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Using QEMU for Embedded Systems Development, Part 3


By Manoj Kumar on August 1, 2011 in Coding, Developers · 4 Comments


It's time to u-boot

This is the last article of this series on QEMU. In the previous article, we worked on bare-metal programming, and discussed the need for a bootloader. Most GNU/Linux distros use GRUB as their boot-loader (earlier, LILO was the choice). In this article, we will test the famous U-Boot (Universal BootLoader).


In embedded systems, especially in mobile devices, ARM processor-based devices are leading the market. For ARM, U-Boot is the best choice for a bootloader. The good thing about it is that we can use it for different architectures like PPC, MIPS, x86, etc. So let’s get started.

Download and compile U-Boot


U-Boot is released under a GPL licence. Download it from this FTP server, which has every version of U-Boot available. For this article, I got version 1.2.0 (u-boot-1.2.0.tar.bz2). Extract the downloaded tar ball and enter the source code directory:


# tar -jxvf u-boot-1.2.0.tar.bz2

# cd u-boot-1.2.0


To begin, we must configure U-Boot for a particular board. We will use the same ARM Versatile Platform Baseboard (versatilepb) we used in the previous article, so let’s run:


# make versatilepb_config arch=ARM CROSS_COMPILE=arm-none-eabi-

Configuring for versatile board...

Variant:: PB926EJ-S


After configuration is done, compile the source code:


# make all arch=ARM CROSS_COMPILE=arm-none-eabi-

for dir in tools examples post post/cpu ; do make -C $dir _depend ; done

make[1]: Entering directory `/root/qemu/u-boot-1.2.0/tools'

ln -s ../common/environment.c environment.c

.

.

G++_Lite/bin/../lib/gcc/arm-none-eabi/4.4.1 -lgcc \

            -Map u-boot.map -o u-boot

arm-none-eabi-objcopy --gap-fill=0xff -O srec u-boot u-boot.srec

arm-none-eabi-objcopy --gap-fill=0xff -O binary u-boot u-boot.bin


Find the size of the compiled U-Boot binary file (around 72 KB in my experience) with ls -lh u-boot* — we will use it later in this article. I assume that you have set up QEMU, networking and the ARM tool chain, as explained in previous articles in this series (1, 2, 3). If not, then I suggest you read the last three articles.

Boot U-Boot in QEMU


Now we can boot the U-Boot binary in QEMU, which is simple. Instead of specifying the Linux kernel as the file to boot in QEMU, use the U-Boot binary:


# qemu-system-arm -M versatilepb -nographic -kernel u-boot.bin


Run some commands in U-Boot, to check if it is working:


Versatile # printenv

bootargs=root=/dev/nfs mem=128M ip=dhcp netdev=25,0,0xf1010000,0xf1010010,eth0

bootdelay=2

baudrate=38400

bootfile="/tftpboot/uImage"

stdin=serial

stdout=serial

stderr=serial

verify=n

Environment size: 184/65532 bytes


U-Boot


Figure 1: U-Boot


The next step is to boot a small program from U-Boot. In the previous article, we wrote a small bare-metal program — so let us use that.


We will create a flash binary image that includes u-boot.bin and the bare-metal program in it. The test program from the last article will be used here again with some modification. As the u-boot.bin size is around 72 KB, we will move our sample program upward in memory. In the linker script, change the starting address of the program:


ENTRY(_Start)

SECTIONS

{

. = 0x100000;

startup : { startup.o(.text)}

.data : {*(.data)}

.bss : {*(.bss)}

. = . + 0x500;

sp_top = .;

}


Compile the test program as shown below:


# arm-none-eabi-gcc -c -mcpu=arm926ej-s init.c -o init.o

# arm-none-eabi-as -mcpu=arm926ej-s startup.s -o startup.o

# arm-none-eabi-ld -T linker.ld init.o startup.o -o test.elf

# arm-none-eabi-objcopy -O binary test.elf test.bin


Now, our test program’s binary file and the u-boot.bin must be packed in a single file. Let’s use the mkimage tool for this; locate it in the U-Boot source-code directory.


# mkimage -A arm -C none -O linux -T kernel -d test.bin -a 0x00100000 -e 0x00100000 test.uimg

Image Name:

Created:      Wed Jul 6 13:29:54 2011

Image Type:   ARM Linux Kernel Image (uncompressed)

Data Size:    148 Bytes = 0.14 kB = 0.00 MB

Load Address: 0x00100000

Entry Point:  0x00100000


Our sample binary file is ready. Let’s combine it with u-boot.bin to create the final flash image file:


#cat u-boot.bin test.uimg > flash.bin


Calculate the starting address of the test program in the flash.bin file:


# printf "0x%X" $(expr $(stat -c%s u-boot.bin) + 65536)

0x21C68


Boot the flash image in QEMU:


# qemu-system-arm -M versatilepb -nographic -kernel flash.bin


Now verify the image address in U-Boot:


Versatile # iminfo 0x21C68

## Checking Image at 00021c68 ...

Image Name:

Image Type:   ARM Linux Kernel Image (uncompressed)

Data Size:    136 Bytes =  0.1 kB

Load Address: 00100000

Entry Point:  00100000

Verifying Checksum ... OK


The image is present at the address 0x21C68. Boot it by executing the bootm command:


Versatile # bootm 0x21C68

## Booting image at 00021c68 ...

Image Name:

Image Type:   ARM Linux Kernel Image (uncompressed)

Data Size:    148 Bytes =  0.1 kB

Load Address: 00100000

Entry Point:  00100000

OK


Starting kernel ...


Hello Open World


That’s all folks!

Acknowledgement


This article is inspired by the following blog post: “U-boot for ARM on QEMU“.




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