LED blinking in assembler for STM32F103C8T6

[JerryMC22]

Hello,

I am trying small example LED blinking written in assembly only - see below. LED is placed to PB15. I am able to compile the program without error using this commands:

arm-none-eabi-gcc -save-temps -nostdlib -nostartfiles -mcpu=cortex-m3 -ffreestanding -O2 led-stm32.s -o led-stm32.elf
arm-none-eabi-objcopy -O binary led-stm32.elf led-stm32.bin

I am using "gcc-arm-none-eabi-10.3-2021.10-win32.exe". I am able to write the program to processor STM32F103C8T6 using STLINKV2, but nothing happend. LED on PB15 is no blinking, LED is no shining. LED is off. .

Can someone help me where is problem ?  :)  Do you (someone) have working example in assembly ?

@@@ led-stm32.asm

@@@ Directives
        .cpu cortex-m3
        .code 16               @
        .syntax unified
        .global _start
        .align 2

@@@ Equates
        .equ GPIOB_CRH,   0x40010C04
        .equ GPIOB_ODR,   0x40010C0C
        .equ RCC_APB2ENR, 0x40021018
        .equ STACKINIT,   0x20005000

        .equ LEDDELAY,    0x4E20  @20000

.section .text
         .org 0

@@@ Vectors
vectors:
        .word STACKINIT         @ stack pointer value when stack is empty
        .word _start + 1        @ reset vector (manually adjust to odd for thumb)
        .word _nmi_handler + 1  @
        .word _hard_fault  + 1  @
        .word _memory_fault + 1 @
        .word _bus_fault + 1    @
        .word _usage_fault + 1  @

_start:

        @@ Enable the Port B peripheral clock by setting bit 4
        ldr r6, = RCC_APB2ENR
        mov r0, #0x08
        str r0, [r6]

        @@ Set the config and mode bits for Port B bit 15 so it will
        @@ be a open drain output (up to 8 MHz) by setting bits 19-16
        @@ to '0110'.

        ldr r6, = GPIOB_CRH
        ldr r0, = #0x64444444  @ 0110 0100 0100 0100 0100 0100 0100 0100
        str r0, [r6]

        @@ Load R2 and R3 with the "on" and "off" constants
        mov r2, #0              @ value to turn on LED
        mov r3, #0x8000         @ value to turn off LED

        ldr r6, = GPIOB_ODR    @  point to Port B output data register

loop:
        str r2, [r6]           @ clear Port B, pin 15, turning on LED
        ldr r1, = LEDDELAY
delay1:
        subs r1, #1
        bne delay1

        str r3, [r6]           @ set Port B, pin 15, turning off LED
        ldr r1, = LEDDELAY
delay2:
        subs r1, #1
        bne delay2

        b loop                 @ continue forever

_dummy:                        @ if any int gets triggered, just hang in a loop
_nmi_handler:
_hard_fault:
_memory_fault:
_bus_fault:
_usage_fault:
        add r0, #1
        add r1, #1
        b _dummy

[Peter BENSCH]

I haven't checked your code yet due to time constraints, but you can use my ASM example that I once created for STM32G4 and the STM32CubeIDE as a guide. As Cortex-M4 and Cortex-M3 are very similar, you only need to adapt the ASM syntax to your toolchain and check the register addresses.

Hope that helps?

Regards
/Peter