Does zip work on a 32-bit RISC OS ?

Adrian Lees adrian at
Tue Oct 11 16:20:29 PDT 2005

On Tue, 11 Oct 2005 you wrote:

> I just see non 32-bit APCS code in GCCSDK zip (sendbits.s) file so this
> probably means that the RISC OS zip binary doesn't work or work well on
> a 32-bit RISC OS version (Iyonix, A9).  Can someone acknowledge this ?

Whilst use of MOV/S/ pc,lr and LDMFD ...pc}/^/ are technically
UNPREDICTABLE in User (and System) mode they are harmless on both
the XScale and the ARM9, based on my experience and some quick
tests. (In fact the first release of OpenVector and friends ran
with many such instructions still in place due to an oversight on
my part.)

Unintentionally using those instructions in SVC mode is quite a different
matter! (IRQ handler are not required to preserve SPSR_svc when calling


PS. I have not tested the zip program but I'd be surprised if that
code gives any problems.

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