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UXTB only Thumb2?

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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Peter Harris over 12 years ago +1 verified

Note: This was originally posted on 12th February 2009 at http://forums.arm.com UXTB was added in ARMv6 for both ARM and Thumb. It is also in Thumb2, as Thumb2 is a superset of the original Thumb instruction...

0 Samar Samar over 12 years ago

Note: This was originally posted on 13th February 2009 at http://forums.arm.com

The Thumb quick reference card outlines which instructions are available in each architecture, and can be found here : [url="http://infocenter.arm.com/help/topic/com.arm.doc.qrc0006e/QRC0006_UAL16.pdf"]infocenter.arm.com/.../url]

s.

Thanks everyone for replying. That is very helpful.

Samar
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+1 Peter Harris over 12 years ago

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

UXTB was added in ARMv6 for both ARM and Thumb. It is also in Thumb2, as Thumb2 is a superset of the original Thumb instruction set.

> In other words can I actually use UXTB instruction on Arm9 (ARMv5)?

No. ARMv6 is ARM11 upwards.
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0 Simon Craske over 12 years ago

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 Simon Craske over 12 years ago

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

The Thumb quick reference card outlines which instructions are available in each architecture, and can be found here : [url="http://infocenter.arm.com/help/topic/com.arm.doc.qrc0006e/QRC0006_UAL16.pdf"]http://infocenter.arm.com/help/topic/com.a...C0006_UAL16.pdf[/url]

s.
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