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Division by non-power-of-2 hits into exception

Zhe Cui

Hi there,

I was using Codewarrior targeting Cortex-R4 CPU to build Firmware. When doing a division coprocessor was used and caused exception.

Here is the division in C:

u8 i, j = 8;

i = j / 3;

Disassembly:

(u8 i, j = 8;)

mov r5, #0x8

(i = j / 3;)

mov r1, #0x3

mov r0, r5

mrc p6, 1, r0, c0, c1, 4

and r4, r0, #0xff

When running mrc, exception occurred.

Does anybody have any idea why it happens? Anyway to disable coprocessor in this operation?

Thanks.

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  • 0 Arm Employee Badge

    Can you check what compiler flags you are using?

    The "mrc p6, 1, r0, c0, c1, 4" is interesting, as it's an access to coprocessor 6.  There isn't (AFAIK) a coprocessor 6 on the Cortex-R4, and accessing a non-existent coprocessor does cause an Undef exception.

    If it's a custom coprocessor on that SoC it may need to be enabled, check with the silicon provider.  Otherwise (and this seems more likely) you might be building for the wrong part - where the part you're building for had the coprocessor and this one doesn't.

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  • 0 Arm Employee Badge

    Can you check what compiler flags you are using?

    The "mrc p6, 1, r0, c0, c1, 4" is interesting, as it's an access to coprocessor 6.  There isn't (AFAIK) a coprocessor 6 on the Cortex-R4, and accessing a non-existent coprocessor does cause an Undef exception.

    If it's a custom coprocessor on that SoC it may need to be enabled, check with the silicon provider.  Otherwise (and this seems more likely) you might be building for the wrong part - where the part you're building for had the coprocessor and this one doesn't.

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