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/pwmsw.c

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/*! \file pwmsw.c \brief Software interrupt-driven multi-output PWM function library. */
//*****************************************************************************
//
// File Name    : 'pwmsw.c'
// Title        : Software interrupt-driven multi-output PWM function library
// Author       : Pascal Stang - Copyright (C) 2002
// Created      : 7/20/2002
// Revised      : 7/31/2002
// Version      : 0.1
// Target MCU   : Atmel AVR Series
// Editor Tabs  : 4
//
// This code is distributed under the GNU Public License
//      which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************

#ifndef WIN32
    #include <avr/io.h>
#endif

#include "global.h"
#include "pwmsw.h"

// Program ROM constants

// Global variables
// PWM channel registers
u16 PosTics;
u16 PeriodTics;
u08 Channel;
SwPwmChannelType SwPwmChannels[SWPWM_NUM_CHANNELS];

// functions

// initializes software PWM system
void pwmswInit(u16 periodTics)
{
    u08 index;

    // attach the software PWM service routine to timer1 output compare A
    timerAttach(TIMER1OUTCOMPAREA_INT, pwmswService);
    // set PeriodTics
    PeriodTics = periodTics;
    // set PosTics
    PosTics = 0;
    // clear channels
    for(index=0; index<SWPWM_NUM_CHANNELS; index++)
    {
        SwPwmChannels[index].duty = 0;
        SwPwmChannels[index].setduty = 0;
    }
    // set initial interrupt time
    u16 OCValue;
    // read in current value of output compare register OCR1A
    OCValue =  inb(OCR1AL);     // read low byte of OCR1A
    OCValue += inb(OCR1AH)<<8;  // read high byte of OCR1A
    // increment OCR1A value by nextTics
    OCValue += PeriodTics; 
    // set future output compare time to this new value
    outb(OCR1AH, (OCValue>>8));         // write high byte
    outb(OCR1AL, (OCValue & 0x00FF));   // write low byte

    // enable the timer1 output compare A interrupt
    sbi(TIMSK, OCIE1A);
}

// turns off software PWM system
void pwmswOff(void)
{
    // disable the timer1 output compare A interrupt
    cbi(TIMSK, OCIE1A);
    // detach the service routine
    timerDetach(TIMER1OUTCOMPAREA_INT);
}

// set duty on channel
void pwmswPWMSet(u08 channel, u16 duty)
{
    // compare with max value of PeriodTics
    duty = MIN(duty, PeriodTics);
    SwPwmChannels[channel].setduty = duty;
}

void pwmswService(void)
{
    u16 nextTics=PeriodTics;
    u08 index;

    // check for beginning of period
    if(PosTics == 0)
    {
        // examine all channels
        for(index=0; index<SWPWM_NUM_CHANNELS; index++)
        {
            // transfer set-duty to active-duty
            SwPwmChannels[index].duty = SwPwmChannels[index].setduty;
            // find next channel event to schedule
            //      if no channel has a duty setting greater than 0 (PosTics);
            //      nextTics will remain at PeriodTics for the next cycle
            if(SwPwmChannels[index].duty)
            {
                nextTics = MIN(nextTics, SwPwmChannels[index].duty);
                // set all non-zero channels to on
                outb(SWPWMPORT, inb(SWPWMPORT) | (1<<index));
            }
        }
    }
    else
    {
        // examine all channels
        for(index=0; index<SWPWM_NUM_CHANNELS; index++)
        {
            // check if we have a duty cycle match
            if(PosTics == SwPwmChannels[index].duty)
            {
                // clear output channel
                outb(SWPWMPORT, inb(SWPWMPORT) & ~(1<<index));
            }
            // find next channel event to schedule
            //      if no channel has a duty setting greater than PosTics;
            //      nextTics will remain at PeriodTics and is handled below
            if(SwPwmChannels[index].duty > PosTics)
                nextTics = MIN(nextTics, SwPwmChannels[index].duty-PosTics);
        }
        if(nextTics == PeriodTics)
        {
            // no more channels to schedule
            // schedule next cycle
            nextTics = PeriodTics - PosTics;
        }
    }

    // schedule next interrupt
    u16 OCValue;
    // read in current value of output compare register OCR1A
    OCValue =  inb(OCR1AL);     // read low byte of OCR1A
    OCValue += inb(OCR1AH)<<8;  // read high byte of OCR1A
    // increment OCR1A value by nextTics
    OCValue += nextTics;
//  OCR1A+=nextTics;
    // set future output compare time to this new value
    outb(OCR1AH, (OCValue>>8));         // write high byte
    outb(OCR1AL, (OCValue & 0x00FF));   // write low byte
    // set our new tic position
    PosTics += nextTics;
    if(PosTics >= PeriodTics) PosTics -= PeriodTics;
}

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