STM32 unimplemented interrupts

FLast.17.70 · ‎2018-02-20

Posted on February 20, 2018 at 09:33

All of the STM32 devices have unimplemented interrupt numbers, for example on the STM32F767 I am currently using, the last used interrupt MDIOS_IRQn is interrupt number 109.

So is it possible to use the next one, number 110, as a user software interrupt? Obviously there is no peripheral device connected to this interrupt line so there is no danger of a spurious interrupt request, but what's stopping us from defining our own interrupt as

MYOWN_IRQn = 110

And then enabling it and disabling it with NVIC_EnableIRQ(), adding another entry to the interrupt vector table in startup_stm32f767xx.s and using it as a user-defined software interrupt?

AvaTar · ‎2018-02-20

Posted on February 20, 2018 at 09:53

ARM implemented the Supervisor Call (SVC) instruction for that very purpose.

FLast.17.70 · ‎2018-02-20

Posted on February 20, 2018 at 11:27

>>

ARM implemented the Supervisor Call (SVC) instruction for that very purpose.

Yes, but still, the question is valid.

(Actually, I have another reason for doing this. I would like to install a 'dummy' interrupt that I can freely execute without any effect on any peripherals. Yes, I could hijack SVC for this but I don't want to abuse that feature.)

Andrew Neil · ‎2018-02-20

Posted on February 20, 2018 at 11:31

But how would you actually 'trigger' this interrupt ?

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A complex system designed from scratch never works and cannot be patched up to make it work.

Tesla DeLorean · ‎2018-02-20

Posted on February 20, 2018 at 12:34

Likely bits not implemented in NVIC, best to just reuse existing slots you aren't actually using, ie CAN2 or TIM19

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waclawek.jan · ‎2018-02-20

Posted on February 20, 2018 at 11:47

By setting the respective bit in NVIC_ISPRx, of course, maybe through CMSIS' NVIC_SetPendingIRQ().

However, it may well be that there's no hardware for these interrupts in NVIC.

JW

henry.dick · ‎2018-02-20

Posted on February 20, 2018 at 13:01

Yes, it will work. You can simply set the flag, assuming that the nvic is set up somewhere else. Some modifications to the start up file may be necessary.

The same works for implemented but unused interrupts.

And on other chips too.

Andrew Neil · ‎2018-02-20

Posted on February 20, 2018 at 12:08

waclawek.jan wrote:

it may well be that there's no hardware for these interrupts in NVIC.

Indeed - there's the catch!

Relying upon undocumented / unsupported features is never a Good Thing ...

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

AvaTar · ‎2018-02-20

Posted on February 20, 2018 at 12:28

Indeed, the vector table differs between sub variants, as the officially implemented peripherals differ.

Be prepared for surprising results.

There have been STM32s around for years with more Flash than documented, due to defect-related 'downgrading' in the factory functional tests.

Andrew Neil · ‎2018-02-20

Posted on February 20, 2018 at 12:37

AvaTar wrote:

There have been STM32s around for years with more Flash than documented, due to defect-related 'downgrading' in the factory functional tests.

Not just STM32 - that's a common industry practice

Car manufacturers, white goods manufacturers, et al, do similar things..

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.