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Q: Why ARM generates undefined instruction exception but PC and instruction are both OK

Dear All,

I have met some problem which holds me for almost 2 weeks. I worked on some ARM926EJ-S based chip. The code sometime can run up to 2-3 days with no problem, but sometime after few hours running, ARM generated "undefined instruction" exception. I use the ICE debugger to trace the problem, the value in "lr" is good, in terms of it is within well defined code area. So I did one experiment, in the "undefined exception handler", I just simply set the PC back to the "lr", and the code can resume without any problem. In my case, I turn on the Icache and Dcache.
Does anyone have the similar experience before? or Any idea? Thanks a lot!

Ys1234

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Charlie Jung over 12 years ago

Note: This was originally posted on 7th March 2012 at http://forums.arm.com

Can you read back I-cache content when it hits the undefined exception?
When you read the instruction pointed by LR through the debugger, it would be re-loaded from the external memory then you should see the different instruction than the one I-cache line.

Regards,
Charlie
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Charlie Jung over 12 years ago

Note: This was originally posted on 7th March 2012 at http://forums.arm.com

Can you read back I-cache content when it hits the undefined exception?
When you read the instruction pointed by LR through the debugger, it would be re-loaded from the external memory then you should see the different instruction than the one I-cache line.

Regards,
Charlie
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