Luis A. Loeff <PICLIST@mitvma.mit.edu> wrote:

> I am not being able to explain why a snippet of code fails
> permanently. May be somebody can explain
>
>
> 0121   234D           00386 TONESTOP    CALL        READ80
> 0122   0782           00387             ADDWF       PCL, F
> 0123   2A71           00388             GOTO        REFI
> 0124   080F           00389             MOVF        BREG, W
> ....
>
> I am positive that the problem has to do with computed goto's
> using addwf pcl, f  because the following code solved the problem
> immediately
>
> tonestop    call        read80
>             movwf       aux1   ; NEW
>             btfss       aux1, 0  ; NEW
>             goto        refi
>             movf        breg, w
> ....
>
> Page boundaries don't seem to be the problem as the original code
> was at addresses 0121 through 012A

Luis:

If W is always guaranteed to be either 0 or 1 after the CALL, then
page boundaries clearly ARE the problem; there's no other
explanation, especially since interrupts can't be happening.

If you don't want to use the "aux1" register, you can do:

    CALL    READ80
    XORLW   0
    BZ      REFI
    MOVF    BREG,W

-Andy

=== Andrew Warren -- aiw@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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