Bare metal

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Here is an example of how to run your own C code on the bare metal, without any operating system. Since I don't yet have a physical device, this has only been tested using Qemu.

Example program

The example program does nothing but blink the LCD backlight on and off. A simple first exercise might be to change it to blink out "hello world" in morse code.

C code (app.c)

#define GPBDAT *((volatile unsigned long*)0x56000014)

void cstart(void)
{
	int i;
	while (1) {
		GPBDAT ^= 1; /* toggle the backlight */
		for (i = 0; i < 50000000; i++); /* delay a little bit */
	}
}

Assembler head (app.S)

.text
.globl _start
_start:
	mov	sp, #0x30000000    @ start of RAM
	add	sp, sp, #0xa00000  @ 10mb in, should be a safe place to put our stack
	b	cstart             @ call C code

Linker script (app.lds)

SECTIONS
{
  . = 0x35000000;
}

Makefile

Change the CROSS variable to point at the location of your cross-compiler. The example assumes a build environment was setup with the MokoMakefile in /mnt/oe/openmoko.

CROSS=/mnt/oe/openmoko/build/tmp/cross/arm-angstrom-linux-gnueabi/bin/
CC=${CROSS}gcc
OBJCOPY=${CROSS}objcopy

app.bin: app.elf
	${OBJCOPY} -O binary $^ $@ 

app.elf: app.S app.c
	${CC} -Wall -nostdlib $^ -o $@ -T app.lds

Using with qemu

Terminal 1:

~/tmp % wget http://meshy.org/~ato/upload/bare-metal-moko.tar.gz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  3322  100  3322    0     0   4156      0 --:--:-- --:--:-- --:--:--  8384
~/tmp % tar -zxf bare-metal-moko.tar.gz 
~/tmp % cd bare-metal-moko 
~/tmp/bare-metal-moko % make
/mnt/oe/openmoko/build/tmp/cross/arm-angstrom-linux-gnueabi/bin/gcc -Wall -nostdlib app.S app.c -o app.elf -T app.lds
/mnt/oe/openmoko/build/tmp/cross/arm-angstrom-linux-gnueabi/bin/objcopy -O binary app.elf app.bin 

Terminal 2:

/mnt/oe/openmoko/build/qemu % cp ~/tmp/bare-metal-moko/qemu-telnet.sh openmoko
/mnt/oe/openmoko/build/qemu % ./openmoko/qemu-telnet.sh 
QEMU waiting for connection on: localhost:1200,server

Terminal 1:

~/tmp/bare-metal-moko % kermit -y download.kerm
 DNS Lookup...  Trying 127.0.0.1...  Reverse DNS Lookup... (OK)
 localhost.localdomain connected on port 1200
ÿûÿûÿûÿý
        
U-Boot 1.3.2-rc2 (May 22 2008 - 01:06:44)
                                         
I2C:   ready
DRAM:  128 MB
NAND:  64 MiB
Found Environment offset in OOB..
Video: 640x480x8 31kHz 59Hz      
                           
NAND read: device 0 offset 0x244000, size 0x5000
                                                
Reading data from 0x248e00 -- 100% complete.
 20480 bytes read: OK                       
USB:   S3C2410 USB Deviced
In:    serial             
Out:   serial
Err:   serial
GTA01Bv4 # loadb 35000000
## Ready for binary (kermit) download to 0x35000000 at 115200 bps...
#                                                

# Total Size      = 0x00000064 = 100 Bytes
## Start Addr      = 0x35000000           
GTA01Bv4 # go 35000000         
## Starting application at 0x35000000 ...

Terminal 2:

...
neo_bl_switch: LCD Backlight now on.
neo_bl_switch: LCD Backlight now off.
neo_bl_switch: LCD Backlight now on.
neo_bl_switch: LCD Backlight now off.
neo_bl_switch: LCD Backlight now on.
neo_bl_switch: LCD Backlight now off.
neo_bl_switch: LCD Backlight now on.
...

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