8/20/02 12:36:50 PM, Roman Black <fastvid@EZY.NET.AU> wrote:

>So if anyone feels like a quickie challenge,
>can this 15 cycle code be reduced to 12 cycle code
>AND satisfy these:
>* must be 8/4 cycles PWM.
>* must have minimum 1 inst between write and read.

If we can assume that the inputs variable is only accessed outside the loop (i.e. *not* by any
interrupt handler that could be activated during the loop):

>pwm_loop
>                                ; first output current1 to motor
>        movf current1,w         ; get currents and phase switching
>        movwf PORTB             ; send to motor!
>
>        nop                     ;
>        nop                     ;
>        nop                     ; (5 cycles)

Drop that last nop.

>
>        ;-------------------------
>                                ; now output current2
>        movf current2,w         ;
>        movwf PORTB             ; send to motor!
>
>        nop                     ; let ports settle
>        nop                     ; + some delay

Drop that last nop.

>                                ; now test input pins
>        movf PORTA,w            ; get pin values from port
>        movwf inputs            ; store in var

Drop the movwf
>
>        xorwf inputs_last,w     ; xor to compare new inputs with last values
>        skpnz
>        goto pwm_loop           ; z, inputs not changed, so keep looping
>                                ; (10 cycles)
>        ;-------------------------------------------------

And add (now we're outside the loop):

 xorwf inputs_last,w
 movwf inputs

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