On Tue, 20 Jan 1998 11:45:35 -0500 "Najemy, Daniel"
<DNajemy@IMPS0014.US.DG.COM> writes:
>Thanks Harold - I'm certainly learning this the hard way - you
>solution
>works really well. I was also switching to the incorrect bank as well.
>

        No problem, Daniel.  I KNEW of this problem yet still did not see
it in some of my own code.  In my case, it appeared that an interrupt
routine was corrupting w even though the context (including w) was saved
on going into an interrupt.  I posted the code on the list and someone
pointed out that my disableIRQ actually just put a delay in there to
allow the port to settle.  The problem wasn't the interrupt at all.  So I
changed to code similar to what I sent you.
        I've also done a few macros so I don't have to remember which bit
does what for banks and interrupts.  I think they're real useful.  Here
they are...

;----------------------MACRO
DEFINITIONS------------------------------------------------
DisableIRQ macro
        local DIRQloop          ; Declare local symbol in macro
DIRQloop
        bcf     intcon,gie      ; disable global interrupts
        btfsc   intcon,gie      ; make sure it's clear
        goto    dirqLoop        ; if not, go clear again
        endm
EnableIRQ macro
        bsf     intcon,gie      ; set global interrupt enable
        endm

  cblock                        ; reserve ram for save and restore
context
        isrW            ; Hold registers during ISR
        isrStatus
        isrFSR
  endc
SaveContext macro
; Save register context for isr.  Swaps swap high and low halves of f
with the result going either
; back to f or to w.  Swap is used here because they affect no status
bits.
        movwf   isrW            ; Save W
        swapf   status,w        ; get status in W (including bank
select bits) swapping hi/lo halves
        bcf     status,rp0      ; force to bank 0
        movwf   isrStatus       ; and save swapped status
        movf    fsr,0           ; Get fsr in w
        movwf   isrFSR          ; and save it
        endm
RestoreContext macro
        movf    isrFSR,0        ; get old fsr
        movwf   fsr             ; and restore it
        swapf   isrStatus,w     ; get old status (including bsr
bits) in w, swapping back to normal
        movwf   status          ; restore it
        swapf   isrw,1          ; swap halves in isrw making
them backwards
        swapf   isrw,0          ; swap back to forward and in
W without affecting status
        endm
Bank1   macro
        bsf     status,rp0      ; Set bank select bit
        endm
Bank0   macro
        bcf     status,rp0      ; Clear bank select bit
        endm



Harold