Setting the Interrupt Priority on an LPC55S69

PhilV · ‎10-12-2023

On LPC55S69 the Peripheral Config tool for the FlexComm interface allows you to either not "Enable priority initialization", or to enable it and set a value.

I can see from the reference manual that permissible values are 0-7 and the relevant value is written to a specific section of the NVIC->IPRn registers.

However when writing the priority there doesn't seem to be any "enable" or "disable" for the priority, it just literally writes the priority value (0-7) to the register location, so presumably this means that the prioritization is always enabled, and the 'enable or not' shown in the config tool is just a UI thing...

If that is the case, and since ALL the IPR registers have reset value of 0, then does this mean that everything is set to the highest priority by default, and your only option is to de-priorities certain interrupts?
So if I actually want 2 interrupts to have higher priority than the rest, what I actually need to do is deprioritise everything else (that has interrupt enabled?)

xiangjun_rong · ‎10-12-2023

Hi,

You are right, for the Contex-M33 core, each interrupt source has priority register(one Byte) and one enabling bit in the ISERx register, you have to set the bit if you want the interrupt source to generate interrupt.

For the ISERx register, pls refer to the Table4-35 in cortex-M33 user guide, which I attached.

Hope it can help you

BR

XiangJun Rong

PhilV · ‎10-13-2023

Thanks for your reply, I am aware of how to enable the interrupt, and how to set priority, my question was more around whether I was correct in my thinking that ALL interrupts are by default at the highest interrupt level, and if I wish for any interrupt to have higher priority than the rest, then I would need to LOWER the priority of every other (enabled) interrupt, since I cannot make just the ones I am interested in a higher priority (since the default is already highest).

xiangjun_rong · ‎10-13-2023

Hi,

Yes, the default value of priority register is zero after Reset for LPC55xx, the 0 is of the highest priority.

You can reduce the logic interrupt priority by assigning a non-zero value to the priority register.

Hope it can help you

BR

XiangJun Rong