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/*
* softPwm.c:
* Provide many channels of software driven PWM.
* Copyright (c) 2012-2017 Gordon Henderson
***********************************************************************
* This file is part of wiringPi:
* https://projects.drogon.net/raspberry-pi/wiringpi/
*
* wiringPi is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* wiringPi is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with wiringPi.
* If not, see <http://www.gnu.org/licenses/>.
***********************************************************************
*/
#include <stdio.h>
#include <malloc.h>
#include <pthread.h>
#include "wiringPi.h"
#include "softPwm.h"
// MAX_PINS:
// This is more than the number of Pi pins because we can actually softPwm.
// Once upon a time I let pins on gpio expanders be softPwm'd, but it's really
// really not a good thing.
#define MAX_PINS 64
// The PWM Frequency is derived from the "pulse time" below. Essentially,
// the frequency is a function of the range and this pulse time.
// The total period will be range * pulse time in µS, so a pulse time
// of 100 and a range of 100 gives a period of 100 * 100 = 10,000 µS
// which is a frequency of 100Hz.
//
// It's possible to get a higher frequency by lowering the pulse time,
// however CPU uage will skyrocket as wiringPi uses a hard-loop to time
// periods under 100µS - this is because the Linux timer calls are just
// not accurate at all, and have an overhead.
//
// Another way to increase the frequency is to reduce the range - however
// that reduces the overall output accuracy...
#define PULSE_TIME 100
static volatile int marks [MAX_PINS] ;
static volatile int range [MAX_PINS] ;
static volatile pthread_t threads [MAX_PINS] ;
static volatile int newPin = -1 ;
/*
* softPwmThread:
* Thread to do the actual PWM output
*********************************************************************************
*/
static void *softPwmThread (void *arg)
{
int pin, mark, space ;
struct sched_param param ;
param.sched_priority = sched_get_priority_max (SCHED_RR) ;
pthread_setschedparam (pthread_self (), SCHED_RR, &param) ;
pin = *((int *)arg) ;
free (arg) ;
pin = newPin ;
newPin = -1 ;
piHiPri (90) ;
for (;;)
{
mark = marks [pin] ;
space = range [pin] - mark ;
if (mark != 0)
digitalWrite (pin, HIGH) ;
delayMicroseconds (mark * 100) ;
if (space != 0)
digitalWrite (pin, LOW) ;
delayMicroseconds (space * 100) ;
}
return NULL ;
}
/*
* softPwmWrite:
* Write a PWM value to the given pin
*********************************************************************************
*/
void softPwmWrite (int pin, int value)
{
if (pin < MAX_PINS)
{
/**/ if (value < 0)
value = 0 ;
else if (value > range [pin])
value = range [pin] ;
marks [pin] = value ;
}
}
/*
* softPwmCreate:
* Create a new softPWM thread.
*********************************************************************************
*/
int softPwmCreate (int pin, int initialValue, int pwmRange)
{
int res ;
pthread_t myThread ;
int *passPin ;
if (pin >= MAX_PINS)
return -1 ;
if (range [pin] != 0) // Already running on this pin
return -1 ;
if (pwmRange <= 0)
return -1 ;
passPin = malloc (sizeof (*passPin)) ;
if (passPin == NULL)
return -1 ;
digitalWrite (pin, LOW) ;
pinMode (pin, OUTPUT) ;
marks [pin] = initialValue ;
range [pin] = pwmRange ;
*passPin = pin ;
newPin = pin ;
res = pthread_create (&myThread, NULL, softPwmThread, (void *)passPin) ;
while (newPin != -1)
delay (1) ;
threads [pin] = myThread ;
return res ;
}
/*
* softPwmStop:
* Stop an existing softPWM thread
*********************************************************************************
*/
void softPwmStop (int pin)
{
if (pin < MAX_PINS)
{
if (range [pin] != 0)
{
pthread_cancel (threads [pin]) ;
pthread_join (threads [pin], NULL) ;
range [pin] = 0 ;
digitalWrite (pin, LOW) ;
}
}
}