Openocd / GDB Cortex-M3调试问题

Question

i have written a very simple program to turn on the 2 LEDs (GPIO port B) on the STM32L-discovery kit.

I am using GNU toolchain and openocd for my debugging.

Compilation and linking went ok. I linked the code such that the LMA and VMA are in the ram region.

I opened the .elf in GDB-insight, inserted some breakpoints and ran openocd with 'openocd-x64-0.7.0 -f stm32ldiscovery.cfg'

At gdb prompt, i ran the following:

(gdb)target remote localhost:3333

(gdb)monitor reset halt

(gdb)load

(gdb)continue

(gdb)stepi

...

Full source code and object files here

====================...part of source code...===============================

const1: .word 0x40020400    @@GPIOB base mode register

const2: .word 0x55555555

const3: .word 0x40020414    @@GPIOB base output register

const4: .word 0x0000FFFF

...
...
...

reset_handler:

    ldr r0, =const2
    ldr r2, [r0]    @r2=const2
    ldr r0, =const1
    ldr r1, [r0]    @r1=const1  
    str r2, [r1]                    @@set mode to output

    ldr r0, =const4
    ldr r2, [r0]    @r2=const4
    ldr r0, =const3
    ldr r1, [r0]    @r1=const3  
    str r2, [r1]                    @@set output register to 1

loop:
b loop

===================================================

Basically, i set the GPIO port B ( 0x40020400 ) to output mode ( 0x55555555 ) and then set '1's ( 0x0000FFFF ) to the port B output register ( 0x40020414 )...

I was able to step through the assembly instructions and see that the registers (r0, r1 ...) are updating to the expected values...

but when i came to str r2, [r1] and str r2, [r1] which are basically writing new values to the peripheral registers, i found that these peripheral memory locations ( 0x40020400 and 0x40020414 ) are not updating to the new values ( 0x55555555 and 0x0000FFFF ).

From gdb prompt, I tried running monitor mdw 0x40020400 and confirmed that this memory location is not having the new value 0x55555555 . I also tried monitor mww 0x40020400 0x55555555 to write the memory location but to no avail... i also tried set *0x40020400 = 0x55555555 but to no avail also...

Can anyone help me out? is it some openocd/gdb configurations or settings i got wrong?

Answer 1

Ok, found the problem.

I did not enable the GPIOB clock.

I enabled it through the RCC_AHBENR register before accessing/modifying the GPIOB registers as above code... Now it works.