NVIC and Piority Grouping in STM32 after reset

My guess is that this error in documentation was only spotted (and fixed) on more modern versions of the manual. For example PM0214 Rev 8 (stm32f4) shows 0b0xx gives group priority bits 7:4, not just 0b011

Check ARM TRM or simply print them out to confirm.

Expect they reset to zero, but shouldn't be hard to determine or to set to what you actually want / need.​

I have read ARM TRM and according to that if PRIGROUP is b000 number of pre-emptition piorities should be 128 and 2 subprorities but STM32 has only 16 levels so there is something wrong?!

"Implementations having fewer than 8-bits of interrupt priority treat the least significant bits as zero."

STM32's have 4 bits of interrupt priority which gives at most 16 preemption levels, 0-15 and no sub-priorities. This is the default mode of ST HAL library.

You can select less than 4 bits of preemption then remaining bits will be used for sub-priority.

Many ST examples use priority value 0 or (0, 0) - it will work with any PRIGROUP value, valid or not, even all zeros.

The default reset value already makes all 16 levels as group (preemption) priorities. Just do not change it...