> From: Sam Linder <SamLKILLspamIN-INC.COM>
> To: .....PICLISTKILLspam.....MITVMA.MIT.EDU
> Subject: [PIC]: usec delay routine
> Date: Thursday, September 07, 2000 18:03
>
> Does anyone have a simple, yet accurate software usec delay routine?
> I'm running 4mhz PIC16F877 and want to be able to generate a call to
> SoftUsecDelay(NumberOfMicrosecondsToDelay).
>
> I've looked at some delay routines (such as PICLOOPS) but they aren't
> accurate down to the usec level and don't seem to allow for a call
> containing the desired number of microseconds.
>
> Any suggestions out there?
>
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> >From a message I posted two years ago (and which I just found, in
> about 5 seconds, searching the PICLIST archive at http://www.piclist.com for
> the word "delay"):
>
>     Try this; it generates delays with a resolution of one cycle,
>     although it's limited to the range [20-271].
>
>         MOVLW   X
>         CALL    DELAY
>
>         ....
>
>     ; This routine delays X cycles.  Enter with X (in the range
>     ; [20-271]) in the W register.
>     ;
>     ; Note that the delay is inclusive of the "MOVLW X", "CALL
>     ; DELAY", and "RETURN" overhead, so a sequence like:
>     ;
>     ;     MOVLW   100
>     ;     CALL    DELAY
>     ;     MOVLW   200
>     ;     CALL    DELAY
>     ;
>     ; will delay EXACTLY 300 cycles.
>
>     DELAY:
>
>         MOVWF   COUNTER
>
>         BTFSC   COUNTER, 0
>         GOTO    $+1
>
>         BTFSS   COUNTER, 1
>         GOTO    SKIP
>         NOP
>         GOTO    $+1
>
>     SKIP:
>
>         RRF     COUNTER
>         RRF     COUNTER
>
>         MOVLW   4
>         SUBWF   COUNTER
>
>         BCF     COUNTER,6
>         BCF     COUNTER,7
>
>     LOOP:
>
>         NOP
>         DECFSZ  COUNTER
>         GOTO    LOOP
>
>         RETURN

> ;10 bit delay routine providing 1 cycle resolution.  Works with both 12 &
> 14 bit core PICs.
> ;Original idea from Mike Harrison.  This version by Dwayne Reid
> ;
> ;enters with upper 8 bits of delay in DELAYU, lower 2 bits in bits 1,0 of
> DELAYL
> ;bits 7..2 in DELAYL can be used as flags for whatever purpose desired.
> ;returns with W destroyed
> Delay10bit      ;delay is 10 bit value + 7 cycles ( + call + return, if any)
>      incf        DELAYU,F        ;correct for dec & test instead of test & dec
> Dly10bLoop
>      comf        DELAYL,W        ;invert LSBs
>      decfsz      DELAYU,F
>        goto      Dly10bLoop      ;coarse delay to closest 4 cycles
>      andlw       b'00000011'
>      addwf       PCL,F
>      nop
>      nop
>      nop

> I hope one of these is useful.

> dwayne

> unsigned char delayU, delayL;   // C code
> #asm
> Delay10bit              // delay is 10 bit value + 7 cycles ( + call +
> return, if any)
>     incf    _delayU,f   // correct for dec & test instead of test & dec
> Dly10bLoop:
>     comf    _delayL,w   // invert LSBs
>     decfsz  _delayU,f
>     goto    Dly10bLoop  // coarse delay to closest 4 cycles
>     andlw   3
>
>     // this additional code checks for the
>     // page boundary and sets pclath correctly
>     // ****
>     movwf   _delayL
>     movlw   low offset
>     addwf   _delayL
>     movlw   high offset
>     btfsc   status,C
>     addlw   1
>     movwf   pclath
>     movf    _delayL,w
>     // ****
>
>     addwf   pcl,f
> offset:
>     nop
>     nop
>     nop
>     return
> #endasm

> unsigned char delayU, delayL;   // C code
> #asm
> Delay10bit              // delay is 10 bit value + 7 cycles ( + call +
> return, if any)
>     incf    _delayU,f   // correct for dec & test instead of test & dec
> Dly10bLoop:
>     comf    _delayL,w   // invert LSBs
>     decfsz  _delayU,f
>     goto    Dly10bLoop  // coarse delay to closest 4 cycles
>     andlw   3

> unsigned char delayU, delayL;   // C code
> #asm
> Delay10bit              // delay is 10 bit value + 7 cycles ( + call +
> return, if any)
>     incf    _delayU,f   // correct for dec & test instead of test & dec
> Dly10bLoop:
>     comf    _delayL,w   // invert LSBs
>     decfsz  _delayU,f
>     goto    Dly10bLoop  // coarse delay to closest 4 cycles
>     andlw   3
>
>     // this additional code checks for the
>     // page boundary and sets pclath correctly
>     // ****
>     movwf   _delayL
>     movlw   low offset
>     addwf   _delayL
>     movlw   high offset
>     btfsc   status,C
>     addlw   1
>     movwf   pclath
>     movf    _delayL,w
>     // ****
>
>     addwf   pcl,f
> offset:
>     nop
>     nop
>     nop
>     return
> #endasm

> unsigned char delayU, delayL;   // C code
> #asm
> Delay10bit              // delay is 10 bit value + 7 cycles ( + call +
> return, if any)
>     incf    _delayU,f   // correct for dec & test instead of test & dec
> Dly10bLoop:
>     comf    _delayL,w   // invert LSBs
>     decfsz  _delayU,f
>     goto    Dly10bLoop  // coarse delay to closest 4 cycles
>     andlw   3

> Scott:
> <snip>
> It's little more efficient to do this:
>
>       addlw   offset
>       skpnc
>       incf   pclath,f
>
>       movwf   pcl
> offset:<snip>
>
> While interesting, your code suggestion doesn't work in my particular
> environment. When I compile with Hi-Tech C, I get the following error
> messages during the link. They are directly related to "addlw  offset":
>
> Error[000] comomain.obj 249 : Fixup overflow in expression (loc 0x12CC
> (0x12CC+0), size 1, value 0x969)
> Error[000] comomain.rlf 6236 : Fixup overflow in expression (loc 0x76
> (0x76+0), size 1, value 0x969)
>
> As if that weren't enough, the compiler simply ignores "skpnc" - it