-Boot image; this includes
2100 checksum verification:
2102 tools/mkimage -l image
2103 -l ==> list image header information
2105 The second form (with "-d" option) is used to build a U-Boot image
2106 from a "data file" which is used as image payload:
2108 tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
2109 -n name -d data_file image
2110 -A ==> set architecture to 'arch'
2111 -O ==> set operating system to 'os'
2112 -T ==> set image type to 'type'
2113 -C ==> set compression type 'comp'
2114 -a ==> set load address to 'addr' (hex)
2115 -e ==> set entry point to 'ep' (hex)
2116 -n ==> set image name to 'name'
2117 -d ==> use image data from 'datafile'
2119 Right now, all Linux kernels for PowerPC systems use the same load
2120 address (0x00000000), but the entry point address depends on the
2123 - 2.2.x kernels have the entry point at 0x0000000C,
2124 - 2.3.x and later kernels have the entry point at 0x00000000.
2126 So a typical call to build a U-Boot image would read:
2128 -> tools/mkimage -n '2.4.4 kernel for TQM850L' \
2129 > -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
2130 > -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
2131 > examples/uImage.TQM850L
2132 Image Name: 2.4.4 kernel for TQM850L
2133 Created: Wed Jul 19 02:34:59 2000
2134 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2135 Data Size: 335725 Bytes = 327.86 kB = 0.32 MB
2136 Load Address: 0x00000000
2137 Entry Point: 0x00000000
2139 To verify the contents of the image (or check for corruption):
2141 -> tools/mkimage -l examples/uImage.TQM850L
2142 Image Name: 2.4.4 kernel for TQM850L
2143 Created: Wed Jul 19 02:34:59 2000
2144 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2145 Data Size: 335725 Bytes = 327.86 kB = 0.32 MB
2146 Load Address: 0x00000000
2147 Entry Point: 0x00000000
2149 NOTE: for embedded systems where boot time is critical you can trade
2150 speed for memory and install an UNCOMPRESSED image instead: this
2151 needs more space in Flash, but boots much faster since it does not
2152 need to be uncompressed:
2154 -> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
2155 -> tools/mkimage -n '2.4.4 kernel for TQM850L' \
2156 > -A ppc -O linux -T kernel -C none -a 0 -e 0 \
2157 > -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
2158 > examples/uImage.TQM850L-uncompressed
2159 Image Name: 2.4.4 kernel for TQM850L
2160 Created: Wed Jul 19 02:34:59 2000
2161 Image Type: PowerPC Linux Kernel Image (uncompressed)
2162 Data Size: 792160 Bytes = 773.59 kB = 0.76 MB
2163 Load Address: 0x00000000
2164 Entry Point: 0x00000000
2167 Similar you can build U-Boot images from a 'ramdisk.image.gz' file
2168 when your kernel is intended to use an initial ramdisk:
2170 -> tools/mkimage -n 'Simple Ramdisk Image' \
2171 > -A ppc -O linux -T ramdisk -C gzip \
2172 > -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
2173 Image Name: Simple Ramdisk Image
2174 Created: Wed Jan 12 14:01:50 2000
2175 Image Type: PowerPC Linux RAMDisk Image (gzip compressed)
2176 Data Size: 566530 Bytes = 553.25 kB = 0.54 MB
2177 Load Address: 0x00000000
2178 Entry Point: 0x00000000
2180 The "dumpimage" tool can be used to disassemble or list the contents of images
2181 built by mkimage. See dumpimage's help output (-h) for details.
2183 Installing a Linux Image:
2184 -------------------------
2186 To downloading a U-Boot image over the serial (console) interface,
2187 you must convert the image to S-Record format:
2189 objcopy -I binary -O srec examples/image examples/image.srec
2191 The 'objcopy' does not understand the information in the U-Boot
2192 image header, so the resulting S-Record file will be relative to
2193 address 0x00000000. To load it to a given address, you need to
2194 specify the target address as 'offset' parameter with the 'loads'
2197 Example: install the image to address 0x40100000 (which on the
2198 TQM8xxL is in the first Flash bank):
2200 => erase 40100000 401FFFFF
2206 ## Ready for S-Record download ...
2207 ~>examples/image.srec
2208 1 2 3 4 5 6 7 8 9 10 11 12 13 ...
2210 15989 15990 15991 15992
2211 [file transfer complete]
2213 ## Start Addr = 0x00000000
2216 You can check the success of the download using the 'iminfo' command;
2217 this includes a checksum verification so you can be sure no data
2218 corruption happened:
2222 ## Checking Image at 40100000 ...
2223 Image Name: 2.2.13 for initrd on TQM850L
2224 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2225 Data Size: 335725 Bytes = 327 kB = 0 MB
2226 Load Address: 00000000
2227 Entry Point: 0000000c
2228 Verifying Checksum ... OK
2234 The "bootm" command is used to boot an application that is stored in
2235 memory (RAM or Flash). In case of a Linux kernel image, the contents
2236 of the "bootargs" environment variable is passed to the kernel as
2237 parameters. You can check and modify this variable using the
2238 "printenv" and "setenv" commands:
2241 => printenv bootargs
2242 bootargs=root=/dev/ram
2244 => setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
2246 => printenv bootargs
2247 bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
2250 ## Booting Linux kernel at 40020000 ...
2251 Image Name: 2.2.13 for NFS on TQM850L
2252 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2253 Data Size: 381681 Bytes = 372 kB = 0 MB
2254 Load Address: 00000000
2255 Entry Point: 0000000c
2256 Verifying Checksum ... OK
2257 Uncompressing Kernel Image ... OK
2258 Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000
2259 Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
2260 time_init: decrementer frequency = 187500000/60
2261 Calibrating delay loop... 49.77 BogoMIPS
2262 Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
2265 If you want to boot a Linux kernel with initial RAM disk, you pass
2266 the memory addresses of both the kernel and the initrd image (PPBCOOT
2267 format!) to the "bootm" command:
2269 => imi 40100000 40200000
2271 ## Checking Image at 40100000 ...
2272 Image Name: 2.2.13 for initrd on TQM850L
2273 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2274 Data Size: 335725 Bytes = 327 kB = 0 MB
2275 Load Address: 00000000
2276 Entry Point: 0000000c
2277 Verifying Checksum ... OK
2279 ## Checking Image at 40200000 ...
2280 Image Name: Simple Ramdisk Image
2281 Image Type: PowerPC Linux RAMDisk Image (gzip compressed)
2282 Data Size: 566530 Bytes = 553 kB = 0 MB
2283 Load Address: 00000000
2284 Entry Point: 00000000
2285 Verifying Checksum ... OK
2287 => bootm 40100000 40200000
2288 ## Booting Linux kernel at 40100000 ...
2289 Image Name: 2.2.13 for initrd on TQM850L
2290 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2291 Data Size: 335725 Bytes = 327 kB = 0 MB
2292 Load Address: 00000000
2293 Entry Point: 0000000c
2294 Verifying Checksum ... OK
2295 Uncompressing Kernel Image ... OK
2296 ## Loading RAMDisk Image at 40200000 ...
2297 Image Name: Simple Ramdisk Image
2298 Image Type: PowerPC Linux RAMDisk Image (gzip compressed)
2299 Data Size: 566530 Bytes = 553 kB = 0 MB
2300 Load Address: 00000000
2301 Entry Point: 00000000
2302 Verifying Checksum ... OK
2303 Loading Ramdisk ... OK
2304 Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000
2305 Boot arguments: root=/dev/ram
2306 time_init: decrementer frequency = 187500000/60
2307 Calibrating delay loop... 49.77 BogoMIPS
2309 RAMDISK: Compressed image found at block 0
2310 VFS: Mounted root (ext2 filesystem).
2314 Boot Linux and pass a flat device tree:
2317 First, U-Boot must be compiled with the appropriate defines. See the section
2318 titled "Linux Kernel Interface" above for a more in depth explanation. The
2319 following is an example of how to start a kernel and pass an updated
2325 oft=oftrees/mpc8540ads.dtb
2326 => tftp $oftaddr $oft
2327 Speed: 1000, full duplex
2329 TFTP from server 192.168.1.1; our IP address is 192.168.1.101
2330 Filename 'oftrees/mpc8540ads.dtb'.
2331 Load address: 0x300000
2334 Bytes transferred = 4106 (100a hex)
2335 => tftp $loadaddr $bootfile
2336 Speed: 1000, full duplex
2338 TFTP from server 192.168.1.1; our IP address is 192.168.1.2
2340 Load address: 0x200000
2341 Loading:############
2343 Bytes transferred = 1029407 (fb51f hex)
2348 => bootm $loadaddr - $oftaddr
2349 ## Booting image at 00200000 ...
2350 Image Name: Linux-2.6.17-dirty
2351 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2352 Data Size: 1029343 Bytes = 1005.2 kB
2353 Load Address: 00000000
2354 Entry Point: 00000000
2355 Verifying Checksum ... OK
2356 Uncompressing Kernel Image ... OK
2357 Booting using flat device tree at 0x300000
2358 Using MPC85xx ADS machine description
2359 Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
2363 More About U-Boot Image Types:
2364 ------------------------------
2366 U-Boot supports the following image types:
2368 "Standalone Programs" are directly runnable in the environment
2369 provided by U-Boot; it is expected that (if they behave
2370 well) you can continue to work in U-Boot after return from
2371 the Standalone Program.
2372 "OS Kernel Images" are usually images of some Embedded OS which
2373 will take over control completely. Usually these programs
2374 will install their own set of exception handlers, device
2375 drivers, set up the MMU, etc. - this means, that you cannot
2376 expect to re-enter U-Boot except by resetting the CPU.
2377 "RAMDisk Images" are more or less just data blocks, and their
2378 parameters (address, size) are passed to an OS kernel that is
2380 "Multi-File Images" contain several images, typically an OS
2381 (Linux) kernel image and one or more data images like
2382 RAMDisks. This construct is useful for instance when you want
2383 to boot over the network using BOOTP etc., where the boot
2384 server provides just a single image file, but you want to get
2385 for instance an OS kernel and a RAMDisk image.
2387 "Multi-File Images" start with a list of image sizes, each
2388 image size (in bytes) specified by an "uint32_t" in network
2389 byte order. This list is terminated by an "(uint32_t)0".
2390 Immediately after the terminating 0 follow the images, one by
2391 one, all aligned on "uint32_t" boundaries (size rounded up to
2392 a multiple of 4 bytes).
2394 "Firmware Images" are binary images containing firmware (like
2395 U-Boot or FPGA images) which usually will be programmed to
2398 "Script files" are command sequences that will be executed by
2399 U-Boot's command interpreter; this feature is especially
2400 useful when you configure U-Boot to use a real shell (hush)
2401 as command interpreter.
2403 Booting the Linux zImage:
2404 -------------------------
2406 On some platforms, it's possible to boot Linux zImage. This is done
2407 using the "bootz" command. The syntax of "bootz" command is the same
2408 as the syntax of "bootm" command.
2410 Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply
2411 kernel with raw initrd images. The syntax is slightly different, the
2412 address of the initrd must be augmented by it's size, in the following
2413 format: "<initrd addres>:<initrd size>".
2419 One of the features of U-Boot is that you can dynamically load and
2420 run "standalone" applications, which can use some resources of
2421 U-Boot like console I/O functions or interrupt services.
2423 Two simple examples are included with the sources:
2428 'examples/hello_world.c' contains a small "Hello World" Demo
2429 application; it is automatically compiled when you build U-Boot.
2430 It's configured to run at address 0x00040004, so you can play with it
2434 ## Ready for S-Record download ...
2435 ~>examples/hello_world.srec
2436 1 2 3 4 5 6 7 8 9 10 11 ...
2437 [file transfer complete]
2439 ## Start Addr = 0x00040004
2441 => go 40004 Hello World! This is a test.
2442 ## Starting application at 0x00040004 ...
2453 Hit any key to exit ...
2455 ## Application terminated, rc = 0x0
2457 Another example, which demonstrates how to register a CPM interrupt
2458 handler with the U-Boot code, can be found in 'examples/timer.c'.
2459 Here, a CPM timer is set up to generate an interrupt every second.
2460 The interrupt service routine is trivial, just printing a '.'
2461 character, but this is just a demo program. The application can be
2462 controlled by the following keys:
2464 ? - print current values og the CPM Timer registers
2465 b - enable interrupts and start timer
2466 e - stop timer and disable interrupts
2467 q - quit application
2470 ## Ready for S-Record download ...
2471 ~>examples/timer.srec
2472 1 2 3 4 5 6 7 8 9 10 11 ...
2473 [file transfer complete]
2475 ## Start Addr = 0x00040004
2478 ## Starting application at 0x00040004 ...
2481 tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
2484 [q, b, e, ?] Set interval 1000000 us
2487 [q, b, e, ?] ........
2488 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
2491 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
2494 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
2497 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
2499 [q, b, e, ?] ...Stopping timer
2501 [q, b, e, ?] ## Application terminated, rc = 0x0
2507 Over time, many people have reported problems when trying to use the
2508 "minicom" terminal emulation program for serial download. I (wd)
2509 consider minicom to be broken, and recommend not to use it. Under
2510 Unix, I recommend to use C-Kermit for general purpose use (and
2511 especially for kermit binary protocol download ("loadb" command), and
2512 use "cu" for S-Record download ("loads" command). See
2513 https://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.
2514 for help with kermit.
2517 Nevertheless, if you absolutely want to use it try adding this
2518 configuration to your "File transfer protocols" section:
2520 Name Program Name U/D FullScr IO-Red. Multi
2521 X kermit /usr/bin/kermit -i -l %l -s Y U Y N N
2522 Y kermit /usr/bin/kermit -i -l %l -r N D Y N N
2525 Implementation Internals:
2526 =========================
2528 The following is not intended to be a complete description of every
2529 implementation detail. However, it should help to understand the
2530 inner workings of U-Boot and make it easier to port it to custom
2534 Initial Stack, Global Data:
2535 ---------------------------
2537 The implementation of U-Boot is complicated by the fact that U-Boot
2538 starts running out of ROM (flash memory), usually without access to
2539 system RAM (because the memory controller is not initialized yet).
2540 This means that we don't have writable Data or BSS segments, and BSS
2541 is not initialized as zero. To be able to get a C environment working
2542 at all, we have to allocate at least a minimal stack. Implementation
2543 options for this are defined and restricted by the CPU used: Some CPU
2544 models provide on-chip memory (like the IMMR area on MPC8xx and
2545 MPC826x processors), on others (parts of) the data cache can be
2546 locked as (mis-) used as memory, etc.
2548 Chris Hallinan posted a good summary of these issues to the
2549 U-Boot mailing list:
2551 Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
2552 From: "Chris Hallinan" <clh@net1plus.com>
2553 Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
2556 Correct me if I'm wrong, folks, but the way I understand it
2557 is this: Using DCACHE as initial RAM for Stack, etc, does not
2558 require any physical RAM backing up the cache. The cleverness
2559 is that the cache is being used as a temporary supply of
2560 necessary storage before the SDRAM controller is setup. It's
2561 beyond the scope of this list to explain the details, but you
2562 can see how this works by studying the cache architecture and
2563 operation in the architecture and processor-specific manuals.
2565 OCM is On Chip Memory, which I believe the 405GP has 4K. It
2566 is another option for the system designer to use as an
2567 initial stack/RAM area prior to SDRAM being available. Either
2568 option should work for you. Using CS 4 should be fine if your
2569 board designers haven't used it for something that would
2570 cause you grief during the initial boot! It is frequently not
2573 CFG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
2574 with your processor/board/system design. The default value
2575 you will find in any recent u-boot distribution in
2576 walnut.h should work for you. I'd set it to a value larger
2577 than your SDRAM module. If you have a 64MB SDRAM module, set
2578 it above 400_0000. Just make sure your board has no resources
2579 that are supposed to respond to that address! That code in
2580 start.S has been around a while and should work as is when
2581 you get the config right.
2586 It is essential to remember this, since it has some impact on the C
2587 code for the initialization procedures:
2589 * Initialized global data (data segment) is read-only. Do not attempt
2592 * Do not use any uninitialized global data (or implicitly initialized
2593 as zero data - BSS segment) at all - this is undefined, initiali-
2594 zation is performed later (when relocating to RAM).
2596 * Stack space is very limited. Avoid big data buffers or things like
2599 Having only the stack as writable memory limits means we cannot use
2600 normal global data to share information between the code. But it
2601 turned out that the implementation of U-Boot can be greatly
2602 simplified by making a global data structure (gd_t) available to all
2603 functions. We could pass a pointer to this data as argument to _all_
2604 functions, but this would bloat the code. Instead we use a feature of
2605 the GCC compiler (Global Register Variables) to share the data: we
2606 place a pointer (gd) to the global data into a register which we
2607 reserve for this purpose.
2609 When choosing a register for such a purpose we are restricted by the
2610 relevant (E)ABI specifications for the current architecture, and by
2611 GCC's implementation.
2613 For PowerPC, the following registers have specific use:
2615 R2: reserved for system use
2616 R3-R4: parameter passing and return values
2617 R5-R10: parameter passing
2618 R13: small data area pointer
2622 (U-Boot also uses R12 as internal GOT pointer. r12
2623 is a volatile register so r12 needs to be reset when
2624 going back and forth between asm and C)
2626 ==> U-Boot will use R2 to hold a pointer to the global data
2628 Note: on PPC, we could use a static initializer (since the
2629 address of the global data structure is known at compile time),
2630 but it turned out that reserving a register results in somewhat
2631 smaller code - although the code savings are not that big (on
2632 average for all boards 752 bytes for the whole U-Boot image,
2633 624 text + 127 data).
2635 On ARM, the following registers are used:
2637 R0: function argument word/integer result
2638 R1-R3: function argument word
2639 R9: platform specific
2640 R10: stack limit (used only if stack checking is enabled)
2641 R11: argument (frame) pointer
2642 R12: temporary workspace
2645 R15: program counter
2647 ==> U-Boot will use R9 to hold a pointer to the global data
2649 Note: on ARM, only R_ARM_RELATIVE relocations are supported.
2651 On Nios II, the ABI is documented here:
2652 https://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
2654 ==> U-Boot will use gp to hold a pointer to the global data
2656 Note: on Nios II, we give "-G0" option to gcc and don't use gp
2657 to access small data sections, so gp is free.
2659 On RISC-V, the following registers are used:
2661 x0: hard-wired zero (zero)
2662 x1: return address (ra)
2663 x2: stack pointer (sp)
2664 x3: global pointer (gp)
2665 x4: thread pointer (tp)
2666 x5: link register (t0)
2667 x8: frame pointer (fp)
2668 x10-x11: arguments/return values (a0-1)
2669 x12-x17: arguments (a2-7)
2670 x28-31: temporaries (t3-6)
2671 pc: program counter (pc)
2673 ==> U-Boot will use gp to hold a pointer to the global data
2678 U-Boot runs in system state and uses physical addresses, i.e. the
2679 MMU is not used either for address mapping nor for memory protection.
2681 The available memory is mapped to fixed addresses using the memory
2682 controller. In this process, a contiguous block is formed for each
2683 memory type (Flash, SDRAM, SRAM), even when it consists of several
2684 physical memory banks.
2686 U-Boot is installed in the first 128 kB of the first Flash bank (on
2687 TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
2688 booting and sizing and initializing DRAM, the code relocates itself
2689 to the upper end of DRAM. Immediately below the U-Boot code some
2690 memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
2691 configuration setting]. Below that, a structure with global Board
2692 Info data is placed, followed by the stack (growing downward).
2694 Additionally, some exception handler code is copied to the low 8 kB
2695 of DRAM (0x00000000 ... 0x00001FFF).
2697 So a typical memory configuration with 16 MB of DRAM could look like
2700 0x0000 0000 Exception Vector code
2703 0x0000 2000 Free for Application Use
2709 0x00FB FF20 Monitor Stack (Growing downward)
2710 0x00FB FFAC Board Info Data and permanent copy of global data
2711 0x00FC 0000 Malloc Arena
2714 0x00FE 0000 RAM Copy of Monitor Code
2715 ... eventually: LCD or video framebuffer
2716 ... eventually: pRAM (Protected RAM - unchanged by reset)
2717 0x00FF FFFF [End of RAM]
2720 System Initialization:
2721 ----------------------
2723 In the reset configuration, U-Boot starts at the reset entry point
2724 (on most PowerPC systems at address 0x00000100). Because of the reset
2725 configuration for CS0# this is a mirror of the on board Flash memory.
2726 To be able to re-map memory U-Boot then jumps to its link address.
2727 To be able to implement the initialization code in C, a (small!)
2728 initial stack is set up in the internal Dual Ported RAM (in case CPUs
2729 which provide such a feature like), or in a locked part of the data
2730 cache. After that, U-Boot initializes the CPU core, the caches and
2733 Next, all (potentially) available memory banks are mapped using a
2734 preliminary mapping. For example, we put them on 512 MB boundaries
2735 (multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
2736 on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
2737 programmed for SDRAM access. Using the temporary configuration, a
2738 simple memory test is run that determines the size of the SDRAM
2741 When there is more than one SDRAM bank, and the banks are of
2742 different size, the largest is mapped first. For equal size, the first
2743 bank (CS2#) is mapped first. The first mapping is always for address
2744 0x00000000, with any additional banks following immediately to create
2745 contiguous memory starting from 0.
2747 Then, the monitor installs itself at the upper end of the SDRAM area
2748 and allocates memory for use by malloc() and for the global Board
2749 Info data; also, the exception vector code is copied to the low RAM
2750 pages, and the final stack is set up.
2752 Only after this relocation will you have a "normal" C environment;
2753 until that you are restricted in several ways, mostly because you are
2754 running from ROM, and because the code will have to be relocated to a
2758 U-Boot Porting Guide:
2759 ----------------------
2761 [Based on messages by Jerry Van Baren in the U-Boot-Users mailing
2765 int main(int argc, char *argv[])
2767 sighandler_t no_more_time;
2769 signal(SIGALRM, no_more_time);
2770 alarm(PROJECT_DEADLINE - toSec (3 * WEEK));
2772 if (available_money > available_manpower) {
2773 Pay consultant to port U-Boot;
2777 Download latest U-Boot source;
2779 Subscribe to u-boot mailing list;
2782 email("Hi, I am new to U-Boot, how do I get started?");
2785 Read the README file in the top level directory;
2786 Read https://www.denx.de/wiki/bin/view/DULG/Manual;
2787 Read applicable doc/README.*;
2788 Read the source, Luke;
2789 /* find . -name "*.[chS]" | xargs grep -i <keyword> */
2792 if (available_money > toLocalCurrency ($2500))
2795 Add a lot of aggravation and time;
2797 if (a similar board exists) { /* hopefully... */
2798 cp -a board/<similar> board/<myboard>
2799 cp include/configs/<similar>.h include/configs/<myboard>.h
2801 Create your own board support subdirectory;
2802 Create your own board include/configs/<myboard>.h file;
2804 Edit new board/<myboard> files
2805 Edit new include/configs/<myboard>.h
2810 Add / modify source code;
2814 email("Hi, I am having problems...");
2816 Send patch file to the U-Boot email list;
2817 if (reasonable critiques)
2818 Incorporate improvements from email list code review;
2820 Defend code as written;
2826 void no_more_time (int sig)
2835 The U-Boot projects depends on contributions from the user community.
2836 If you want to participate, please, have a look at the 'General'
2837 section of https://u-boot.readthedocs.io/en/latest/develop/index.html
2838 where we describe coding standards and the patch submission process.