I would argue that “IRQ handling” should just be standard v8M hardware behaviour for the following rational:

• IRQ routines should be short and simple by nature – it is therefore relative easy to fully verify it and ensure that there are no side effects.
• IRQ should be therefore executed in handler mode using MSP, no MPU protection, only protection via SAU, PPC, MPC.

 

Another reason of this relaxed approach is the usage of DMA.

• DMA is frequently controlled by IRQ
• DMA also bypasses MPU, therefore same behaviour as IRQ.

 

Overall this approach ensures simple, fast IRQ execution (sales argument of v8M) and reduces risk software glitches in TF-M Core.

What is wrong with that approach?

 

Reinhard

 

 

 

 

 

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