How to run HelloWorld on ARM - c++

Question

I need to run HelloWorld on arm.
I launch:
$ arm-none-eabi-g++ -mthumb -mcpu=cortex-m3 -c test.cpp -o test
$ file test
test: ELF 32-bit LSB relocatable, ARM, EABI5 version 1 (SYSV), not stripped
$ qemu-arm test <br>
Error while loading test: Permission denied

Answer 1

qemu-system-arm -machine help
...
lm3s811evb Stellaris LM3S811EVB
...
From either the lm3s811 datasheet or looking at the source for the stellaris backend on qemu arm hardware. Uart0 base address is 0x4000C000, the data (rx and tx) register is offset 0x000. From experience the qemu backends tend not to bother with the tx buffer being busy...
flash.s
.cpu cortex-m0
.thumb
.thumb_func
.global _start
_start:
.word 0x20001000
.word reset
.word hang
.word hang
.word hang
.word hang
.word hang
.thumb_func
reset:
bl notmain
b hang
.thumb_func
hang: b .
.thumb_func
.globl PUT32
PUT32:
str r1,[r0]
bx lr
uart01.c
void PUT32 ( unsigned int, unsigned int );
#define UART0BASE 0x4000C000
int notmain ( void )
{
unsigned int rx;
for(rx=0;rx<7;rx++)
{
PUT32(UART0BASE+0x00,0x30+rx);
}
return(0);
}
flash.ld
MEMORY
{
rom : ORIGIN = 0x00000000, LENGTH = 0x1000
ram : ORIGIN = 0x20000000, LENGTH = 0x1000
}
SECTIONS
{
.text : { *(.text*) } > rom
.rodata : { *(.rodata*) } > rom
.bss : { *(.bss*) } > ram
}
Yep, the stellaris was the first cortex-m3 in silicon that you could buy and I specified cortex-m0. Basically preventing the thumb2 extensions, or most of them. More portable, can easily change that if you want.
arm-none-eabi-as --warn -mcpu=cortex-m0 flash.s -o flash.o
arm-none-eabi-gcc -Wall -O2 -nostdlib -nostartfiles -ffreestanding -mcpu=cortex-m0 -mthumb -c uart01.c -o uart01.o
arm-none-eabi-ld -o uart01.elf -T flash.ld flash.o uart01.o
arm-none-eabi-objdump -D uart01.elf > uart01.list
arm-none-eabi-objcopy uart01.elf uart01.bin -O binary
then
qemu-system-arm -M lm3s811evb -m 16K -nographic -kernel uart01.bin
and the output is
0123456
ctrl-a then press x to exit qemu. or
qemu-system-arm -M lm3s811evb -m 16K -kernel uart01.bin
then ctrl-alt-3 (3 not F3) and the serial console pops up with the serial output. when you close that serial console qemu closes.
I want to remember someone telling me that the qemu cortex-m3 support is not that good.
the normal arm cores should be well tested as they are used to cross compile for all kinds of arm target boards. not sure exactly which cores are well tested, but you could do thumb stuff if you booted like an arm but did the rest in thumb, boot with
.globl _start
_start:
b reset
b hang
b hang
b hang
reset:
mov sp,#0x20000
bl notmain
hang:
b hang
the machine
versatilepb ARM Versatile/PB (ARM926EJ-S)
has its uart at 0x101f1000, so
for(ra=0;;ra++)
{
ra&=7;
PUT32(0x101f1000,0x30+ra);
}
can build your app with
arm-none-eabi-gcc -Wall -O2 -nostdlib -nostartfiles -ffreestanding -mcpu=arm7tdmi -mthumb -c uart01.c -o uart01.o
change your linker script to be all ram based.
MEMORY
{
ram : ORIGIN = 0x00000000, LENGTH = 32K
}
SECTIONS
{
.text : { *(.text*) } > ram
.bss : { *(.text*) } > ram
}
and then
qemu-system-arm -M versatilepb -m 128M -nographic -kernel hello.bin
(hmmm, does this load at 0x0000, or 0x8000?, shouldnt be too hard to figure out)
you can get mostly the thumb feel of a cortex-m (an m0 basically not an m3, you can find an armv7-a machine you can probably run thumb2 built code (still boots like an arm not a cortex-m)). for example
realview-pb-a8 ARM RealView Platform Baseboard for Cortex-A8
Can probably use newlib almost as is, need to change the crt0.s or whatever it is called these days to boot like an arm not a cortex-m. The rest can build using armv7m and in theory will work.
And or start with the stellaris and just make your own hw support for whatever your real target is and fix the cortex-m3 core if/when you find problems.