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I recently ended up in the Default_Handler in my stm32 project and couldn't figure out what was casing it:

  .section .text.Default_Handler,"ax",%progbits
Default_Handler:
Infinite_Loop:
    b   Infinite_Loop <--- here!

By default, a lot of interrupts are mapped to the default handler and the only way I could figure out what the actual interrupt reason was, would be to write handlers for all the interrupts (60+) and pause the code in the debugger. Bah!

I didn't find a good answer googling, so I thought I document the solution for others (or most likely myself in 6 months...)

Guz
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1 Answers1

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So, it turns out there are some registers in the NVIC (interrupt controller) that we could use:

NVIC registers

The above is from the STM32CubeIDE debugger. NVIC_IABRX contains a bitmask of the currently active interrupts and I can see that NVIC_IABR1 has a non-zero bit (it's 0x1000).

Each IABR reg is 32 bits wide, so with some simple bit counting I conclude that the interrupt source is 32+12 = 44. Now I need to look at the datasheet for my mcu (an stm32wb55) so see what that corresponds to:

datasheet excerpt

Aha, so it's the IPCC that's causing the interrupt! To double check, I added a handler for this specific interrupt

void IPCC_C1_RX_IRQHandler(void)
{

}

And it got called!

Note: I initially just had a look at interrupt vector in the startup_stm32xxx.s file and counted from the start of that but that didn't work out since the first few interrupts are not included in the NVIC_IABRX registers.

Guz
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