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 /arch Architecture-specific files
112 /arc Files generic to ARC architecture
113 /arm Files generic to ARM architecture
114 /m68k Files generic to m68k architecture
115 /microblaze Files generic to microblaze architecture
116 /mips Files generic to MIPS architecture
117 /nios2 Files generic to Altera NIOS2 architecture
118 /powerpc Files generic to PowerPC architecture
119 /riscv Files generic to RISC-V architecture
120 /sandbox Files generic to HW-independent "sandbox"
121 /sh Files generic to SH architecture
122 /x86 Files generic to x86 architecture
123 /xtensa Files generic to Xtensa architecture
124 /api Machine/arch-independent API for external apps
125 /board Board-dependent files
126 /boot Support for images and booting
127 /cmd U-Boot commands functions
128 /common Misc architecture-independent functions
129 /configs Board default configuration files
130 /disk Code for disk drive partition handling
131 /doc Documentation (a mix of ReST and READMEs)
132 /drivers Device drivers
133 /dts Makefile for building internal U-Boot fdt.
134 /env Environment support
135 /examples Example code for standalone applications, etc.
136 /fs Filesystem code (cramfs, ext2, jffs2, etc.)
137 /include Header Files
138 /lib Library routines generic to all architectures
139 /Licenses Various license files
141 /post Power On Self Test
142 /scripts Various build scripts and Makefiles
143 /test Various unit test files
144 /tools Tools to build and sign FIT images, etc.
146 Software Configuration:
147 =======================
149 Selection of Processor Architecture and Board Type:
150 ---------------------------------------------------
152 For all supported boards there are ready-to-use default
153 configurations available; just type "make <board_name>_defconfig".
155 Example: For a TQM823L module type:
158 make TQM823L_defconfig
160 Note: If you're looking for the default configuration file for a board
161 you're sure used to be there but is now missing, check the file
162 doc/README.scrapyard for a list of no longer supported boards.
167 U-Boot can be built natively to run on a Linux host using the 'sandbox'
168 board. This allows feature development which is not board- or architecture-
169 specific to be undertaken on a native platform. The sandbox is also used to
170 run some of U-Boot's tests.
172 See doc/arch/sandbox/sandbox.rst for more details.
175 Board Initialisation Flow:
176 --------------------------
178 This is the intended start-up flow for boards. This should apply for both
179 SPL and U-Boot proper (i.e. they both follow the same rules).
181 Note: "SPL" stands for "Secondary Program Loader," which is explained in
182 more detail later in this file.
184 At present, SPL mostly uses a separate code path, but the function names
185 and roles of each function are the same. Some boards or architectures
186 may not conform to this. At least most ARM boards which use
187 CONFIG_SPL_FRAMEWORK conform to this.
189 Execution typically starts with an architecture-specific (and possibly
190 CPU-specific) start.S file, such as:
192 - arch/arm/cpu/armv7/start.S
193 - arch/powerpc/cpu/mpc83xx/start.S
194 - arch/mips/cpu/start.S
196 and so on. From there, three functions are called; the purpose and
197 limitations of each of these functions are described below.
200 - purpose: essential init to permit execution to reach board_init_f()
201 - no global_data or BSS
202 - there is no stack (ARMv7 may have one but it will soon be removed)
203 - must not set up SDRAM or use console
204 - must only do the bare minimum to allow execution to continue to
206 - this is almost never needed
207 - return normally from this function
210 - purpose: set up the machine ready for running board_init_r():
211 i.e. SDRAM and serial UART
212 - global_data is available
214 - BSS is not available, so you cannot use global/static variables,
215 only stack variables and global_data
217 Non-SPL-specific notes:
218 - dram_init() is called to set up DRAM. If already done in SPL this
222 - you can override the entire board_init_f() function with your own
224 - preloader_console_init() can be called here in extremis
225 - should set up SDRAM, and anything needed to make the UART work
226 - there is no need to clear BSS, it will be done by crt0.S
227 - for specific scenarios on certain architectures an early BSS *can*
228 be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
229 of BSS prior to entering board_init_f()) but doing so is discouraged.
230 Instead it is strongly recommended to architect any code changes
231 or additions such to not depend on the availability of BSS during
232 board_init_f() as indicated in other sections of this README to
233 maintain compatibility and consistency across the entire code base.
234 - must return normally from this function (don't call board_init_r()
237 Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
238 this point the stack and global_data are relocated to below
239 CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
243 - purpose: main execution, common code
244 - global_data is available
246 - BSS is available, all static/global variables can be used
247 - execution eventually continues to main_loop()
249 Non-SPL-specific notes:
250 - U-Boot is relocated to the top of memory and is now running from
254 - stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
255 CONFIG_SYS_FSL_HAS_CCI400
257 Defined For SoC that has cache coherent interconnect
260 CONFIG_SYS_FSL_HAS_CCN504
262 Defined for SoC that has cache coherent interconnect CCN-504
264 The following options need to be configured:
266 - CPU Type: Define exactly one, e.g. CONFIG_MPC85XX.
268 - Board Type: Define exactly one, e.g. CONFIG_MPC8540ADS.
273 Specifies that the core is a 64-bit PowerPC implementation (implements
274 the "64" category of the Power ISA). This is necessary for ePAPR
275 compliance, among other possible reasons.
277 CONFIG_SYS_FSL_ERRATUM_A004510
279 Enables a workaround for erratum A004510. If set,
280 then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
281 CFG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
283 CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
284 CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
286 Defines one or two SoC revisions (low 8 bits of SVR)
287 for which the A004510 workaround should be applied.
289 The rest of SVR is either not relevant to the decision
290 of whether the erratum is present (e.g. p2040 versus
291 p2041) or is implied by the build target, which controls
292 whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
294 See Freescale App Note 4493 for more information about
297 CFG_SYS_FSL_CORENET_SNOOPVEC_COREONLY
299 This is the value to write into CCSR offset 0x18600
300 according to the A004510 workaround.
302 CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
303 Single Source Clock is clocking mode present in some of FSL SoC's.
304 In this mode, a single differential clock is used to supply
305 clocks to the sysclock, ddrclock and usbclock.
307 - Generic CPU options:
310 Freescale DDR driver in use. This type of DDR controller is
311 found in mpc83xx, mpc85xx as well as some ARM core SoCs.
314 Freescale DDR memory-mapped register base.
316 CONFIG_SYS_FSL_IFC_CLK_DIV
317 Defines divider of platform clock(clock input to IFC controller).
319 CONFIG_SYS_FSL_LBC_CLK_DIV
320 Defines divider of platform clock(clock input to eLBC controller).
322 CFG_SYS_FSL_DDR_SDRAM_BASE_PHY
323 Physical address from the view of DDR controllers. It is the
324 same as CFG_SYS_DDR_SDRAM_BASE for all Power SoCs. But
325 it could be different for ARM SoCs.
328 CONFIG_XWAY_SWAP_BYTES
330 Enable compilation of tools/xway-swap-bytes needed for Lantiq
331 XWAY SoCs for booting from NOR flash. The U-Boot image needs to
332 be swapped if a flash programmer is used.
335 CFG_SYS_EXCEPTION_VECTORS_HIGH
337 Select high exception vectors of the ARM core, e.g., do not
338 clear the V bit of the c1 register of CP15.
341 Generic timer clock source frequency.
343 COUNTER_FREQUENCY_REAL
344 Generic timer clock source frequency if the real clock is
345 different from COUNTER_FREQUENCY, and can only be determined
349 CONFIG_TEGRA_SUPPORT_NON_SECURE
351 Support executing U-Boot in non-secure (NS) mode. Certain
352 impossible actions will be skipped if the CPU is in NS mode,
353 such as ARM architectural timer initialization.
355 - Linux Kernel Interface:
358 New kernel versions are expecting firmware settings to be
359 passed using flattened device trees (based on open firmware
363 * New libfdt-based support
364 * Adds the "fdt" command
365 * The bootm command automatically updates the fdt
367 OF_TBCLK - The timebase frequency.
369 boards with QUICC Engines require OF_QE to set UCC MAC
374 U-Boot can detect if an IDE device is present or not.
375 If not, and this new config option is activated, U-Boot
376 removes the ATA node from the DTS before booting Linux,
377 so the Linux IDE driver does not probe the device and
378 crash. This is needed for buggy hardware (uc101) where
379 no pull down resistor is connected to the signal IDE5V_DD7.
381 - vxWorks boot parameters:
383 bootvx constructs a valid bootline using the following
384 environments variables: bootdev, bootfile, ipaddr, netmask,
385 serverip, gatewayip, hostname, othbootargs.
386 It loads the vxWorks image pointed bootfile.
388 Note: If a "bootargs" environment is defined, it will override
389 the defaults discussed just above.
391 - Cache Configuration for ARM:
392 CFG_SYS_PL310_BASE - Physical base address of PL310
393 controller register space
398 If you have Amba PrimeCell PL011 UARTs, set this variable to
399 the clock speed of the UARTs.
403 If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
404 define this to a list of base addresses for each (supported)
405 port. See e.g. include/configs/versatile.h
407 CONFIG_SERIAL_HW_FLOW_CONTROL
409 Define this variable to enable hw flow control in serial driver.
410 Current user of this option is drivers/serial/nsl16550.c driver
412 - Removal of commands
413 If no commands are needed to boot, you can disable
414 CONFIG_CMDLINE to remove them. In this case, the command line
415 will not be available, and when U-Boot wants to execute the
416 boot command (on start-up) it will call board_run_command()
417 instead. This can reduce image size significantly for very
418 simple boot procedures.
420 - Regular expression support:
422 If this variable is defined, U-Boot is linked against
423 the SLRE (Super Light Regular Expression) library,
424 which adds regex support to some commands, as for
425 example "env grep" and "setexpr".
428 CFG_SYS_WATCHDOG_FREQ
429 Some platforms automatically call WATCHDOG_RESET()
430 from the timer interrupt handler every
431 CFG_SYS_WATCHDOG_FREQ interrupts. If not set by the
432 board configuration file, a default of CONFIG_SYS_HZ/2
433 (i.e. 500) is used. Setting CFG_SYS_WATCHDOG_FREQ
434 to 0 disables calling WATCHDOG_RESET() from the timer
438 The CFG_SYS_I2C_PCA953X_WIDTH option specifies a list of
439 chip-ngpio pairs that tell the PCA953X driver the number of
440 pins supported by a particular chip.
442 Note that if the GPIO device uses I2C, then the I2C interface
443 must also be configured. See I2C Support, below.
446 When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
447 accesses and can checksum them or write a list of them out
448 to memory. See the 'iotrace' command for details. This is
449 useful for testing device drivers since it can confirm that
450 the driver behaves the same way before and after a code
451 change. Currently this is supported on sandbox and arm. To
452 add support for your architecture, add '#include <iotrace.h>'
453 to the bottom of arch/<arch>/include/asm/io.h and test.
455 Example output from the 'iotrace stats' command is below.
456 Note that if the trace buffer is exhausted, the checksum will
457 still continue to operate.
460 Start: 10000000 (buffer start address)
461 Size: 00010000 (buffer size)
462 Offset: 00000120 (current buffer offset)
463 Output: 10000120 (start + offset)
464 Count: 00000018 (number of trace records)
465 CRC32: 9526fb66 (CRC32 of all trace records)
469 When CONFIG_TIMESTAMP is selected, the timestamp
470 (date and time) of an image is printed by image
471 commands like bootm or iminfo. This option is
472 automatically enabled when you select CONFIG_CMD_DATE .
474 - Partition Labels (disklabels) Supported:
475 Zero or more of the following:
476 CONFIG_MAC_PARTITION Apple's MacOS partition table.
477 CONFIG_ISO_PARTITION ISO partition table, used on CDROM etc.
478 CONFIG_EFI_PARTITION GPT partition table, common when EFI is the
479 bootloader. Note 2TB partition limit; see
481 CONFIG_SCSI) you must configure support for at
482 least one non-MTD partition type as well.
484 - NETWORK Support (PCI):
486 Utility code for direct access to the SPI bus on Intel 8257x.
487 This does not do anything useful unless you set at least one
488 of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.
491 Support for National dp83815 chips.
494 Support for National dp8382[01] gigabit chips.
496 - NETWORK Support (other):
498 Support for the Calxeda XGMAC device
501 Support for SMSC's LAN91C96 chips.
503 CONFIG_LAN91C96_USE_32_BIT
504 Define this to enable 32 bit addressing
506 CFG_SYS_DAVINCI_EMAC_PHY_COUNT
507 Define this if you have more then 3 PHYs.
510 Support for Faraday's FTGMAC100 Gigabit SoC Ethernet
512 CONFIG_FTGMAC100_EGIGA
513 Define this to use GE link update with gigabit PHY.
514 Define this if FTGMAC100 is connected to gigabit PHY.
515 If your system has 10/100 PHY only, it might not occur
516 wrong behavior. Because PHY usually return timeout or
517 useless data when polling gigabit status and gigabit
518 control registers. This behavior won't affect the
519 correctnessof 10/100 link speed update.
522 Support for Renesas on-chip Ethernet controller
524 CFG_SH_ETHER_USE_PORT
525 Define the number of ports to be used
527 CFG_SH_ETHER_PHY_ADDR
528 Define the ETH PHY's address
530 CFG_SH_ETHER_CACHE_WRITEBACK
531 If this option is set, the driver enables cache flush.
537 CONFIG_TPM_TIS_INFINEON
538 Support for Infineon i2c bus TPM devices. Only one device
539 per system is supported at this time.
541 CONFIG_TPM_TIS_I2C_BURST_LIMITATION
542 Define the burst count bytes upper limit
545 Support for STMicroelectronics TPM devices. Requires DM_TPM support.
547 CONFIG_TPM_ST33ZP24_I2C
548 Support for STMicroelectronics ST33ZP24 I2C devices.
549 Requires TPM_ST33ZP24 and I2C.
551 CONFIG_TPM_ST33ZP24_SPI
552 Support for STMicroelectronics ST33ZP24 SPI devices.
553 Requires TPM_ST33ZP24 and SPI.
556 Support for Atmel TWI TPM device. Requires I2C support.
559 Support for generic parallel port TPM devices. Only one device
560 per system is supported at this time.
563 Define this to enable the TPM support library which provides
564 functional interfaces to some TPM commands.
565 Requires support for a TPM device.
567 CONFIG_TPM_AUTH_SESSIONS
568 Define this to enable authorized functions in the TPM library.
569 Requires CONFIG_TPM and CONFIG_SHA1.
572 At the moment only the UHCI host controller is
573 supported (PIP405, MIP405); define
574 CONFIG_USB_UHCI to enable it.
575 define CONFIG_USB_KEYBOARD to enable the USB Keyboard
576 and define CONFIG_USB_STORAGE to enable the USB
579 Supported are USB Keyboards and USB Floppy drives
582 CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
586 Define the below if you wish to use the USB console.
587 Once firmware is rebuilt from a serial console issue the
588 command "setenv stdin usbtty; setenv stdout usbtty" and
589 attach your USB cable. The Unix command "dmesg" should print
590 it has found a new device. The environment variable usbtty
591 can be set to gserial or cdc_acm to enable your device to
592 appear to a USB host as a Linux gserial device or a
593 Common Device Class Abstract Control Model serial device.
594 If you select usbtty = gserial you should be able to enumerate
596 # modprobe usbserial vendor=0xVendorID product=0xProductID
597 else if using cdc_acm, simply setting the environment
598 variable usbtty to be cdc_acm should suffice. The following
599 might be defined in YourBoardName.h
601 If you have a USB-IF assigned VendorID then you may wish to
602 define your own vendor specific values either in BoardName.h
603 or directly in usbd_vendor_info.h. If you don't define
604 CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
605 CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
606 should pretend to be a Linux device to it's target host.
608 CONFIG_USBD_MANUFACTURER
609 Define this string as the name of your company for
610 - CONFIG_USBD_MANUFACTURER "my company"
612 CONFIG_USBD_PRODUCT_NAME
613 Define this string as the name of your product
614 - CONFIG_USBD_PRODUCT_NAME "acme usb device"
617 Define this as your assigned Vendor ID from the USB
618 Implementors Forum. This *must* be a genuine Vendor ID
619 to avoid polluting the USB namespace.
620 - CONFIG_USBD_VENDORID 0xFFFF
622 CONFIG_USBD_PRODUCTID
623 Define this as the unique Product ID
625 - CONFIG_USBD_PRODUCTID 0xFFFF
627 - ULPI Layer Support:
628 The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
629 the generic ULPI layer. The generic layer accesses the ULPI PHY
630 via the platform viewport, so you need both the genric layer and
631 the viewport enabled. Currently only Chipidea/ARC based
632 viewport is supported.
633 To enable the ULPI layer support, define CONFIG_USB_ULPI and
634 CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
635 If your ULPI phy needs a different reference clock than the
636 standard 24 MHz then you have to define CFG_ULPI_REF_CLK to
637 the appropriate value in Hz.
641 Support for Renesas on-chip MMCIF controller
644 Define the base address of MMCIF registers
647 Define the clock frequency for MMCIF
649 - USB Device Firmware Update (DFU) class support:
651 This enables the USB portion of the DFU USB class
654 This enables support for exposing NAND devices via DFU.
657 This enables support for exposing RAM via DFU.
658 Note: DFU spec refer to non-volatile memory usage, but
659 allow usages beyond the scope of spec - here RAM usage,
660 one that would help mostly the developer.
662 CONFIG_SYS_DFU_DATA_BUF_SIZE
663 Dfu transfer uses a buffer before writing data to the
664 raw storage device. Make the size (in bytes) of this buffer
665 configurable. The size of this buffer is also configurable
666 through the "dfu_bufsiz" environment variable.
668 CONFIG_SYS_DFU_MAX_FILE_SIZE
669 When updating files rather than the raw storage device,
670 we use a static buffer to copy the file into and then write
671 the buffer once we've been given the whole file. Define
672 this to the maximum filesize (in bytes) for the buffer.
673 Default is 4 MiB if undefined.
675 DFU_DEFAULT_POLL_TIMEOUT
676 Poll timeout [ms], is the timeout a device can send to the
677 host. The host must wait for this timeout before sending
678 a subsequent DFU_GET_STATUS request to the device.
680 DFU_MANIFEST_POLL_TIMEOUT
681 Poll timeout [ms], which the device sends to the host when
682 entering dfuMANIFEST state. Host waits this timeout, before
683 sending again an USB request to the device.
686 See Kconfig help for available keyboard drivers.
689 CONFIG_PHY_CLOCK_FREQ (ppc4xx)
691 The clock frequency of the MII bus
693 CONFIG_PHY_CMD_DELAY (ppc4xx)
695 Some PHY like Intel LXT971A need extra delay after
696 command issued before MII status register can be read
698 - BOOTP Recovery Mode:
699 CONFIG_BOOTP_RANDOM_DELAY
701 If you have many targets in a network that try to
702 boot using BOOTP, you may want to avoid that all
703 systems send out BOOTP requests at precisely the same
704 moment (which would happen for instance at recovery
705 from a power failure, when all systems will try to
706 boot, thus flooding the BOOTP server. Defining
707 CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
708 inserted before sending out BOOTP requests. The
709 following delays are inserted then:
711 1st BOOTP request: delay 0 ... 1 sec
712 2nd BOOTP request: delay 0 ... 2 sec
713 3rd BOOTP request: delay 0 ... 4 sec
715 BOOTP requests: delay 0 ... 8 sec
717 CFG_BOOTP_ID_CACHE_SIZE
719 BOOTP packets are uniquely identified using a 32-bit ID. The
720 server will copy the ID from client requests to responses and
721 U-Boot will use this to determine if it is the destination of
722 an incoming response. Some servers will check that addresses
723 aren't in use before handing them out (usually using an ARP
724 ping) and therefore take up to a few hundred milliseconds to
725 respond. Network congestion may also influence the time it
726 takes for a response to make it back to the client. If that
727 time is too long, U-Boot will retransmit requests. In order
728 to allow earlier responses to still be accepted after these
729 retransmissions, U-Boot's BOOTP client keeps a small cache of
730 IDs. The CFG_BOOTP_ID_CACHE_SIZE controls the size of this
731 cache. The default is to keep IDs for up to four outstanding
732 requests. Increasing this will allow U-Boot to accept offers
733 from a BOOTP client in networks with unusually high latency.
735 - DHCP Advanced Options:
737 - Link-local IP address negotiation:
738 Negotiate with other link-local clients on the local network
739 for an address that doesn't require explicit configuration.
740 This is especially useful if a DHCP server cannot be guaranteed
741 to exist in all environments that the device must operate.
743 See doc/README.link-local for more information.
745 - MAC address from environment variables
747 FDT_SEQ_MACADDR_FROM_ENV
749 Fix-up device tree with MAC addresses fetched sequentially from
750 environment variables. This config work on assumption that
751 non-usable ethernet node of device-tree are either not present
752 or their status has been marked as "disabled".
757 The device id used in CDP trigger frames.
759 CONFIG_CDP_DEVICE_ID_PREFIX
761 A two character string which is prefixed to the MAC address
766 A printf format string which contains the ascii name of
767 the port. Normally is set to "eth%d" which sets
768 eth0 for the first Ethernet, eth1 for the second etc.
770 CONFIG_CDP_CAPABILITIES
772 A 32bit integer which indicates the device capabilities;
773 0x00000010 for a normal host which does not forwards.
777 An ascii string containing the version of the software.
781 An ascii string containing the name of the platform.
785 A 32bit integer sent on the trigger.
787 CONFIG_CDP_POWER_CONSUMPTION
789 A 16bit integer containing the power consumption of the
790 device in .1 of milliwatts.
792 CONFIG_CDP_APPLIANCE_VLAN_TYPE
794 A byte containing the id of the VLAN.
796 - Status LED: CONFIG_LED_STATUS
798 Several configurations allow to display the current
799 status using a LED. For instance, the LED will blink
800 fast while running U-Boot code, stop blinking as
801 soon as a reply to a BOOTP request was received, and
802 start blinking slow once the Linux kernel is running
803 (supported by a status LED driver in the Linux
804 kernel). Defining CONFIG_LED_STATUS enables this
809 CONFIG_LED_STATUS_GPIO
810 The status LED can be connected to a GPIO pin.
811 In such cases, the gpio_led driver can be used as a
812 status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
813 to include the gpio_led driver in the U-Boot binary.
815 CFG_GPIO_LED_INVERTED_TABLE
816 Some GPIO connected LEDs may have inverted polarity in which
817 case the GPIO high value corresponds to LED off state and
818 GPIO low value corresponds to LED on state.
819 In such cases CFG_GPIO_LED_INVERTED_TABLE may be defined
820 with a list of GPIO LEDs that have inverted polarity.
823 CFG_SYS_NUM_I2C_BUSES
824 Hold the number of i2c buses you want to use.
826 CFG_SYS_I2C_DIRECT_BUS
827 define this, if you don't use i2c muxes on your hardware.
828 if CFG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
832 define how many muxes are maximal consecutively connected
833 on one i2c bus. If you not use i2c muxes, omit this
837 hold a list of buses you want to use, only used if
838 CFG_SYS_I2C_DIRECT_BUS is not defined, for example
839 a board with CFG_SYS_I2C_MAX_HOPS = 1 and
840 CFG_SYS_NUM_I2C_BUSES = 9:
842 CFG_SYS_I2C_BUSES {{0, {I2C_NULL_HOP}}, \
843 {0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
844 {0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
845 {0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
846 {0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
847 {0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
848 {1, {I2C_NULL_HOP}}, \
849 {1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
850 {1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
854 bus 0 on adapter 0 without a mux
855 bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
856 bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
857 bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
858 bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
859 bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
860 bus 6 on adapter 1 without a mux
861 bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
862 bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2
864 If you do not have i2c muxes on your board, omit this define.
866 - Legacy I2C Support:
867 If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
868 then the following macros need to be defined (examples are
869 from include/configs/lwmon.h):
873 (Optional). Any commands necessary to enable the I2C
874 controller or configure ports.
876 eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |= PB_SCL)
880 The code necessary to make the I2C data line active
881 (driven). If the data line is open collector, this
884 eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |= PB_SDA)
888 The code necessary to make the I2C data line tri-stated
889 (inactive). If the data line is open collector, this
892 eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)
896 Code that returns true if the I2C data line is high,
899 eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)
903 If <bit> is true, sets the I2C data line high. If it
904 is false, it clears it (low).
906 eg: #define I2C_SDA(bit) \
907 if(bit) immr->im_cpm.cp_pbdat |= PB_SDA; \
908 else immr->im_cpm.cp_pbdat &= ~PB_SDA
912 If <bit> is true, sets the I2C clock line high. If it
913 is false, it clears it (low).
915 eg: #define I2C_SCL(bit) \
916 if(bit) immr->im_cpm.cp_pbdat |= PB_SCL; \
917 else immr->im_cpm.cp_pbdat &= ~PB_SCL
921 This delay is invoked four times per clock cycle so this
922 controls the rate of data transfer. The data rate thus
923 is 1 / (I2C_DELAY * 4). Often defined to be something
926 #define I2C_DELAY udelay(2)
928 CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
930 If your arch supports the generic GPIO framework (asm/gpio.h),
931 then you may alternatively define the two GPIOs that are to be
932 used as SCL / SDA. Any of the previous I2C_xxx macros will
933 have GPIO-based defaults assigned to them as appropriate.
935 You should define these to the GPIO value as given directly to
936 the generic GPIO functions.
940 This option allows the use of multiple I2C buses, each of which
941 must have a controller. At any point in time, only one bus is
942 active. To switch to a different bus, use the 'i2c dev' command.
943 Note that bus numbering is zero-based.
947 This option specifies a list of I2C devices that will be skipped
948 when the 'i2c probe' command is issued.
951 #define CFG_SYS_I2C_NOPROBES {0x50,0x68}
953 will skip addresses 0x50 and 0x68 on a board with one I2C bus
957 If defined, then this indicates the I2C bus number for the RTC.
958 If not defined, then U-Boot assumes that RTC is on I2C bus 0.
960 CONFIG_SOFT_I2C_READ_REPEATED_START
962 defining this will force the i2c_read() function in
963 the soft_i2c driver to perform an I2C repeated start
964 between writing the address pointer and reading the
965 data. If this define is omitted the default behaviour
966 of doing a stop-start sequence will be used. Most I2C
967 devices can use either method, but some require one or
970 - SPI Support: CONFIG_SPI
972 Enables SPI driver (so far only tested with
973 SPI EEPROM, also an instance works with Crystal A/D and
974 D/As on the SACSng board)
977 Timeout for waiting until spi transfer completed.
978 default: (CONFIG_SYS_HZ/100) /* 10 ms */
980 - FPGA Support: CONFIG_FPGA
982 Enables FPGA subsystem.
986 Enables support for specific chip vendors.
991 Enables support for FPGA family.
992 (SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
994 CONFIG_SYS_FPGA_CHECK_BUSY
996 Enable checks on FPGA configuration interface busy
997 status by the configuration function. This option
998 will require a board or device specific function to
1003 If defined, a function that provides delays in the FPGA
1004 configuration driver.
1006 CFG_SYS_FPGA_CHECK_ERROR
1008 Check for configuration errors during FPGA bitfile
1009 loading. For example, abort during Virtex II
1010 configuration if the INIT_B line goes low (which
1011 indicated a CRC error).
1013 CFG_SYS_FPGA_WAIT_INIT
1015 Maximum time to wait for the INIT_B line to de-assert
1016 after PROB_B has been de-asserted during a Virtex II
1017 FPGA configuration sequence. The default time is 500
1020 CFG_SYS_FPGA_WAIT_BUSY
1022 Maximum time to wait for BUSY to de-assert during
1023 Virtex II FPGA configuration. The default is 5 ms.
1025 CFG_SYS_FPGA_WAIT_CONFIG
1027 Time to wait after FPGA configuration. The default is
1030 - Vendor Parameter Protection:
1032 U-Boot considers the values of the environment
1033 variables "serial#" (Board Serial Number) and
1034 "ethaddr" (Ethernet Address) to be parameters that
1035 are set once by the board vendor / manufacturer, and
1036 protects these variables from casual modification by
1037 the user. Once set, these variables are read-only,
1038 and write or delete attempts are rejected. You can
1039 change this behaviour:
1041 If CONFIG_ENV_OVERWRITE is #defined in your config
1042 file, the write protection for vendor parameters is
1043 completely disabled. Anybody can change or delete
1046 The same can be accomplished in a more flexible way
1047 for any variable by configuring the type of access
1048 to allow for those variables in the ".flags" variable
1049 or define CFG_ENV_FLAGS_LIST_STATIC.
1054 Define this variable to enable the reservation of
1055 "protected RAM", i. e. RAM which is not overwritten
1056 by U-Boot. Define CFG_PRAM to hold the number of
1057 kB you want to reserve for pRAM. You can overwrite
1058 this default value by defining an environment
1059 variable "pram" to the number of kB you want to
1060 reserve. Note that the board info structure will
1061 still show the full amount of RAM. If pRAM is
1062 reserved, a new environment variable "mem" will
1063 automatically be defined to hold the amount of
1064 remaining RAM in a form that can be passed as boot
1065 argument to Linux, for instance like that:
1067 setenv bootargs ... mem=\${mem}
1070 This way you can tell Linux not to use this memory,
1071 either, which results in a memory region that will
1072 not be affected by reboots.
1074 *WARNING* If your board configuration uses automatic
1075 detection of the RAM size, you must make sure that
1076 this memory test is non-destructive. So far, the
1077 following board configurations are known to be
1080 IVMS8, IVML24, SPD8xx,
1081 HERMES, IP860, RPXlite, LWMON,
1087 In the current implementation, the local variables
1088 space and global environment variables space are
1089 separated. Local variables are those you define by
1090 simply typing `name=value'. To access a local
1091 variable later on, you have write `$name' or
1092 `${name}'; to execute the contents of a variable
1093 directly type `$name' at the command prompt.
1095 Global environment variables are those you use
1096 setenv/printenv to work with. To run a command stored
1097 in such a variable, you need to use the run command,
1098 and you must not use the '$' sign to access them.
1100 To store commands and special characters in a
1101 variable, please use double quotation marks
1102 surrounding the whole text of the variable, instead
1103 of the backslashes before semicolons and special
1106 - Default Environment:
1107 CFG_EXTRA_ENV_SETTINGS
1109 Define this to contain any number of null terminated
1110 strings (variable = value pairs) that will be part of
1111 the default environment compiled into the boot image.
1113 For example, place something like this in your
1114 board's config file:
1116 #define CFG_EXTRA_ENV_SETTINGS \
1120 Warning: This method is based on knowledge about the
1121 internal format how the environment is stored by the
1122 U-Boot code. This is NOT an official, exported
1123 interface! Although it is unlikely that this format
1124 will change soon, there is no guarantee either.
1125 You better know what you are doing here.
1127 Note: overly (ab)use of the default environment is
1128 discouraged. Make sure to check other ways to preset
1129 the environment like the "source" command or the
1132 CONFIG_DELAY_ENVIRONMENT
1134 Normally the environment is loaded when the board is
1135 initialised so that it is available to U-Boot. This inhibits
1136 that so that the environment is not available until
1137 explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL
1138 this is instead controlled by the value of
1139 /config/load-environment.
1141 - Automatic software updates via TFTP server
1143 CONFIG_UPDATE_TFTP_CNT_MAX
1144 CONFIG_UPDATE_TFTP_MSEC_MAX
1146 These options enable and control the auto-update feature;
1147 for a more detailed description refer to doc/README.update.
1149 - MTD Support (mtdparts command, UBI support)
1150 CONFIG_MTD_UBI_WL_THRESHOLD
1151 This parameter defines the maximum difference between the highest
1152 erase counter value and the lowest erase counter value of eraseblocks
1153 of UBI devices. When this threshold is exceeded, UBI starts performing
1154 wear leveling by means of moving data from eraseblock with low erase
1155 counter to eraseblocks with high erase counter.
1157 The default value should be OK for SLC NAND flashes, NOR flashes and
1158 other flashes which have eraseblock life-cycle 100000 or more.
1159 However, in case of MLC NAND flashes which typically have eraseblock
1160 life-cycle less than 10000, the threshold should be lessened (e.g.,
1161 to 128 or 256, although it does not have to be power of 2).
1165 CONFIG_MTD_UBI_BEB_LIMIT
1166 This option specifies the maximum bad physical eraseblocks UBI
1167 expects on the MTD device (per 1024 eraseblocks). If the
1168 underlying flash does not admit of bad eraseblocks (e.g. NOR
1169 flash), this value is ignored.
1171 NAND datasheets often specify the minimum and maximum NVM
1172 (Number of Valid Blocks) for the flashes' endurance lifetime.
1173 The maximum expected bad eraseblocks per 1024 eraseblocks
1174 then can be calculated as "1024 * (1 - MinNVB / MaxNVB)",
1175 which gives 20 for most NANDs (MaxNVB is basically the total
1176 count of eraseblocks on the chip).
1178 To put it differently, if this value is 20, UBI will try to
1179 reserve about 1.9% of physical eraseblocks for bad blocks
1180 handling. And that will be 1.9% of eraseblocks on the entire
1181 NAND chip, not just the MTD partition UBI attaches. This means
1182 that if you have, say, a NAND flash chip admits maximum 40 bad
1183 eraseblocks, and it is split on two MTD partitions of the same
1184 size, UBI will reserve 40 eraseblocks when attaching a
1189 CONFIG_MTD_UBI_FASTMAP
1190 Fastmap is a mechanism which allows attaching an UBI device
1191 in nearly constant time. Instead of scanning the whole MTD device it
1192 only has to locate a checkpoint (called fastmap) on the device.
1193 The on-flash fastmap contains all information needed to attach
1194 the device. Using fastmap makes only sense on large devices where
1195 attaching by scanning takes long. UBI will not automatically install
1196 a fastmap on old images, but you can set the UBI parameter
1197 CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note
1198 that fastmap-enabled images are still usable with UBI implementations
1199 without fastmap support. On typical flash devices the whole fastmap
1200 fits into one PEB. UBI will reserve PEBs to hold two fastmaps.
1202 CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT
1203 Set this parameter to enable fastmap automatically on images
1207 CONFIG_MTD_UBI_FM_DEBUG
1208 Enable UBI fastmap debug
1213 Enable building of SPL globally.
1215 CONFIG_SPL_PANIC_ON_RAW_IMAGE
1216 When defined, SPL will panic() if the image it has
1217 loaded does not have a signature.
1218 Defining this is useful when code which loads images
1219 in SPL cannot guarantee that absolutely all read errors
1221 An example is the LPC32XX MLC NAND driver, which will
1222 consider that a completely unreadable NAND block is bad,
1223 and thus should be skipped silently.
1225 CONFIG_SPL_DISPLAY_PRINT
1226 For ARM, enable an optional function to print more information
1227 about the running system.
1229 CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
1230 Set this for NAND SPL on PPC mpc83xx targets, so that
1231 start.S waits for the rest of the SPL to load before
1232 continuing (the hardware starts execution after just
1233 loading the first page rather than the full 4K).
1236 Support for a lightweight UBI (fastmap) scanner and
1239 CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
1240 CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
1241 CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
1242 CFG_SYS_NAND_ECCPOS, CFG_SYS_NAND_ECCSIZE,
1243 CFG_SYS_NAND_ECCBYTES
1244 Defines the size and behavior of the NAND that SPL uses
1247 CFG_SYS_NAND_U_BOOT_DST
1248 Location in memory to load U-Boot to
1250 CFG_SYS_NAND_U_BOOT_SIZE
1251 Size of image to load
1253 CFG_SYS_NAND_U_BOOT_START
1254 Entry point in loaded image to jump to
1256 CONFIG_SPL_RAM_DEVICE
1257 Support for running image already present in ram, in SPL binary
1259 CONFIG_SPL_FIT_PRINT
1260 Printing information about a FIT image adds quite a bit of
1261 code to SPL. So this is normally disabled in SPL. Use this
1262 option to re-enable it. This will affect the output of the
1263 bootm command when booting a FIT image.
1265 - Interrupt support (PPC):
1267 There are common interrupt_init() and timer_interrupt()
1268 for all PPC archs. interrupt_init() calls interrupt_init_cpu()
1269 for CPU specific initialization. interrupt_init_cpu()
1270 should set decrementer_count to appropriate value. If
1271 CPU resets decrementer automatically after interrupt
1272 (ppc4xx) it should set decrementer_count to zero.
1273 timer_interrupt() calls timer_interrupt_cpu() for CPU
1274 specific handling. If board has watchdog / status_led
1275 / other_activity_monitor it works automatically from
1276 general timer_interrupt().
1279 Board initialization settings:
1280 ------------------------------
1282 During Initialization u-boot calls a number of board specific functions
1283 to allow the preparation of board specific prerequisites, e.g. pin setup
1284 before drivers are initialized. To enable these callbacks the
1285 following configuration macros have to be defined. Currently this is
1286 architecture specific, so please check arch/your_architecture/lib/board.c
1287 typically in board_init_f() and board_init_r().
1289 - CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
1290 - CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
1291 - CONFIG_BOARD_LATE_INIT: Call board_late_init()
1293 Configuration Settings:
1294 -----------------------
1296 - MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.
1297 Optionally it can be defined to support 64-bit memory commands.
1299 - CONFIG_SYS_LONGHELP: Defined when you want long help messages included;
1300 undefine this when you're short of memory.
1302 - CFG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default
1303 width of the commands listed in the 'help' command output.
1305 - CONFIG_SYS_PROMPT: This is what U-Boot prints on the console to
1306 prompt for user input.
1308 - CFG_SYS_BAUDRATE_TABLE:
1309 List of legal baudrate settings for this board.
1311 - CFG_SYS_MEM_RESERVE_SECURE
1312 Only implemented for ARMv8 for now.
1313 If defined, the size of CFG_SYS_MEM_RESERVE_SECURE memory
1314 is substracted from total RAM and won't be reported to OS.
1315 This memory can be used as secure memory. A variable
1316 gd->arch.secure_ram is used to track the location. In systems
1317 the RAM base is not zero, or RAM is divided into banks,
1318 this variable needs to be recalcuated to get the address.
1320 - CFG_SYS_SDRAM_BASE:
1321 Physical start address of SDRAM. _Must_ be 0 here.
1323 - CFG_SYS_FLASH_BASE:
1324 Physical start address of Flash memory.
1326 - CONFIG_SYS_MALLOC_LEN:
1327 Size of DRAM reserved for malloc() use.
1329 - CONFIG_SYS_MALLOC_F_LEN
1330 Size of the malloc() pool for use before relocation. If
1331 this is defined, then a very simple malloc() implementation
1332 will become available before relocation. The address is just
1333 below the global data, and the stack is moved down to make
1336 This feature allocates regions with increasing addresses
1337 within the region. calloc() is supported, but realloc()
1338 is not available. free() is supported but does nothing.
1339 The memory will be freed (or in fact just forgotten) when
1340 U-Boot relocates itself.
1342 - CONFIG_SYS_MALLOC_SIMPLE
1343 Provides a simple and small malloc() and calloc() for those
1344 boards which do not use the full malloc in SPL (which is
1345 enabled with CONFIG_SYS_SPL_MALLOC).
1347 - CFG_SYS_BOOTMAPSZ:
1348 Maximum size of memory mapped by the startup code of
1349 the Linux kernel; all data that must be processed by
1350 the Linux kernel (bd_info, boot arguments, FDT blob if
1351 used) must be put below this limit, unless "bootm_low"
1352 environment variable is defined and non-zero. In such case
1353 all data for the Linux kernel must be between "bootm_low"
1354 and "bootm_low" + CFG_SYS_BOOTMAPSZ. The environment
1355 variable "bootm_mapsize" will override the value of
1356 CFG_SYS_BOOTMAPSZ. If CFG_SYS_BOOTMAPSZ is undefined,
1357 then the value in "bootm_size" will be used instead.
1359 - CONFIG_SYS_BOOT_GET_CMDLINE:
1360 Enables allocating and saving kernel cmdline in space between
1361 "bootm_low" and "bootm_low" + BOOTMAPSZ.
1363 - CONFIG_SYS_BOOT_GET_KBD:
1364 Enables allocating and saving a kernel copy of the bd_info in
1365 space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
1367 - CONFIG_SYS_FLASH_PROTECTION
1368 If defined, hardware flash sectors protection is used
1369 instead of U-Boot software protection.
1371 - CONFIG_SYS_FLASH_CFI:
1372 Define if the flash driver uses extra elements in the
1373 common flash structure for storing flash geometry.
1375 - CONFIG_FLASH_CFI_DRIVER
1376 This option also enables the building of the cfi_flash driver
1377 in the drivers directory
1379 - CONFIG_FLASH_CFI_MTD
1380 This option enables the building of the cfi_mtd driver
1381 in the drivers directory. The driver exports CFI flash
1384 - CONFIG_SYS_FLASH_USE_BUFFER_WRITE
1385 Use buffered writes to flash.
1387 - CONFIG_ENV_FLAGS_LIST_DEFAULT
1388 - CFG_ENV_FLAGS_LIST_STATIC
1389 Enable validation of the values given to environment variables when
1390 calling env set. Variables can be restricted to only decimal,
1391 hexadecimal, or boolean. If CONFIG_CMD_NET is also defined,
1392 the variables can also be restricted to IP address or MAC address.
1394 The format of the list is:
1395 type_attribute = [s|d|x|b|i|m]
1396 access_attribute = [a|r|o|c]
1397 attributes = type_attribute[access_attribute]
1398 entry = variable_name[:attributes]
1401 The type attributes are:
1402 s - String (default)
1405 b - Boolean ([1yYtT|0nNfF])
1409 The access attributes are:
1415 - CONFIG_ENV_FLAGS_LIST_DEFAULT
1416 Define this to a list (string) to define the ".flags"
1417 environment variable in the default or embedded environment.
1419 - CFG_ENV_FLAGS_LIST_STATIC
1420 Define this to a list (string) to define validation that
1421 should be done if an entry is not found in the ".flags"
1422 environment variable. To override a setting in the static
1423 list, simply add an entry for the same variable name to the
1426 If CONFIG_REGEX is defined, the variable_name above is evaluated as a
1427 regular expression. This allows multiple variables to define the same
1428 flags without explicitly listing them for each variable.
1430 The following definitions that deal with the placement and management
1431 of environment data (variable area); in general, we support the
1432 following configurations:
1434 BE CAREFUL! The first access to the environment happens quite early
1435 in U-Boot initialization (when we try to get the setting of for the
1436 console baudrate). You *MUST* have mapped your NVRAM area then, or
1439 Please note that even with NVRAM we still use a copy of the
1440 environment in RAM: we could work on NVRAM directly, but we want to
1441 keep settings there always unmodified except somebody uses "saveenv"
1442 to save the current settings.
1444 BE CAREFUL! For some special cases, the local device can not use
1445 "saveenv" command. For example, the local device will get the
1446 environment stored in a remote NOR flash by SRIO or PCIE link,
1447 but it can not erase, write this NOR flash by SRIO or PCIE interface.
1449 - CONFIG_NAND_ENV_DST
1451 Defines address in RAM to which the nand_spl code should copy the
1452 environment. If redundant environment is used, it will be copied to
1453 CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.
1455 Please note that the environment is read-only until the monitor
1456 has been relocated to RAM and a RAM copy of the environment has been
1457 created; also, when using EEPROM you will have to use env_get_f()
1458 until then to read environment variables.
1460 The environment is protected by a CRC32 checksum. Before the monitor
1461 is relocated into RAM, as a result of a bad CRC you will be working
1462 with the compiled-in default environment - *silently*!!! [This is
1463 necessary, because the first environment variable we need is the
1464 "baudrate" setting for the console - if we have a bad CRC, we don't
1465 have any device yet where we could complain.]
1467 Note: once the monitor has been relocated, then it will complain if
1468 the default environment is used; a new CRC is computed as soon as you
1469 use the "saveenv" command to store a valid environment.
1471 - CONFIG_SYS_FAULT_MII_ADDR:
1472 MII address of the PHY to check for the Ethernet link state.
1474 - CONFIG_DISPLAY_BOARDINFO
1475 Display information about the board that U-Boot is running on
1476 when U-Boot starts up. The board function checkboard() is called
1479 - CONFIG_DISPLAY_BOARDINFO_LATE
1480 Similar to the previous option, but display this information
1481 later, once stdio is running and output goes to the LCD, if
1484 Low Level (hardware related) configuration options:
1485 ---------------------------------------------------
1487 - CONFIG_SYS_CACHELINE_SIZE:
1488 Cache Line Size of the CPU.
1490 - CONFIG_SYS_CCSRBAR_DEFAULT:
1491 Default (power-on reset) physical address of CCSR on Freescale
1495 Virtual address of CCSR. On a 32-bit build, this is typically
1496 the same value as CONFIG_SYS_CCSRBAR_DEFAULT.
1498 - CFG_SYS_CCSRBAR_PHYS:
1499 Physical address of CCSR. CCSR can be relocated to a new
1500 physical address, if desired. In this case, this macro should
1501 be set to that address. Otherwise, it should be set to the
1502 same value as CONFIG_SYS_CCSRBAR_DEFAULT. For example, CCSR
1503 is typically relocated on 36-bit builds. It is recommended
1504 that this macro be defined via the _HIGH and _LOW macros:
1506 #define CFG_SYS_CCSRBAR_PHYS ((CFG_SYS_CCSRBAR_PHYS_HIGH
1507 * 1ull) << 32 | CFG_SYS_CCSRBAR_PHYS_LOW)
1509 - CFG_SYS_CCSRBAR_PHYS_HIGH:
1510 Bits 33-36 of CFG_SYS_CCSRBAR_PHYS. This value is typically
1511 either 0 (32-bit build) or 0xF (36-bit build). This macro is
1512 used in assembly code, so it must not contain typecasts or
1513 integer size suffixes (e.g. "ULL").
1515 - CFG_SYS_CCSRBAR_PHYS_LOW:
1516 Lower 32-bits of CFG_SYS_CCSRBAR_PHYS. This macro is
1517 used in assembly code, so it must not contain typecasts or
1518 integer size suffixes (e.g. "ULL").
1520 - CONFIG_SYS_IMMR: Physical address of the Internal Memory.
1521 DO NOT CHANGE unless you know exactly what you're
1522 doing! (11-4) [MPC8xx systems only]
1524 - CFG_SYS_INIT_RAM_ADDR:
1526 Start address of memory area that can be used for
1527 initial data and stack; please note that this must be
1528 writable memory that is working WITHOUT special
1529 initialization, i. e. you CANNOT use normal RAM which
1530 will become available only after programming the
1531 memory controller and running certain initialization
1534 U-Boot uses the following memory types:
1535 - MPC8xx: IMMR (internal memory of the CPU)
1537 - CONFIG_SYS_SCCR: System Clock and reset Control Register (15-27)
1539 - CONFIG_SYS_OR_TIMING_SDRAM:
1542 - CONFIG_SYS_SRIOn_MEM_VIRT:
1543 Virtual Address of SRIO port 'n' memory region
1545 - CONFIG_SYS_SRIOn_MEM_PHYxS:
1546 Physical Address of SRIO port 'n' memory region
1548 - CONFIG_SYS_SRIOn_MEM_SIZE:
1549 Size of SRIO port 'n' memory region
1551 - CONFIG_SYS_NAND_BUSWIDTH_16BIT
1552 Defined to tell the NAND controller that the NAND chip is using
1554 Not all NAND drivers use this symbol.
1555 Example of drivers that use it:
1556 - drivers/mtd/nand/raw/ndfc.c
1557 - drivers/mtd/nand/raw/mxc_nand.c
1559 - CONFIG_SYS_NDFC_EBC0_CFG
1560 Sets the EBC0_CFG register for the NDFC. If not defined
1561 a default value will be used.
1563 - CONFIG_SYS_SPD_BUS_NUM
1564 If SPD EEPROM is on an I2C bus other than the first
1565 one, specify here. Note that the value must resolve
1566 to something your driver can deal with.
1568 - CONFIG_FSL_DDR_INTERACTIVE
1569 Enable interactive DDR debugging. See doc/README.fsl-ddr.
1571 - CONFIG_FSL_DDR_SYNC_REFRESH
1572 Enable sync of refresh for multiple controllers.
1574 - CONFIG_FSL_DDR_BIST
1575 Enable built-in memory test for Freescale DDR controllers.
1578 Enable RMII mode for all FECs.
1579 Note that this is a global option, we can't
1580 have one FEC in standard MII mode and another in RMII mode.
1582 - CONFIG_CRC32_VERIFY
1583 Add a verify option to the crc32 command.
1586 => crc32 -v <address> <count> <crc32>
1588 Where address/count indicate a memory area
1589 and crc32 is the correct crc32 which the
1593 Add the "loopw" memory command. This only takes effect if
1594 the memory commands are activated globally (CONFIG_CMD_MEMORY).
1596 - CONFIG_CMD_MX_CYCLIC
1597 Add the "mdc" and "mwc" memory commands. These are cyclic
1602 This command will print 4 bytes (10,11,12,13) each 500 ms.
1604 => mwc.l 100 12345678 10
1605 This command will write 12345678 to address 100 all 10 ms.
1607 This only takes effect if the memory commands are activated
1608 globally (CONFIG_CMD_MEMORY).
1611 Set when the currently-running compilation is for an artifact
1612 that will end up in the SPL (as opposed to the TPL or U-Boot
1613 proper). Code that needs stage-specific behavior should check
1617 Set when the currently-running compilation is for an artifact
1618 that will end up in the TPL (as opposed to the SPL or U-Boot
1619 proper). Code that needs stage-specific behavior should check
1622 - CONFIG_ARCH_MAP_SYSMEM
1623 Generally U-Boot (and in particular the md command) uses
1624 effective address. It is therefore not necessary to regard
1625 U-Boot address as virtual addresses that need to be translated
1626 to physical addresses. However, sandbox requires this, since
1627 it maintains its own little RAM buffer which contains all
1628 addressable memory. This option causes some memory accesses
1629 to be mapped through map_sysmem() / unmap_sysmem().
1631 - CONFIG_X86_RESET_VECTOR
1632 If defined, the x86 reset vector code is included. This is not
1633 needed when U-Boot is running from Coreboot.
1635 Freescale QE/FMAN Firmware Support:
1636 -----------------------------------
1638 The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the
1639 loading of "firmware", which is encoded in the QE firmware binary format.
1640 This firmware often needs to be loaded during U-Boot booting, so macros
1641 are used to identify the storage device (NOR flash, SPI, etc) and the address
1644 - CONFIG_SYS_FMAN_FW_ADDR
1645 The address in the storage device where the FMAN microcode is located. The
1646 meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
1649 - CONFIG_SYS_QE_FW_ADDR
1650 The address in the storage device where the QE microcode is located. The
1651 meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
1654 - CONFIG_SYS_QE_FMAN_FW_LENGTH
1655 The maximum possible size of the firmware. The firmware binary format
1656 has a field that specifies the actual size of the firmware, but it
1657 might not be possible to read any part of the firmware unless some
1658 local storage is allocated to hold the entire firmware first.
1660 - CONFIG_SYS_QE_FMAN_FW_IN_NOR
1661 Specifies that QE/FMAN firmware is located in NOR flash, mapped as
1662 normal addressable memory via the LBC. CONFIG_SYS_FMAN_FW_ADDR is the
1663 virtual address in NOR flash.
1665 - CONFIG_SYS_QE_FMAN_FW_IN_NAND
1666 Specifies that QE/FMAN firmware is located in NAND flash.
1667 CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.
1669 - CONFIG_SYS_QE_FMAN_FW_IN_MMC
1670 Specifies that QE/FMAN firmware is located on the primary SD/MMC
1671 device. CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.
1673 - CONFIG_SYS_QE_FMAN_FW_IN_REMOTE
1674 Specifies that QE/FMAN firmware is located in the remote (master)
1675 memory space. CONFIG_SYS_FMAN_FW_ADDR is a virtual address which
1676 can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound
1677 window->master inbound window->master LAW->the ucode address in
1678 master's memory space.
1680 Freescale Layerscape Management Complex Firmware Support:
1681 ---------------------------------------------------------
1682 The Freescale Layerscape Management Complex (MC) supports the loading of
1684 This firmware often needs to be loaded during U-Boot booting, so macros
1685 are used to identify the storage device (NOR flash, SPI, etc) and the address
1688 - CONFIG_FSL_MC_ENET
1689 Enable the MC driver for Layerscape SoCs.
1691 Freescale Layerscape Debug Server Support:
1692 -------------------------------------------
1693 The Freescale Layerscape Debug Server Support supports the loading of
1694 "Debug Server firmware" and triggering SP boot-rom.
1695 This firmware often needs to be loaded during U-Boot booting.
1697 - CONFIG_SYS_MC_RSV_MEM_ALIGN
1698 Define alignment of reserved memory MC requires
1701 Building the Software:
1702 ======================
1704 Building U-Boot has been tested in several native build environments
1705 and in many different cross environments. Of course we cannot support
1706 all possibly existing versions of cross development tools in all
1707 (potentially obsolete) versions. In case of tool chain problems we
1708 recommend to use the ELDK (see https://www.denx.de/wiki/DULG/ELDK)
1709 which is extensively used to build and test U-Boot.
1711 If you are not using a native environment, it is assumed that you
1712 have GNU cross compiling tools available in your path. In this case,
1713 you must set the environment variable CROSS_COMPILE in your shell.
1714 Note that no changes to the Makefile or any other source files are
1715 necessary. For example using the ELDK on a 4xx CPU, please enter:
1717 $ CROSS_COMPILE=ppc_4xx-
1718 $ export CROSS_COMPILE
1720 U-Boot is intended to be simple to build. After installing the
1721 sources you must configure U-Boot for one specific board type. This
1726 where "NAME_defconfig" is the name of one of the existing configu-
1727 rations; see configs/*_defconfig for supported names.
1729 Note: for some boards special configuration names may exist; check if
1730 additional information is available from the board vendor; for
1731 instance, the TQM823L systems are available without (standard)
1732 or with LCD support. You can select such additional "features"
1733 when choosing the configuration, i. e.
1735 make TQM823L_defconfig
1736 - will configure for a plain TQM823L, i. e. no LCD support
1738 make TQM823L_LCD_defconfig
1739 - will configure for a TQM823L with U-Boot console on LCD
1744 Finally, type "make all", and you should get some working U-Boot
1745 images ready for download to / installation on your system:
1747 - "u-boot.bin" is a raw binary image
1748 - "u-boot" is an image in ELF binary format
1749 - "u-boot.srec" is in Motorola S-Record format
1751 By default the build is performed locally and the objects are saved
1752 in the source directory. One of the two methods can be used to change
1753 this behavior and build U-Boot to some external directory:
1755 1. Add O= to the make command line invocations:
1757 make O=/tmp/build distclean
1758 make O=/tmp/build NAME_defconfig
1759 make O=/tmp/build all
1761 2. Set environment variable KBUILD_OUTPUT to point to the desired location:
1763 export KBUILD_OUTPUT=/tmp/build
1768 Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
1771 User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by
1772 setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.
1773 For example to treat all compiler warnings as errors:
1775 make KCFLAGS=-Werror
1777 Please be aware that the Makefiles assume you are using GNU make, so
1778 for instance on NetBSD you might need to use "gmake" instead of
1782 If the system board that you have is not listed, then you will need
1783 to port U-Boot to your hardware platform. To do this, follow these
1786 1. Create a new directory to hold your board specific code. Add any
1787 files you need. In your board directory, you will need at least
1788 the "Makefile" and a "<board>.c".
1789 2. Create a new configuration file "include/configs/<board>.h" for
1791 3. If you're porting U-Boot to a new CPU, then also create a new
1792 directory to hold your CPU specific code. Add any files you need.
1793 4. Run "make <board>_defconfig" with your new name.
1794 5. Type "make", and you should get a working "u-boot.srec" file
1795 to be installed on your target system.
1796 6. Debug and solve any problems that might arise.
1797 [Of course, this last step is much harder than it sounds.]
1800 Testing of U-Boot Modifications, Ports to New Hardware, etc.:
1801 ==============================================================
1803 If you have modified U-Boot sources (for instance added a new board
1804 or support for new devices, a new CPU, etc.) you are expected to
1805 provide feedback to the other developers. The feedback normally takes
1806 the form of a "patch", i.e. a context diff against a certain (latest
1807 official or latest in the git repository) version of U-Boot sources.
1809 But before you submit such a patch, please verify that your modifi-
1810 cation did not break existing code. At least make sure that *ALL* of
1811 the supported boards compile WITHOUT ANY compiler warnings. To do so,
1812 just run the buildman script (tools/buildman/buildman), which will
1813 configure and build U-Boot for ALL supported system. Be warned, this
1814 will take a while. Please see the buildman README, or run 'buildman -H'
1818 See also "U-Boot Porting Guide" below.
1821 Monitor Commands - Overview:
1822 ============================
1824 go - start application at address 'addr'
1825 run - run commands in an environment variable
1826 bootm - boot application image from memory
1827 bootp - boot image via network using BootP/TFTP protocol
1828 bootz - boot zImage from memory
1829 tftpboot- boot image via network using TFTP protocol
1830 and env variables "ipaddr" and "serverip"
1831 (and eventually "gatewayip")
1832 tftpput - upload a file via network using TFTP protocol
1833 rarpboot- boot image via network using RARP/TFTP protocol
1834 diskboot- boot from IDE devicebootd - boot default, i.e., run 'bootcmd'
1835 loads - load S-Record file over serial line
1836 loadb - load binary file over serial line (kermit mode)
1837 loadm - load binary blob from source address to destination address
1839 mm - memory modify (auto-incrementing)
1840 nm - memory modify (constant address)
1841 mw - memory write (fill)
1844 cmp - memory compare
1845 crc32 - checksum calculation
1846 i2c - I2C sub-system
1847 sspi - SPI utility commands
1848 base - print or set address offset
1849 printenv- print environment variables
1850 pwm - control pwm channels
1851 setenv - set environment variables
1852 saveenv - save environment variables to persistent storage
1853 protect - enable or disable FLASH write protection
1854 erase - erase FLASH memory
1855 flinfo - print FLASH memory information
1856 nand - NAND memory operations (see doc/README.nand)
1857 bdinfo - print Board Info structure
1858 iminfo - print header information for application image
1859 coninfo - print console devices and informations
1860 ide - IDE sub-system
1861 loop - infinite loop on address range
1862 loopw - infinite write loop on address range
1863 mtest - simple RAM test
1864 icache - enable or disable instruction cache
1865 dcache - enable or disable data cache
1866 reset - Perform RESET of the CPU
1867 echo - echo args to console
1868 version - print monitor version
1869 help - print online help
1870 ? - alias for 'help'
1873 Monitor Commands - Detailed Description:
1874 ========================================
1878 For now: just type "help <command>".
1881 Note for Redundant Ethernet Interfaces:
1882 =======================================
1884 Some boards come with redundant Ethernet interfaces; U-Boot supports
1885 such configurations and is capable of automatic selection of a
1886 "working" interface when needed. MAC assignment works as follows:
1888 Network interfaces are numbered eth0, eth1, eth2, ... Corresponding
1889 MAC addresses can be stored in the environment as "ethaddr" (=>eth0),
1890 "eth1addr" (=>eth1), "eth2addr", ...
1892 If the network interface stores some valid MAC address (for instance
1893 in SROM), this is used as default address if there is NO correspon-
1894 ding setting in the environment; if the corresponding environment
1895 variable is set, this overrides the settings in the card; that means:
1897 o If the SROM has a valid MAC address, and there is no address in the
1898 environment, the SROM's address is used.
1900 o If there is no valid address in the SROM, and a definition in the
1901 environment exists, then the value from the environment variable is
1904 o If both the SROM and the environment contain a MAC address, and
1905 both addresses are the same, this MAC address is used.
1907 o If both the SROM and the environment contain a MAC address, and the
1908 addresses differ, the value from the environment is used and a
1911 o If neither SROM nor the environment contain a MAC address, an error
1912 is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
1913 a random, locally-assigned MAC is used.
1915 If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresses
1916 will be programmed into hardware as part of the initialization process. This
1917 may be skipped by setting the appropriate 'ethmacskip' environment variable.
1918 The naming convention is as follows:
1919 "ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.
1924 U-Boot is capable of booting (and performing other auxiliary operations on)
1925 images in two formats:
1927 New uImage format (FIT)
1928 -----------------------
1930 Flexible and powerful format based on Flattened Image Tree -- FIT (similar
1931 to Flattened Device Tree). It allows the use of images with multiple
1932 components (several kernels, ramdisks, etc.), with contents protected by
1933 SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.
1939 Old image format is based on binary files which can be basically anything,
1940 preceded by a special header; see the definitions in include/image.h for
1941 details; basically, the header defines the following image properties:
1943 * Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
1944 4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
1945 LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
1946 Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, INTEGRITY).
1947 * Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
1948 IA64, MIPS, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
1949 Currently supported: ARM, Intel x86, MIPS, Nios II, PowerPC).
1950 * Compression Type (uncompressed, gzip, bzip2)
1956 The header is marked by a special Magic Number, and both the header
1957 and the data portions of the image are secured against corruption by
1964 Although U-Boot should support any OS or standalone application
1965 easily, the main focus has always been on Linux during the design of
1968 U-Boot includes many features that so far have been part of some
1969 special "boot loader" code within the Linux kernel. Also, any
1970 "initrd" images to be used are no longer part of one big Linux image;
1971 instead, kernel and "initrd" are separate images. This implementation
1972 serves several purposes:
1974 - the same features can be used for other OS or standalone
1975 applications (for instance: using compressed images to reduce the
1976 Flash memory footprint)
1978 - it becomes much easier to port new Linux kernel versions because
1979 lots of low-level, hardware dependent stuff are done by U-Boot
1981 - the same Linux kernel image can now be used with different "initrd"
1982 images; of course this also means that different kernel images can
1983 be run with the same "initrd". This makes testing easier (you don't
1984 have to build a new "zImage.initrd" Linux image when you just
1985 change a file in your "initrd"). Also, a field-upgrade of the
1986 software is easier now.
1992 Porting Linux to U-Boot based systems:
1993 ---------------------------------------
1995 U-Boot cannot save you from doing all the necessary modifications to
1996 configure the Linux device drivers for use with your target hardware
1997 (no, we don't intend to provide a full virtual machine interface to
2000 But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).
2002 Just make sure your machine specific header file (for instance
2003 include/asm-ppc/tqm8xx.h) includes the same definition of the Board
2004 Information structure as we define in include/asm-<arch>/u-boot.h,
2005 and make sure that your definition of IMAP_ADDR uses the same value
2006 as your U-Boot configuration in CONFIG_SYS_IMMR.
2008 Note that U-Boot now has a driver model, a unified model for drivers.
2009 If you are adding a new driver, plumb it into driver model. If there
2010 is no uclass available, you are encouraged to create one. See
2014 Configuring the Linux kernel:
2015 -----------------------------
2017 No specific requirements for U-Boot. Make sure you have some root
2018 device (initial ramdisk, NFS) for your target system.
2021 Building a Linux Image:
2022 -----------------------
2024 With U-Boot, "normal" build targets like "zImage" or "bzImage" are
2025 not used. If you use recent kernel source, a new build target
2026 "uImage" will exist which automatically builds an image usable by
2027 U-Boot. Most older kernels also have support for a "pImage" target,
2028 which was introduced for our predecessor project PPCBoot and uses a
2029 100% compatible format.
2033 make TQM850L_defconfig
2038 The "uImage" build target uses a special tool (in 'tools/mkimage') to
2039 encapsulate a compressed Linux kernel image with header information,
2040 CRC32 checksum etc. for use with U-Boot. This is what we are doing:
2042 * build a standard "vmlinux" kernel image (in ELF binary format):
2044 * convert the kernel into a raw binary image:
2046 ${CROSS_COMPILE}-objcopy -O binary \
2047 -R .note -R .comment \
2048 -S vmlinux linux.bin
2050 * compress the binary image:
2054 * package compressed binary image for U-Boot:
2056 mkimage -A ppc -O linux -T kernel -C gzip \
2057 -a 0 -e 0 -n "Linux Kernel Image" \
2058 -d linux.bin.gz uImage
2061 The "mkimage" tool can also be used to create ramdisk images for use
2062 with U-Boot, either separated from the Linux kernel image, or
2063 combined into one file. "mkimage" encapsulates the images with a 64
2064 byte header containing information about target architecture,
2065 operating system, image type, compression method, entry points, time
2066 stamp, CRC32 checksums, etc.
2068 "mkimage" can be called in two ways: to verify existing images and
2069 print the header information, or to build new images.
2071 In the first form (with "-l" option) mkimage lists the information
2072 contained in the header of an existing U-Boot image; this includes
2073 checksum verification:
2075 tools/mkimage -l image
2076 -l ==> list image header information
2078 The second form (with "-d" option) is used to build a U-Boot image
2079 from a "data file" which is used as image payload:
2081 tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
2082 -n name -d data_file image
2083 -A ==> set architecture to 'arch'
2084 -O ==> set operating system to 'os'
2085 -T ==> set image type to 'type'
2086 -C ==> set compression type 'comp'
2087 -a ==> set load address to 'addr' (hex)
2088 -e ==> set entry point to 'ep' (hex)
2089 -n ==> set image name to 'name'
2090 -d ==> use image data from 'datafile'
2092 Right now, all Linux kernels for PowerPC systems use the same load
2093 address (0x00000000), but the entry point address depends on the
2096 - 2.2.x kernels have the entry point at 0x0000000C,
2097 - 2.3.x and later kernels have the entry point at 0x00000000.
2099 So a typical call to build a U-Boot image would read:
2101 -> tools/mkimage -n '2.4.4 kernel for TQM850L' \
2102 > -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
2103 > -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
2104 > examples/uImage.TQM850L
2105 Image Name: 2.4.4 kernel for TQM850L
2106 Created: Wed Jul 19 02:34:59 2000
2107 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2108 Data Size: 335725 Bytes = 327.86 kB = 0.32 MB
2109 Load Address: 0x00000000
2110 Entry Point: 0x00000000
2112 To verify the contents of the image (or check for corruption):
2114 -> tools/mkimage -l examples/uImage.TQM850L
2115 Image Name: 2.4.4 kernel for TQM850L
2116 Created: Wed Jul 19 02:34:59 2000
2117 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2118 Data Size: 335725 Bytes = 327.86 kB = 0.32 MB
2119 Load Address: 0x00000000
2120 Entry Point: 0x00000000
2122 NOTE: for embedded systems where boot time is critical you can trade
2123 speed for memory and install an UNCOMPRESSED image instead: this
2124 needs more space in Flash, but boots much faster since it does not
2125 need to be uncompressed:
2127 -> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
2128 -> tools/mkimage -n '2.4.4 kernel for TQM850L' \
2129 > -A ppc -O linux -T kernel -C none -a 0 -e 0 \
2130 > -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
2131 > examples/uImage.TQM850L-uncompressed
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 (uncompressed)
2135 Data Size: 792160 Bytes = 773.59 kB = 0.76 MB
2136 Load Address: 0x00000000
2137 Entry Point: 0x00000000
2140 Similar you can build U-Boot images from a 'ramdisk.image.gz' file
2141 when your kernel is intended to use an initial ramdisk:
2143 -> tools/mkimage -n 'Simple Ramdisk Image' \
2144 > -A ppc -O linux -T ramdisk -C gzip \
2145 > -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
2146 Image Name: Simple Ramdisk Image
2147 Created: Wed Jan 12 14:01:50 2000
2148 Image Type: PowerPC Linux RAMDisk Image (gzip compressed)
2149 Data Size: 566530 Bytes = 553.25 kB = 0.54 MB
2150 Load Address: 0x00000000
2151 Entry Point: 0x00000000
2153 The "dumpimage" tool can be used to disassemble or list the contents of images
2154 built by mkimage. See dumpimage's help output (-h) for details.
2156 Installing a Linux Image:
2157 -------------------------
2159 To downloading a U-Boot image over the serial (console) interface,
2160 you must convert the image to S-Record format:
2162 objcopy -I binary -O srec examples/image examples/image.srec
2164 The 'objcopy' does not understand the information in the U-Boot
2165 image header, so the resulting S-Record file will be relative to
2166 address 0x00000000. To load it to a given address, you need to
2167 specify the target address as 'offset' parameter with the 'loads'
2170 Example: install the image to address 0x40100000 (which on the
2171 TQM8xxL is in the first Flash bank):
2173 => erase 40100000 401FFFFF
2179 ## Ready for S-Record download ...
2180 ~>examples/image.srec
2181 1 2 3 4 5 6 7 8 9 10 11 12 13 ...
2183 15989 15990 15991 15992
2184 [file transfer complete]
2186 ## Start Addr = 0x00000000
2189 You can check the success of the download using the 'iminfo' command;
2190 this includes a checksum verification so you can be sure no data
2191 corruption happened:
2195 ## Checking Image at 40100000 ...
2196 Image Name: 2.2.13 for initrd on TQM850L
2197 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2198 Data Size: 335725 Bytes = 327 kB = 0 MB
2199 Load Address: 00000000
2200 Entry Point: 0000000c
2201 Verifying Checksum ... OK
2207 The "bootm" command is used to boot an application that is stored in
2208 memory (RAM or Flash). In case of a Linux kernel image, the contents
2209 of the "bootargs" environment variable is passed to the kernel as
2210 parameters. You can check and modify this variable using the
2211 "printenv" and "setenv" commands:
2214 => printenv bootargs
2215 bootargs=root=/dev/ram
2217 => setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
2219 => printenv bootargs
2220 bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
2223 ## Booting Linux kernel at 40020000 ...
2224 Image Name: 2.2.13 for NFS on TQM850L
2225 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2226 Data Size: 381681 Bytes = 372 kB = 0 MB
2227 Load Address: 00000000
2228 Entry Point: 0000000c
2229 Verifying Checksum ... OK
2230 Uncompressing Kernel Image ... OK
2231 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
2232 Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
2233 time_init: decrementer frequency = 187500000/60
2234 Calibrating delay loop... 49.77 BogoMIPS
2235 Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
2238 If you want to boot a Linux kernel with initial RAM disk, you pass
2239 the memory addresses of both the kernel and the initrd image (PPBCOOT
2240 format!) to the "bootm" command:
2242 => imi 40100000 40200000
2244 ## Checking Image at 40100000 ...
2245 Image Name: 2.2.13 for initrd on TQM850L
2246 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2247 Data Size: 335725 Bytes = 327 kB = 0 MB
2248 Load Address: 00000000
2249 Entry Point: 0000000c
2250 Verifying Checksum ... OK
2252 ## Checking Image at 40200000 ...
2253 Image Name: Simple Ramdisk Image
2254 Image Type: PowerPC Linux RAMDisk Image (gzip compressed)
2255 Data Size: 566530 Bytes = 553 kB = 0 MB
2256 Load Address: 00000000
2257 Entry Point: 00000000
2258 Verifying Checksum ... OK
2260 => bootm 40100000 40200000
2261 ## Booting Linux kernel at 40100000 ...
2262 Image Name: 2.2.13 for initrd on TQM850L
2263 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2264 Data Size: 335725 Bytes = 327 kB = 0 MB
2265 Load Address: 00000000
2266 Entry Point: 0000000c
2267 Verifying Checksum ... OK
2268 Uncompressing Kernel Image ... OK
2269 ## Loading RAMDisk Image at 40200000 ...
2270 Image Name: Simple Ramdisk Image
2271 Image Type: PowerPC Linux RAMDisk Image (gzip compressed)
2272 Data Size: 566530 Bytes = 553 kB = 0 MB
2273 Load Address: 00000000
2274 Entry Point: 00000000
2275 Verifying Checksum ... OK
2276 Loading Ramdisk ... OK
2277 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
2278 Boot arguments: root=/dev/ram
2279 time_init: decrementer frequency = 187500000/60
2280 Calibrating delay loop... 49.77 BogoMIPS
2282 RAMDISK: Compressed image found at block 0
2283 VFS: Mounted root (ext2 filesystem).
2287 Boot Linux and pass a flat device tree:
2290 First, U-Boot must be compiled with the appropriate defines. See the section
2291 titled "Linux Kernel Interface" above for a more in depth explanation. The
2292 following is an example of how to start a kernel and pass an updated
2298 oft=oftrees/mpc8540ads.dtb
2299 => tftp $oftaddr $oft
2300 Speed: 1000, full duplex
2302 TFTP from server 192.168.1.1; our IP address is 192.168.1.101
2303 Filename 'oftrees/mpc8540ads.dtb'.
2304 Load address: 0x300000
2307 Bytes transferred = 4106 (100a hex)
2308 => tftp $loadaddr $bootfile
2309 Speed: 1000, full duplex
2311 TFTP from server 192.168.1.1; our IP address is 192.168.1.2
2313 Load address: 0x200000
2314 Loading:############
2316 Bytes transferred = 1029407 (fb51f hex)
2321 => bootm $loadaddr - $oftaddr
2322 ## Booting image at 00200000 ...
2323 Image Name: Linux-2.6.17-dirty
2324 Image Type: PowerPC Linux Kernel Image (gzip compressed)
2325 Data Size: 1029343 Bytes = 1005.2 kB
2326 Load Address: 00000000
2327 Entry Point: 00000000
2328 Verifying Checksum ... OK
2329 Uncompressing Kernel Image ... OK
2330 Booting using flat device tree at 0x300000
2331 Using MPC85xx ADS machine description
2332 Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
2336 More About U-Boot Image Types:
2337 ------------------------------
2339 U-Boot supports the following image types:
2341 "Standalone Programs" are directly runnable in the environment
2342 provided by U-Boot; it is expected that (if they behave
2343 well) you can continue to work in U-Boot after return from
2344 the Standalone Program.
2345 "OS Kernel Images" are usually images of some Embedded OS which
2346 will take over control completely. Usually these programs
2347 will install their own set of exception handlers, device
2348 drivers, set up the MMU, etc. - this means, that you cannot
2349 expect to re-enter U-Boot except by resetting the CPU.
2350 "RAMDisk Images" are more or less just data blocks, and their
2351 parameters (address, size) are passed to an OS kernel that is
2353 "Multi-File Images" contain several images, typically an OS
2354 (Linux) kernel image and one or more data images like
2355 RAMDisks. This construct is useful for instance when you want
2356 to boot over the network using BOOTP etc., where the boot
2357 server provides just a single image file, but you want to get
2358 for instance an OS kernel and a RAMDisk image.
2360 "Multi-File Images" start with a list of image sizes, each
2361 image size (in bytes) specified by an "uint32_t" in network
2362 byte order. This list is terminated by an "(uint32_t)0".
2363 Immediately after the terminating 0 follow the images, one by
2364 one, all aligned on "uint32_t" boundaries (size rounded up to
2365 a multiple of 4 bytes).
2367 "Firmware Images" are binary images containing firmware (like
2368 U-Boot or FPGA images) which usually will be programmed to
2371 "Script files" are command sequences that will be executed by
2372 U-Boot's command interpreter; this feature is especially
2373 useful when you configure U-Boot to use a real shell (hush)
2374 as command interpreter.
2376 Booting the Linux zImage:
2377 -------------------------
2379 On some platforms, it's possible to boot Linux zImage. This is done
2380 using the "bootz" command. The syntax of "bootz" command is the same
2381 as the syntax of "bootm" command.
2383 Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply
2384 kernel with raw initrd images. The syntax is slightly different, the
2385 address of the initrd must be augmented by it's size, in the following
2386 format: "<initrd addres>:<initrd size>".
2392 One of the features of U-Boot is that you can dynamically load and
2393 run "standalone" applications, which can use some resources of
2394 U-Boot like console I/O functions or interrupt services.
2396 Two simple examples are included with the sources:
2401 'examples/hello_world.c' contains a small "Hello World" Demo
2402 application; it is automatically compiled when you build U-Boot.
2403 It's configured to run at address 0x00040004, so you can play with it
2407 ## Ready for S-Record download ...
2408 ~>examples/hello_world.srec
2409 1 2 3 4 5 6 7 8 9 10 11 ...
2410 [file transfer complete]
2412 ## Start Addr = 0x00040004
2414 => go 40004 Hello World! This is a test.
2415 ## Starting application at 0x00040004 ...
2426 Hit any key to exit ...
2428 ## Application terminated, rc = 0x0
2430 Another example, which demonstrates how to register a CPM interrupt
2431 handler with the U-Boot code, can be found in 'examples/timer.c'.
2432 Here, a CPM timer is set up to generate an interrupt every second.
2433 The interrupt service routine is trivial, just printing a '.'
2434 character, but this is just a demo program. The application can be
2435 controlled by the following keys:
2437 ? - print current values og the CPM Timer registers
2438 b - enable interrupts and start timer
2439 e - stop timer and disable interrupts
2440 q - quit application
2443 ## Ready for S-Record download ...
2444 ~>examples/timer.srec
2445 1 2 3 4 5 6 7 8 9 10 11 ...
2446 [file transfer complete]
2448 ## Start Addr = 0x00040004
2451 ## Starting application at 0x00040004 ...
2454 tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
2457 [q, b, e, ?] Set interval 1000000 us
2460 [q, b, e, ?] ........
2461 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
2464 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
2467 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
2470 tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
2472 [q, b, e, ?] ...Stopping timer
2474 [q, b, e, ?] ## Application terminated, rc = 0x0
2480 Over time, many people have reported problems when trying to use the
2481 "minicom" terminal emulation program for serial download. I (wd)
2482 consider minicom to be broken, and recommend not to use it. Under
2483 Unix, I recommend to use C-Kermit for general purpose use (and
2484 especially for kermit binary protocol download ("loadb" command), and
2485 use "cu" for S-Record download ("loads" command). See
2486 https://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.
2487 for help with kermit.
2490 Nevertheless, if you absolutely want to use it try adding this
2491 configuration to your "File transfer protocols" section:
2493 Name Program Name U/D FullScr IO-Red. Multi
2494 X kermit /usr/bin/kermit -i -l %l -s Y U Y N N
2495 Y kermit /usr/bin/kermit -i -l %l -r N D Y N N
2498 Implementation Internals:
2499 =========================
2501 The following is not intended to be a complete description of every
2502 implementation detail. However, it should help to understand the
2503 inner workings of U-Boot and make it easier to port it to custom
2507 Initial Stack, Global Data:
2508 ---------------------------
2510 The implementation of U-Boot is complicated by the fact that U-Boot
2511 starts running out of ROM (flash memory), usually without access to
2512 system RAM (because the memory controller is not initialized yet).
2513 This means that we don't have writable Data or BSS segments, and BSS
2514 is not initialized as zero. To be able to get a C environment working
2515 at all, we have to allocate at least a minimal stack. Implementation
2516 options for this are defined and restricted by the CPU used: Some CPU
2517 models provide on-chip memory (like the IMMR area on MPC8xx and
2518 MPC826x processors), on others (parts of) the data cache can be
2519 locked as (mis-) used as memory, etc.
2521 Chris Hallinan posted a good summary of these issues to the
2522 U-Boot mailing list:
2524 Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
2525 From: "Chris Hallinan" <clh@net1plus.com>
2526 Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
2529 Correct me if I'm wrong, folks, but the way I understand it
2530 is this: Using DCACHE as initial RAM for Stack, etc, does not
2531 require any physical RAM backing up the cache. The cleverness
2532 is that the cache is being used as a temporary supply of
2533 necessary storage before the SDRAM controller is setup. It's
2534 beyond the scope of this list to explain the details, but you
2535 can see how this works by studying the cache architecture and
2536 operation in the architecture and processor-specific manuals.
2538 OCM is On Chip Memory, which I believe the 405GP has 4K. It
2539 is another option for the system designer to use as an
2540 initial stack/RAM area prior to SDRAM being available. Either
2541 option should work for you. Using CS 4 should be fine if your
2542 board designers haven't used it for something that would
2543 cause you grief during the initial boot! It is frequently not
2546 CFG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
2547 with your processor/board/system design. The default value
2548 you will find in any recent u-boot distribution in
2549 walnut.h should work for you. I'd set it to a value larger
2550 than your SDRAM module. If you have a 64MB SDRAM module, set
2551 it above 400_0000. Just make sure your board has no resources
2552 that are supposed to respond to that address! That code in
2553 start.S has been around a while and should work as is when
2554 you get the config right.
2559 It is essential to remember this, since it has some impact on the C
2560 code for the initialization procedures:
2562 * Initialized global data (data segment) is read-only. Do not attempt
2565 * Do not use any uninitialized global data (or implicitly initialized
2566 as zero data - BSS segment) at all - this is undefined, initiali-
2567 zation is performed later (when relocating to RAM).
2569 * Stack space is very limited. Avoid big data buffers or things like
2572 Having only the stack as writable memory limits means we cannot use
2573 normal global data to share information between the code. But it
2574 turned out that the implementation of U-Boot can be greatly
2575 simplified by making a global data structure (gd_t) available to all
2576 functions. We could pass a pointer to this data as argument to _all_
2577 functions, but this would bloat the code. Instead we use a feature of
2578 the GCC compiler (Global Register Variables) to share the data: we
2579 place a pointer (gd) to the global data into a register which we
2580 reserve for this purpose.
2582 When choosing a register for such a purpose we are restricted by the
2583 relevant (E)ABI specifications for the current architecture, and by
2584 GCC's implementation.
2586 For PowerPC, the following registers have specific use:
2588 R2: reserved for system use
2589 R3-R4: parameter passing and return values
2590 R5-R10: parameter passing
2591 R13: small data area pointer
2595 (U-Boot also uses R12 as internal GOT pointer. r12
2596 is a volatile register so r12 needs to be reset when
2597 going back and forth between asm and C)
2599 ==> U-Boot will use R2 to hold a pointer to the global data
2601 Note: on PPC, we could use a static initializer (since the
2602 address of the global data structure is known at compile time),
2603 but it turned out that reserving a register results in somewhat
2604 smaller code - although the code savings are not that big (on
2605 average for all boards 752 bytes for the whole U-Boot image,
2606 624 text + 127 data).
2608 On ARM, the following registers are used:
2610 R0: function argument word/integer result
2611 R1-R3: function argument word
2612 R9: platform specific
2613 R10: stack limit (used only if stack checking is enabled)
2614 R11: argument (frame) pointer
2615 R12: temporary workspace
2618 R15: program counter
2620 ==> U-Boot will use R9 to hold a pointer to the global data
2622 Note: on ARM, only R_ARM_RELATIVE relocations are supported.
2624 On Nios II, the ABI is documented here:
2625 https://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
2627 ==> U-Boot will use gp to hold a pointer to the global data
2629 Note: on Nios II, we give "-G0" option to gcc and don't use gp
2630 to access small data sections, so gp is free.
2632 On RISC-V, the following registers are used:
2634 x0: hard-wired zero (zero)
2635 x1: return address (ra)
2636 x2: stack pointer (sp)
2637 x3: global pointer (gp)
2638 x4: thread pointer (tp)
2639 x5: link register (t0)
2640 x8: frame pointer (fp)
2641 x10-x11: arguments/return values (a0-1)
2642 x12-x17: arguments (a2-7)
2643 x28-31: temporaries (t3-6)
2644 pc: program counter (pc)
2646 ==> U-Boot will use gp to hold a pointer to the global data
2651 U-Boot runs in system state and uses physical addresses, i.e. the
2652 MMU is not used either for address mapping nor for memory protection.
2654 The available memory is mapped to fixed addresses using the memory
2655 controller. In this process, a contiguous block is formed for each
2656 memory type (Flash, SDRAM, SRAM), even when it consists of several
2657 physical memory banks.
2659 U-Boot is installed in the first 128 kB of the first Flash bank (on
2660 TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
2661 booting and sizing and initializing DRAM, the code relocates itself
2662 to the upper end of DRAM. Immediately below the U-Boot code some
2663 memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
2664 configuration setting]. Below that, a structure with global Board
2665 Info data is placed, followed by the stack (growing downward).
2667 Additionally, some exception handler code is copied to the low 8 kB
2668 of DRAM (0x00000000 ... 0x00001FFF).
2670 So a typical memory configuration with 16 MB of DRAM could look like
2673 0x0000 0000 Exception Vector code
2676 0x0000 2000 Free for Application Use
2682 0x00FB FF20 Monitor Stack (Growing downward)
2683 0x00FB FFAC Board Info Data and permanent copy of global data
2684 0x00FC 0000 Malloc Arena
2687 0x00FE 0000 RAM Copy of Monitor Code
2688 ... eventually: LCD or video framebuffer
2689 ... eventually: pRAM (Protected RAM - unchanged by reset)
2690 0x00FF FFFF [End of RAM]
2693 System Initialization:
2694 ----------------------
2696 In the reset configuration, U-Boot starts at the reset entry point
2697 (on most PowerPC systems at address 0x00000100). Because of the reset
2698 configuration for CS0# this is a mirror of the on board Flash memory.
2699 To be able to re-map memory U-Boot then jumps to its link address.
2700 To be able to implement the initialization code in C, a (small!)
2701 initial stack is set up in the internal Dual Ported RAM (in case CPUs
2702 which provide such a feature like), or in a locked part of the data
2703 cache. After that, U-Boot initializes the CPU core, the caches and
2706 Next, all (potentially) available memory banks are mapped using a
2707 preliminary mapping. For example, we put them on 512 MB boundaries
2708 (multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
2709 on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
2710 programmed for SDRAM access. Using the temporary configuration, a
2711 simple memory test is run that determines the size of the SDRAM
2714 When there is more than one SDRAM bank, and the banks are of
2715 different size, the largest is mapped first. For equal size, the first
2716 bank (CS2#) is mapped first. The first mapping is always for address
2717 0x00000000, with any additional banks following immediately to create
2718 contiguous memory starting from 0.
2720 Then, the monitor installs itself at the upper end of the SDRAM area
2721 and allocates memory for use by malloc() and for the global Board
2722 Info data; also, the exception vector code is copied to the low RAM
2723 pages, and the final stack is set up.
2725 Only after this relocation will you have a "normal" C environment;
2726 until that you are restricted in several ways, mostly because you are
2727 running from ROM, and because the code will have to be relocated to a
2731 U-Boot Porting Guide:
2732 ----------------------
2734 [Based on messages by Jerry Van Baren in the U-Boot-Users mailing
2738 int main(int argc, char *argv[])
2740 sighandler_t no_more_time;
2742 signal(SIGALRM, no_more_time);
2743 alarm(PROJECT_DEADLINE - toSec (3 * WEEK));
2745 if (available_money > available_manpower) {
2746 Pay consultant to port U-Boot;
2750 Download latest U-Boot source;
2752 Subscribe to u-boot mailing list;
2755 email("Hi, I am new to U-Boot, how do I get started?");
2758 Read the README file in the top level directory;
2759 Read https://www.denx.de/wiki/bin/view/DULG/Manual;
2760 Read applicable doc/README.*;
2761 Read the source, Luke;
2762 /* find . -name "*.[chS]" | xargs grep -i <keyword> */
2765 if (available_money > toLocalCurrency ($2500))
2768 Add a lot of aggravation and time;
2770 if (a similar board exists) { /* hopefully... */
2771 cp -a board/<similar> board/<myboard>
2772 cp include/configs/<similar>.h include/configs/<myboard>.h
2774 Create your own board support subdirectory;
2775 Create your own board include/configs/<myboard>.h file;
2777 Edit new board/<myboard> files
2778 Edit new include/configs/<myboard>.h
2783 Add / modify source code;
2787 email("Hi, I am having problems...");
2789 Send patch file to the U-Boot email list;
2790 if (reasonable critiques)
2791 Incorporate improvements from email list code review;
2793 Defend code as written;
2799 void no_more_time (int sig)
2808 The U-Boot projects depends on contributions from the user community.
2809 If you want to participate, please, have a look at the 'General'
2810 section of https://u-boot.readthedocs.io/en/latest/develop/index.html
2811 where we describe coding standards and the patch submission process.