STM32MP1 interrupt causes undefined exception in ARM mode (but works in thumb)

[bsvi]

I modified an FSBL example to get to the root of the problem (everything else being as in the example).

volatile int rrr = 0;
void SGI0_IRQHandler(void) {
    while (1) {
        rrr++;
    };
}

int main()
{
  HAL_Init();
  SystemClock_Config();

  IRQ_Disable(SGI0_IRQn);

  IRQ_SetPriority(SGI0_IRQn, 0);
  IRQ_Enable(SGI0_IRQn);

  while(1) {
	  GIC_SendSGI(SGI0_IRQn, 1, 0);
  }
}

This works perfectly in thumb mode, but when I switch to ARM (that probably should give slight performance boost for my DSP task), the interrupt is stuck in Vectors section, without doing anything.

The LR is weird, and I cant get my head around how is it possible that is has LR = 0x2ffe0106 (not multiple of 4)

As if the core switched to thumb mode without address being odd and started executing instructions in 16 bit mode.

Thanks for any advice :)

[Olivier GALLIEN]

Hi @bsvi ,

Please confirm you are on baremetal MP13 solution on DK board here ?

Thanks 

Olivier 

[PatrickF]

Hi @bsvi 

you should refer to ARM documents to understand how interrupt are handled.

https://developer.arm.com/documentation/ddi0406/latest/

https://developer.arm.com/documentation/den0013/d/Exception-Handling/Exception-handling

Regards.

[bsvi · Accepted solution]

Found the cause, I it's actually a bug in ST's code. So, the reason is that all startup_stm32mp135fxx_ca7.c files unconditionally enable interrupt handling in thumb mode with this line:

"ORR R0, R0, #(0x1 << 30) \n" /* Set TE bit to take exceptions in Thumb mode */

While startup_stm32mp135fxx_ca7_azurertos.c do it depending on ARM_MODE define.