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Cortex-M3 Thread mode stack

Note: This was originally posted on 25th August 2010 at http://forums.arm.com

Gentlemen

I am wondering if, while processing an arbitrarily nested ISR, there is a reliable way to determine which stack thread mode is using (process or main). The CONTROL register seems not appropriate since the SPSEL bit is reserved in Handler mode. The only other place I can think of is the (stacked) link register of the ISR preempting thread mode. But how do I get to it? We don't know the sizes of stack frames in between this and the current ISR. I must have missed something...

Thanks
Marcus

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Joseph Yiu over 12 years ago

Note: This was originally posted on 25th August 2010 at http://forums.arm.com

Hi Marcus,

I see. Yes, trying to do that is difficult.
But then when you have untrust ISR, it is likely that you want this ISR to use the process stack only.
The thread could be running with main stack or process stack, it should still work.

regards,
joseph
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Joseph Yiu over 12 years ago

Note: This was originally posted on 25th August 2010 at http://forums.arm.com

Hi Marcus,

I see. Yes, trying to do that is difficult.
But then when you have untrust ISR, it is likely that you want this ISR to use the process stack only.
The thread could be running with main stack or process stack, it should still work.

regards,
joseph
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