1 .. SPDX-License-Identifier: GPL-2.0+
2 .. sectionauthor:: Bin Meng <bmeng.cn@gmail.com>
7 Build instructions for bare mode
8 --------------------------------
10 To build u-boot.rom for QEMU x86 targets, just simply run::
12 $ make qemu-x86_defconfig (for 32-bit)
13 $ make qemu-x86_64_defconfig (for 64-bit)
16 Note this default configuration will build a U-Boot for the QEMU x86 i440FX
17 board. To build a U-Boot against QEMU x86 Q35 board, you can change the build
18 configuration during the 'make menuconfig' process like below::
20 Device Tree Control --->
22 (qemu-x86_q35) Default Device Tree for DT control
24 Test with QEMU for bare mode
25 ----------------------------
27 QEMU is a fancy emulator that can enable us to test U-Boot without access to
28 a real x86 board. Please make sure your QEMU version is 2.3.0 or above test
29 U-Boot. To launch QEMU with u-boot.rom, call QEMU as follows::
31 $ qemu-system-i386 -nographic -bios path/to/u-boot.rom
33 This will instantiate an emulated x86 board with i440FX and PIIX chipset. QEMU
34 also supports emulating an x86 board with Q35 and ICH9 based chipset, which is
35 also supported by U-Boot. To instantiate such a machine, call QEMU with::
37 $ qemu-system-i386 -nographic -bios path/to/u-boot.rom -M q35
39 Note by default QEMU instantiated boards only have 128 MiB system memory. But
40 it is enough to have U-Boot boot and function correctly. You can increase the
41 system memory by pass '-m' parameter to QEMU if you want more memory::
43 $ qemu-system-i386 -nographic -bios path/to/u-boot.rom -m 1024
45 This creates a board with 1 GiB system memory. Currently U-Boot for QEMU only
46 supports 3 GiB maximum system memory and reserves the last 1 GiB address space
47 for PCI device memory-mapped I/O and other stuff, so the maximum value of '-m'
50 QEMU emulates a graphic card which U-Boot supports. Removing '-nographic' will
51 show QEMU's VGA console window. Note this will disable QEMU's serial output.
52 If you want to check both consoles, use '-serial stdio'.
54 Multicore is also supported by QEMU via '-smp n' where n is the number of cores
55 to instantiate. Note, the maximum supported CPU number in QEMU is 255.
57 The fw_cfg interface in QEMU also provides information about kernel data,
58 initrd, command-line arguments and more. U-Boot supports directly accessing
59 these informtion from fw_cfg interface, which saves the time of loading them
60 from hard disk or network again, through emulated devices. To use it , simply
61 providing them in QEMU command line::
63 $ qemu-system-i386 -nographic -bios path/to/u-boot.rom -m 1024 \
64 -kernel /path/to/bzImage -append 'root=/dev/ram console=ttyS0' \
65 -initrd /path/to/initrd -smp 8
67 Note: -initrd and -smp are both optional
69 Then start QEMU, in U-Boot command line use the following U-Boot command to
73 qfw - QEMU firmware interface
77 - list : print firmware(s) currently loaded
78 - cpus : print online cpu number
79 - load <kernel addr> <initrd addr> : load kernel and initrd (if any) and setup for zboot
82 loading kernel to address 01000000 size 5d9d30 initrd 04000000 size 1b1ab50
84 Here the kernel (bzImage) is loaded to 01000000 and initrd is to 04000000. Then,
85 'zboot' can be used to boot the kernel::
87 => zboot 01000000 - 04000000 1b1ab50
89 To run 64-bit U-Boot, qemu-system-x86_64 should be used instead, e.g.::
91 $ qemu-system-x86_64 -nographic -bios path/to/u-boot.rom
93 A specific CPU can be specified via the '-cpu' parameter but please make
94 sure the specified CPU supports 64-bit like '-cpu core2duo'. Conversely
95 '-cpu pentium' won't work for obvious reasons that the processor only
98 Note 64-bit support is very preliminary at this point. Lots of features
99 are missing in the 64-bit world. One notable feature is the VGA console
100 support which is currently missing, so that you must specify '-nographic'
101 to get 64-bit U-Boot up and running.