119 lines
4.7 KiB
ReStructuredText
119 lines
4.7 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Bin Meng <bmeng.cn@gmail.com>
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QEMU x86
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========
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Build instructions for bare mode
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--------------------------------
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To build u-boot.rom for QEMU x86 targets, just simply run::
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$ make qemu-x86_defconfig (for 32-bit)
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$ make qemu-x86_64_defconfig (for 64-bit)
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$ make all
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Note this default configuration will build a U-Boot for the QEMU x86 i440FX
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board. To build a U-Boot against QEMU x86 Q35 board, you can change the build
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configuration during the 'make menuconfig' process like below::
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Device Tree Control --->
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...
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(qemu-x86_q35) Default Device Tree for DT control
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Test with QEMU for bare mode
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----------------------------
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QEMU is a fancy emulator that can enable us to test U-Boot without access to
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a real x86 board. Please make sure your QEMU version is 2.3.0 or above test
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U-Boot. To launch QEMU with u-boot.rom, call QEMU as follows::
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$ qemu-system-i386 -nographic -bios path/to/u-boot.rom
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This will instantiate an emulated x86 board with i440FX and PIIX chipset. QEMU
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also supports emulating an x86 board with Q35 and ICH9 based chipset, which is
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also supported by U-Boot. To instantiate such a machine, call QEMU with::
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$ qemu-system-i386 -nographic -bios path/to/u-boot.rom -M q35
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Note by default QEMU instantiated boards only have 128 MiB system memory. But
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it is enough to have U-Boot boot and function correctly. You can increase the
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system memory by pass '-m' parameter to QEMU if you want more memory::
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$ qemu-system-i386 -nographic -bios path/to/u-boot.rom -m 1024
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This creates a board with 1 GiB system memory. Currently U-Boot for QEMU only
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supports 3 GiB maximum system memory and reserves the last 1 GiB address space
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for PCI device memory-mapped I/O and other stuff, so the maximum value of '-m'
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would be 3072.
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QEMU emulates a graphic card which U-Boot supports. Removing '-nographic' will
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show QEMU's VGA console window. Note this will disable QEMU's serial output.
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If you want to check both consoles, use '-serial stdio'.
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Multicore is also supported by QEMU via '-smp n' where n is the number of cores
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to instantiate. Note, the maximum supported CPU number in QEMU is 255.
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U-Boot uses 'distro_bootcmd' by default when booting on x86 QEMU. This tries to
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load a boot script, kernel, and ramdisk from several different interfaces. For
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the default boot order, see 'qemu-x86.h'. For more information, see
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'README.distro'. Most Linux distros can be booted by writing a uboot script.
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For example, Debian (stretch) can be booted by creating a script file named
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'boot.txt' with the contents::
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setenv bootargs root=/dev/sda1 ro
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load ${devtype} ${devnum}:${distro_bootpart} ${kernel_addr_r} /vmlinuz
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load ${devtype} ${devnum}:${distro_bootpart} ${ramdisk_addr_r} /initrd.img
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zboot ${kernel_addr_r} - ${ramdisk_addr_r} ${filesize}
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Then compile and install it with::
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$ apt install u-boot-tools && \
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mkimage -T script -C none -n "Boot script" -d boot.txt /boot/boot.scr
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The fw_cfg interface in QEMU also provides information about kernel data,
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initrd, command-line arguments and more. U-Boot supports directly accessing
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these informtion from fw_cfg interface, which saves the time of loading them
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from hard disk or network again, through emulated devices. To use it , simply
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providing them in QEMU command line::
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$ qemu-system-i386 -nographic -bios path/to/u-boot.rom -m 1024 \
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-kernel /path/to/bzImage -append 'root=/dev/ram console=ttyS0' \
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-initrd /path/to/initrd -smp 8
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Note: -initrd and -smp are both optional
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Then start QEMU, in U-Boot command line use the following U-Boot command to
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setup kernel::
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=> qfw
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qfw - QEMU firmware interface
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Usage:
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qfw <command>
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- list : print firmware(s) currently loaded
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- cpus : print online cpu number
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- load <kernel addr> <initrd addr> : load kernel and initrd (if any) and setup for zboot
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=> qfw load
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loading kernel to address 01000000 size 5d9d30 initrd 04000000 size 1b1ab50
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Here the kernel (bzImage) is loaded to 01000000 and initrd is to 04000000. Then,
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'zboot' can be used to boot the kernel::
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=> zboot 01000000 - 04000000 1b1ab50
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To run 64-bit U-Boot, qemu-system-x86_64 should be used instead, e.g.::
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$ qemu-system-x86_64 -nographic -bios path/to/u-boot.rom
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A specific CPU can be specified via the '-cpu' parameter but please make
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sure the specified CPU supports 64-bit like '-cpu core2duo'. Conversely
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'-cpu pentium' won't work for obvious reasons that the processor only
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supports 32-bit.
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Note 64-bit support is very preliminary at this point. Lots of features
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are missing in the 64-bit world. One notable feature is the VGA console
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support which is currently missing, so that you must specify '-nographic'
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to get 64-bit U-Boot up and running.
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