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

yuan shao
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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  • Note: This was originally posted on 20th March 2012 at http://forums.arm.com

    Thanks, Charlie. I will test more as you suggested.

    ys1234

    Hi YS1234,

    For checking external memory, I'd like to suggest relocation of your code to different address of external memory.
    One more thing for checking internal path or cache line fill, you could add one or two 'NOP' prior to the problematic instruction and see what's different.

    Thanks,
    Charlie
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  • Note: This was originally posted on 20th March 2012 at http://forums.arm.com

    Thanks, Charlie. I will test more as you suggested.

    ys1234

    Hi YS1234,

    For checking external memory, I'd like to suggest relocation of your code to different address of external memory.
    One more thing for checking internal path or cache line fill, you could add one or two 'NOP' prior to the problematic instruction and see what's different.

    Thanks,
    Charlie
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