Hi assembler code gurus, I have a short piece of
asm for high speed PWM code, that currently takes
15 cycles. Preferably I would like it to be 12 cycles.
:o)

The PWM code must divide by 3, doing 2/3 the time
at Current 2, and 1/3 of the time at current 1.

At the moment it is 15 cycles total, 267 kHz.
I would like 12 cycles, 333 kHz.

This has been stumping me for an hour now, most
annoying. My problem is that I need to check for
any change in inputs on PORTA at some point during
the 12 cycles. The only solutions I have require
reading PORTA directly after writing PORTB, which
I don't like as it is only 62nS between the two
and i'm moving 100+ mA out PORTB...

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.
:o)
-Roman


        ;-------------------------------------------------
        ; PWM LOOP
        ; (the 2 target currents were set previously)

        ; what this function does is spend 2 time units at current2,
        ; and 1 time unit at current1.
        ; actual is 10 cycles at current2
        ; and 5 cycles at current 1

        ; this gives an average pwm current of 2/3 the way between
        ; current2 and current1.

        ; pwm frequency is 267 kHz. (16MHz resonator)

        ; also checks for any change in input pins in this 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)

        ;-------------------------
                                ; now output current2
        movf current2,w         ;
        movwf PORTB             ; send to motor!

        nop                     ; let ports settle
        nop                     ; + some delay

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

        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)
        ;-------------------------------------------------

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