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UXTB only Thumb2?

Samar Samar
Note: This was originally posted on 12th February 2009 at http://forums.arm.com

Hi All,

Arm9 crashed on UXTB instruction because it is not able to decode it. It caused Undef-Instruction exception.

I have been trying to find if UXTB which is a Thumb2 instruction (only supported on ARMv7 onwards) is also supported by Thumb. In other words can I actually use UXTB instruction on Arm9 (ARMv5)?

Thanks a lot,
Samar
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  • 0 Arm Employee Badge
    Note: This was originally posted on 12th February 2009 at http://forums.arm.com

    Samar,

    In ARM state, ARM9 can peform the equivalent to UXTB simply using the immediate variant of AND:
    [font="Courier New"]AND r0,r0,#0xFF[/font]

    ARM9 only implements the v5T/v5TE variant of Thumb, which does not support UXTB, and for which there is no immediate variant of AND; thus the equivalent to UXTB in Thumb state on ARM9 is:
    [font="Courier New"]LSLS r0,r0,#24
    LSRS r0,r0,#24[/font]

    hth
    s.
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  • 0 Arm Employee Badge
    Note: This was originally posted on 12th February 2009 at http://forums.arm.com

    Samar,

    In ARM state, ARM9 can peform the equivalent to UXTB simply using the immediate variant of AND:
    [font="Courier New"]AND r0,r0,#0xFF[/font]

    ARM9 only implements the v5T/v5TE variant of Thumb, which does not support UXTB, and for which there is no immediate variant of AND; thus the equivalent to UXTB in Thumb state on ARM9 is:
    [font="Courier New"]LSLS r0,r0,#24
    LSRS r0,r0,#24[/font]

    hth
    s.
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