微處理器 - Broadcom BCM2835 (Raspberry Pi) - Assembly - LED

參考資料：
https://elinux.org/RPi_Software#ARM
https://github.com/dwelch67/raspberrypi
https://github.com/raspberrypi/firmware
https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf

LED連接到GPIO-29


暫存器


Alternate Function


GPIO SET


GPIO CLR


main.s

    .global _start

    .equiv GPFSEL2, 0x20200008
    .equiv GPSET0,  0x2020001c
    .equiv GPCLR0,  0x20200028

    .arm
    .text
_start:
  b reset
    b .
    b .
    b .
    b .
    b .
    b .
    b .
         
reset:
    ldr r0, =GPFSEL2
    ldr r1, =(1 << 27)
    str r1, [r0]

0:
    ldr r0, =GPSET0
    ldr r1, =(1 << 29)
    str r1, [r0]
    ldr r2, =0x100000
1:
    subs r2, #1
    bne 1b
    
    ldr r0, =GPCLR0
    ldr r1, =(1 << 29)
    str r1, [r0]
    ldr r2, =0x100000
1:
    subs r2, #1
    bne 1b
    b 0b
    .end

P.S. 實體位址是0x20000000，虛擬位址是0x7e000000

main.ld

MEMORY {
    RAM : ORIGIN = 0x8000, LENGTH = 0x10000
}

SECTIONS {
    .text : { *(.text*) } > RAM
    .bss : { *(.bss*) } > RAM
}

Makefile

all:
	arm-none-eabi-as -mcpu=arm1176jzf-s -o main.o main.s
	arm-none-eabi-ld -T main.ld -o main.elf main.o
	arm-none-eabi-objcopy -O binary main.elf kernel.img

clean:
	rm -rf kernel.img main.o main.elf

編譯

$ make
    arm-none-eabi-as -mcpu=arm1176jzf-s -o main.o main.s
    arm-none-eabi-ld -T main.ld -o main.elf main.o
    arm-none-eabi-objcopy -O binary main.elf kernel.img

安裝步驟：
1. 將Micro SD格式化成FAT32
2. 將https://github.com/steward-fu/website/releases/download/pi-zero/bootcode.bin放到Micro SD根目錄
3. 將https://github.com/steward-fu/website/releases/download/pi-zero/start.elf放到Micro SD根目錄
4. 將kernel.img放到Micro SD根目錄
5. 插入Micro SD到Raspberry Pi Zero

完成