On Fri, 25 Apr 1997 08:15:27 -0600 Ed Todd <edtodd@SNI.NET> writes:
>I use the push down nature of the CALL stack quite a bit to optimize
>code
>space.

        It sounds like you are relying on stack wrap-around, right?  It
seems dangerous to me to leave stuff on the stack since I don't really
keep track of who's calling what from where.  If there's some extra
garbage on the stack and I do a return... watch out!

>For example, I have a timeout procedure, called from several
>locations on different pages.  The structured programming method of
>doing
>this would be:
>        CALL    TIMEOUTPROC
>        IF (FLAG1)
>                GOTO    RETRY           // timeout, resend message
>        IF (FLAG2)
>                GOTO    JAMMING // signal jamming error recovery
>        IF (FLAG3)
>                GOTO    SLEEP           // no traffic, go back to
>sleep
>Duplicating this logic gets expensive in code space.  It is even worse
>if
>the test is made during a call:

        Instead of setting flags, how about returning a unique state
number, then using a jump table.

JumpTable
        movlw   high(JumpTable)
        movwf   pclath          ; Set up high PC latch for
jump
        movfw   SystemState     ; Get state (0..3)
        andlw   0x03            ; Mask leaving 2 lsb
        addwf   pcl,1           ; Add to PC
        goto    NoError         ; State 0 - No error, so
continue
        goto    Retry           ; State 1 - Go retry
        goto    Jamming         ; State 2 - It's jammed
NoError                         ; State 3 - Here same as state 0,
no error
        sleep




Harold