Regulus Berdin wrote:
>
> Hi John/Scott,
>
> Here is my version, somewhat similar to Scott's but the correction and
> the end is more simpler:
>
> (untested)
> cnt16bit:
>         clrf    kz
>         clrf    lo
>         clrf    hi
>
>         movlw   2               ;preset 2 counts
> loop    btfsc   PORTB,7
>          goto   quit1           ;1
>
>         addwf   lo,f            ;inc lo cnt
>         btfsc   PORTB,7
>          goto   quit2           ;2
>
>         rlf     kz,w            ;get carry
>         btfsc   PORTB,7
>          goto   quit3           ;3-2
>
>         addwf   hi,f            ;hi incremented depends on carry
>         btfsc   PORTB,7
>          goto   quit4           ;4-2
>
>         skpc                    ;check if already finished
>         btfsc   PORTB,7
>          goto   quit5           ;5-2
>
>         movlw   7               ;add 7 uncounted tests
>         btfsc   PORTB,7
>          goto   loop6           ;6-2
>
>         btfss   PORTB,7
>          goto   loop
>                                 ;7-2
>
> quit7   incf    kz,f            ;add uncounted tests
> quit6   incf    kz,f
> quit5   incf    kz,f
> quit4   incf    kz,f
> quit3   addwf   hi,f            ;inc hi byte first
>                                 ; bec. not incr in the loop
>
> quit1   incf    kz,w
>         addwf   lo,f
>         skpnc
>          incf   hi,f
>         return
>
> quit2   addwf   hi,f
>         return

And then corrected:

> Sorry, I made a mistake.  This should be:
>
>         incf    kz,w
> adj     addwf   lo,f
> quit2   skpnc
>          incf   hi,f
>         return
>
> quit1   addlw   -1      ;1 test less
>         goto    adj

This still will not work because the value of W is either 0,1 or 7 when
the quit 3 label is encountered. I think a slightly better approach -
that still keeps the spirit of this idea - is to not try to use the
contents of W once the loop has been terminated. Also, another small
problem is that the overflow condition is not checked for outside of the
loop.

If I may:


cnt16bit:
>         clrf    kz
>         clrf    lo
>         clrf    hi
>
>
          movlw   7               ;preset 7 counts

> loop    btfsc   PORTB,7
>          goto   quit1           ;1
>
>         addwf   lo,f            ;inc lo cnt
>         btfsc   PORTB,7
>          goto   quit2           ;2
>
>         rlf     kz,w            ;get carry
>         btfsc   PORTB,7
>          goto   quit3           ;3-2
>
>         addwf   hi,f            ;hi incremented depends on carry
>         btfsc   PORTB,7
>          goto   quit4           ;4-2
>
>         skpc                    ;check if already finished
>         btfsc   PORTB,7
>          goto   quit5           ;5-2
>
>         movlw   7               ;add 7 uncounted tests
>         btfsc   PORTB,7
>          goto   loop6           ;6-2
>
>         btfss   PORTB,7
>          goto   loop
>                                 ;7-2
>
> quit7   incf    kz,f            ;add uncounted tests
> quit6   incf    kz,f


quit5   skpnc
         goto   overflow

        movlw   -7 + 4  ;
        addwf   lo,f
        skpc
         decf   hi,f
        goto    quit1

quit4   incf    kz,f
        subwf   hi,f    ;counter-act the addwf

quit3   incf    kz,f
quit2
   ;subtract the 7 added in above - the incf's
   ;will keep track of how much needs to be added
   ;back. ignore the C, since the loop didn't get
   ;a chance to handle it.

        movlw   -7 + 1  ;+1 in lieu of incf kz,f
        addwf   lo,f

quit1   incf    kz,w

        addlw     CONSTANT      ;take into account
                                ;initial latency
>         addwf   lo,f
>         skpnc
>          incf   hi,f

        clrf    kz

>         return

overflow
        movlw   0xff
        movwf   lo
        movwf   hi
        clrf    kz
        return


I think that does it, but there's bound to be one or two cases I missed.

Scott