File content as of revision 1:6d557e90686e:

#include "mbed.h"
#include "InterruptIn.h"
#include "SoftPWM.h"

SoftPWM::SoftPWM(PinName _outpin,bool _positive) : pulse(_outpin)     //constructa  
{
    if ( _positive )
        pulse = 0;
    else
        pulse = 1;
    positive = _positive;
    interval = 0.005;
    width = 0;
    start(); 
}

float SoftPWM::read()
{
    if ( width <= 0.0 ) return 0.0;
    if ( width > 1.0 )  return 1.0;
    return width / interval;    
}

void SoftPWM::write(float duty)
{
    width = interval * duty;
    if ( duty <= 0.0 ) width =  0.0;
    if ( duty > 1.0 )  width =  interval;
}

void SoftPWM::start()
{
    _ticker.attach(this,&SoftPWM::TickerInterrapt,interval);
}

void SoftPWM::stop()
{
    _ticker.detach();
    if ( positive )
        pulse = 0;
    else
        pulse = 1;
    wait(width);
}

void SoftPWM::period(float _period)
{
    interval = _period;
    start();
}

void SoftPWM::period_ms(int _period)
{
    period((float)_period / 1000);
    start();
}

void SoftPWM::period_us(int _period)
{
    period((float)_period / 1000000);
    start();
}

void SoftPWM::pulsewidth(float _width)
{
    width = _width;
   if ( width < 0.0 ) width = 0.0;
}

void SoftPWM::pulsewidth_ms(int _width)
{
     pulsewidth((float)_width / 1000);
}

void SoftPWM::pulsewidth_us(int _width)
{
    pulsewidth((float)_width / 1000000);
}

void SoftPWM::TickerInterrapt()
{ 
    if ( width <= 0 ) return;
    _timeout.attach(this,&SoftPWM::end,width);
    if ( positive )
        pulse = 1;
    else
        pulse = 0;    
}

void SoftPWM::end()
{
    if ( positive )
        pulse = 0;
    else
        pulse = 1;    
    _timeout.detach();//原库中此句被注释掉 可能是作者认为此语句会占用cpu时间，但事实上注释掉后会在低占空比下消耗cpu时间并产生一些莫名其妙的问题
}
;