> main:
>   bsf STATUS,RP0
>   clrf TRISA
>   bcf STATUS,RP0
>
>   call Thesub           ; call it and then fall through into it
>
> Thesub:
>   movlw 0x01
>   xorwf PORTA,f
>   retlw 0               ; this should jump to Thesub according to your
>                         ; description (pop keeps popping the last value)

I do not see how this construct depends on the (you assume a 12-bit core? =>
2-entry) stack preserving its deepest value. The call pushes 'Thesub' and
jumps to it, stack is now (left is top)
'Thesub', X
the PC executes the subroutine, pops 'Thesub' and returns. stack is now
X, X
execution continues at 'Thesub' (again), at the retlw X is popped an the PIC
goes to never-never.

BTW the above (calling a sub that follows the call) can be a usefull
construct, I used it in the Wisp firmware (or at least it was available in
my include files, I can not find an actual use of it):

; convert w to two hex values in w, high nibble first
convert_w_to_hl_hex macro
 local same = 1
 local w = 0
 cblock
  _file_1#v($)
 endc
 local temp = _file_1#v($)
 local do_it
 movwf temp
 call do_it
 swapf temp, same
do_it
 swapf temp, w
 andlw H'0F'
 endm

;use
send_w_hl
   convert_w_to_hl_hex
   send_w
   ret

Wouter van Ooijen

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