Using QEMU for Embedded Systems Development, Part 3

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 theprevious 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) withls -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

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 theu-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 themkimage 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 thebootm 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!