+/*
+ * softPwm.c:
+ * Provide 2 channels of software driven PWM.
+ * Copyright (c) 2012 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 <pthread.h>
+
+#include "wiringPi.h"
+#include "softPwm.h"
+
+#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 uS, so a pulse time
+// of 100 and a range of 100 gives a period of 100 * 100 = 10,000 uS
+// 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 100uS - this is because the Linux timer calls are just
+// 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 int marks [MAX_PINS] ;
+static int range [MAX_PINS] ;
+
+int newPin = -1 ;
+
+
+/*
+ * softPwmThread:
+ * Thread to do the actual PWM output
+ *********************************************************************************
+ */
+
+static PI_THREAD (softPwmThread)
+{
+ int pin, mark, space ;
+
+ pin = newPin ;
+ newPin = -1 ;
+
+ piHiPri (50) ;
+
+ 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 ;
+}
+
+void softPwmWrite (int pin, int value)
+{
+ marks [pin] = value ;
+}
+
+
+/*
+ * softPwmCreate:
+ * Create a new PWM thread.
+ *********************************************************************************
+ */
+
+int softPwmCreate (int pin, int initialValue, int pwmRange)
+{
+ int res ;
+
+ pinMode (pin, OUTPUT) ;
+ digitalWrite (pin, LOW) ;
+
+ marks [pin] = initialValue ;
+ range [pin] = pwmRange ;
+
+ newPin = pin ;
+ res = piThreadCreate (softPwmThread) ;
+
+ while (newPin != -1)
+ delay (1) ;
+
+ return res ;
+}