CMP without S flag generates an error

Whilst comparing the differences in physical processor behaviour for a comparison without the S flag (CMP, CMN, TST, TEQ), I discovered RPCEmu reports an opcode error instead of processing the instruction correctly.

For reference, the behaviour should be:

ARM610/710 – becomes a NOP
StrongARM – branch to the undefined instruction hardware vector

Repro code:

P%=&9000:[MOV R0,#0:CMP R0,#0:CMP R0,#1:MOVNE R0,#1:MOV PC, R14:]
A%=USR &9000:!&9008=&E3400001:SYS "OS_SynchroniseCodeAreas",0:PRINT (USR &9000)-A%

If a missing S bit changes the instruction to a NOP, the result is -ve.

Aren’t you missing an OS_SynchroniseCodeAreas call once you’ve poked the instruction? That could be throwing off your results for both native and emulated StrongARM.

And isn’t this an issue for the RPCEmu mailing list?

If you trying out bits of code – why not use !Zap.

Go to code mode – enter in ’cmp r0,#0 etc – then save.

If you are using a 26bit OS use !ArmDebug to step through it.

If a 26 or 32bit OS – !DeskDebug works well.

Aren’t you missing an OS_SynchroniseCodeAreas call once you’ve poked the instruction?

Good point, yes. I keep forgetting about that pesky SA cache! Unfortunately I don’t have access to an SA for a while to retest.

And isn’t this an issue for the RPCEmu mailing list?

I usually post issues on here, if it’s not the right place I can only apologise. That may explain why the issues I’ve raised with permission faults last year haven’t been resolved yet.

If you are using a 26bit OS use !ArmDebug to step through it.

I do use !ArmDebug, however I’m not convinced it does actually execute the instruction, I suspect it emulates it in some way as some instructions don’t execute correctly – does anyone have the source code or know how to contact the author? I’d love to amend it so it works on a 32bit OS and works under ADFFS.

http://members.upc.nl/t.boogaert6/ !ARM_Debug 1.35 (June 2002)

email down at the bottom of the page

You might not have the last version – I suggest you ask.