>> Should the contents of W survive a subroutine return?
>
> (if saved to a temp file and then restored) yes
>
>> Should they survive a call to a subroutine that only executes "return"
>
> AFAIK, yes

I don't have the full context here, but I generally assume that W gets
trashed on call and return to/from global subroutines.  This is because W
may be used to set PCLATH.  After the return, W may again be used to restore
PCLATH to the current page.  See my GCALL, GCALLWR, and GCALLR macros in
STD.INS.ASPIC at http://www.embedinc.com/pic.  These differ in how the value
in W is treated on the return from the subroutine.


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