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[QEMU] Build u-boot for ARM.md

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[QEMU] Build u-boot for ARM.md

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In the previous post, we have the toolchain arm-unknown-linux-gnueabi in hand. In this tutorial, it will be used to build a u-boot and run it using QEMU.

Get the u-boot repository

	git clone https://source.denx.de/u-boot/u-boot.git`
	cd u-boot

To make use of the toolchain, you need to add the directory to your path using the following command:

	PATH=~/x-tools/arm-unknown-linux-gnueabi/bin:$PATH

Build u-boot

You need to inform U-Boot of the prefix for your cross compiler by setting the make variable CROSS_COMPILE and then select the configuration file using a command make [board]_defconfig. Here I use QEMU to run the u-boot so I use qemu_arm_defconfig board configuration.

	/* Clean everything before making the config for the new board*/
	make clean
	make mrproper
	make distclean

	make CROSS_COMPILE=arm-unknown-linux-gnueabi- ARCH=arm qemu_arm_defconfig

Note: There are a lot of board_xxx_deconfig files in <PATH>/u-boot/configs. You can take a look to find what is the board target that you need.

Then you can make change of the configuration file by using:

	make CROSS_COMPILE=arm-unknown-linux-gnueabi- ARCH=arm menuconfig

I will keep it as default in this example.

Then you can build the u-boot for your target board

	make CROSS_COMPILE=arm-unknown-linux-gnueabi- ARCH=arm

After done, it will give you some different u-boot files for different purposes:

- u-boot : This is U-Boot in ELF object format, suitable for use with a debugger
- u-boot.map : This is the symbol table
- u-boot.bin : This is U-Boot in raw binary format, suitable for running on
- u-boot.img : This is u-boot.bin with a U-Boot header added, suitable for
- u-boot.srec : This is U-Boot in Motorola srec format, suitable for your device uploading to a running copy of U-Boot transferring over a serial connection

Run the u-boot with QEMU

	qemu-system-arm -machine virt -nographic -bios u-boot.bin

Note: The guide for running u-boot can be found at <PATH>/u-boot/doc/board/emulation

You should get the console output of the u-boot as below:

U-Boot 2022.04-rc3 (Mar 04 2022 - 22:20:37 +0700)

DRAM:  128 MiB
Core:  42 devices, 11 uclasses, devicetree: board
Flash: 64 MiB
Loading Environment from Flash... *** Warning - bad CRC, using default environment

In:    pl011@9000000
Out:   pl011@9000000
Err:   pl011@9000000
Net:   eth0: virtio-net#32
Hit any key to stop autoboot:  0 
starting USB...
No working controllers found
USB is stopped. Please issue 'usb start' first.
scanning bus for devices...

Device 0: unknown device

Device 0: unknown device
starting USB...
No working controllers found
BOOTP broadcast 1
DHCP client bound to address 10.0.2.15 (2 ms)
Using virtio-net#32 device
TFTP from server 10.0.2.2; our IP address is 10.0.2.15
Filename 'boot.scr.uimg'.
Load address: 0x40200000
Loading: *
TFTP error: 'Access violation' (2)
Not retrying...
BOOTP broadcast 1
DHCP client bound to address 10.0.2.15 (0 ms)
Using virtio-net#32 device
TFTP from server 10.0.2.2; our IP address is 10.0.2.15
Filename 'boot.scr.uimg'.
Load address: 0x40400000
Loading: *
TFTP error: 'Access violation' (2)
Not retrying...
=>

You can check your cross compiler by check version in the u-boot. Or help to see all u-boot supported commands.

=> version
U-Boot 2022.04-rc3 (Mar 04 2022 - 22:20:37 +0700)

arm-unknown-linux-gnueabi-gcc (crosstool-NG 1.24.0.551_1e47ca1) 11.2.0
GNU ld (crosstool-NG 1.24.0.551_1e47ca1) 2.38

At this point, you already have the u-boot in the board target and ready to boot the kernel. Note: This steps seem to be easy since using the QEMU, it may require more knowleges to load a u-boot to the real board.