STM32F103xx Assembly - unable to run application

[Praveen1]

I am "Learning" assembly, So I have tried to program my stm32f103 in assembly (a simple program to blink a led). The problem is that the program runs when uploaded using st-flash utility. But, If I press reset button, the program stops working.

Here are few things that I debugged in STM32CubeProgrammer.

1. The program seems runs if do a reset from the programmer but not on board.
2. I get a unable to run error If I try to run the CPU from CubePrg after manual button reset.
3. Moreover the Program Counter register seems to jump to 0xFFFFFFFE in the above case (Not always).

I am using Ubuntu and Nucleo-64 board.

PS. I didnt use any startup_*.s file. Instead placed the 2 vector address by using word and main program at 0x08000200 using .org directive

EDIT:

The program counter now always goes to 0.

Code:

.equ RCC_BASE, 0x40021000
.equ APB2ENB, RCC_BASE + 0x18
.equ GPIOA_BASE, 0x40010800
.equ GPIOA_CONF_L, GPIOA_BASE + 0x0
.equ GPIOA_BSSR, GPIOA_BASE + 0x10
.equ GPIOA_ODR, GPIOA_BASE + 0xC
 
.syntax unified
.cpu cortex-m3
.thumb
 
// Global memory locations.
.global reset
.word 0x20001000
.word reset
 .text
 .entry
 
reset: .proc
 ;LDR r3, =_estack
 ;MOV sp, r3
 push {r7}
 ADD r7, sp, #0
 B _main
 
_main:
 // Enable Clock APH
 LDR r3, =APB2ENB
 LDR r2, [r3]
 ORR r2,r2,#0x4
 STR r2, [r3]
 // Reset Pin PA5
 LDR r3, =GPIOA_BSSR
 LDR r2, [r3]
 MOV r2, #0x20
 STR r2, [r3]
 //Set PinMode PA5 as OUTPUT
 LDR r3, =GPIOA_CONF_L
 LDR r2, [r3]
 MOV r2, #0x100000
 STR r2, [r3]
 // Set Default High on PA5
 LDR r3, =GPIOA_ODR
 LDR r2, [r3]
 MOV r2,#0x20
 STR r2, [r3]
 mov r3, #0
 B loop
 .endp
 
loop:
 LDR r3, =GPIOA_ODR
 LDR r2, [r3]
 ORR r2,r2,#0x20
 STR r2, [r3]
 MOV r4,#0xFF40
 BL _delay
 LDR r3, =GPIOA_ODR
 LDR r2, [r3]
 AND r2,r2,#0xFFFFFFDF
 STR r2, [r3]
 MOV r4,#0xFF40
 BL _delay
 B loop
 
_delay:
 SUB r4,r4,#0x1
 CMP r4,#0
 BNE _delay
 BX lr
 .align
 .end

  Finally, got it working. The problem is the address of the reset handler. I set second vector address to reset_label+1. But, why?

Still curious how it worked the first time (when uploaded).

[Peter BENSCH]

There are some Youtube videos that were originally created for a workshop to support the transition from simple old 8-bit architectures to modern 32-bit Cortex-M architectures. You will also find the material of the workshop in the comment section of the videos. Video 5 in particular contains some interesting approaches on how to write an assembler program very easily - without a startup_*.s file, as you would like to do.:

• Moving from 8 to 32bit workshop - 3 STM32 hardware getting started
• Moving from 8 to 32bit workshop - 4 STM32 startup
• Moving from 8 to 32bit workshop - 5 STM32 software getting started

Good luck!

/Peter

[Tesla DeLorean]

>>But, If I press reset button, the program stops working.

As no code is presented, I'd guess you're not enabling one or more clock on the RCC that the debugger is doing, but are off by default out of reset.

GPIOA?

[Praveen1]

I am Sorry. I forgot to paste the code. Anyway, I have Uploaded it now.