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+/*
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+ * softPwm.c:
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+ * Provide 2 channels of software driven PWM.
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+ * Copyright (c) 2012 Gordon Henderson
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+ ***********************************************************************
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+ * This file is part of wiringPi:
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+ * https://projects.drogon.net/raspberry-pi/wiringpi/
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+ *
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+ * wiringPi is free software: you can redistribute it and/or modify
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+ * it under the terms of the GNU Lesser General Public License as
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+ * published by the Free Software Foundation, either version 3 of the
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+ * License, or (at your option) any later version.
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+ *
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+ * wiringPi is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ * GNU Lesser General Public License for more details.
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+ *
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+ * You should have received a copy of the GNU Lesser General Public
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+ * License along with wiringPi.
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+ * If not, see <http://www.gnu.org/licenses/>.
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+ ***********************************************************************
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+ */
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+
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+#include <stdio.h>
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+#include <pthread.h>
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+
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+#include "wiringPi.h"
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+#include "softPwm.h"
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+
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+#define MAX_PINS 64
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+
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+// The PWM Frequency is derived from the "pulse time" below. Essentially,
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+// the frequency is a function of the range and this pulse time.
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+// The total period will be range * pulse time in uS, so a pulse time
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+// of 100 and a range of 100 gives a period of 100 * 100 = 10,000 uS
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+// which is a frequency of 100Hz.
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+//
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+// It's possible to get a higher frequency by lowering the pulse time,
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+// however CPU uage will skyrocket as wiringPi uses a hard-loop to time
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+// periods under 100uS - this is because the Linux timer calls are just
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+// accurate at all, and have an overhead.
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+//
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+// Another way to increase the frequency is to reduce the range - however
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+// that reduces the overall output accuracy...
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+
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+#define PULSE_TIME 100
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+
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+static int marks [MAX_PINS] ;
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+static int range [MAX_PINS] ;
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+
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+int newPin = -1 ;
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+
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+
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+/*
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+ * softPwmThread:
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+ * Thread to do the actual PWM output
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+ *********************************************************************************
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+ */
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+
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+static PI_THREAD (softPwmThread)
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+{
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+ int pin, mark, space ;
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+
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+ pin = newPin ;
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+ newPin = -1 ;
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+
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+ piHiPri (50) ;
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+
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+ for (;;)
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+ {
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+ mark = marks [pin] ;
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+ space = range [pin] - mark ;
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+
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+ if (mark != 0)
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+ digitalWrite (pin, HIGH) ;
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+ delayMicroseconds (mark * 100) ;
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+
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+ if (space != 0)
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+ digitalWrite (pin, LOW) ;
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+ delayMicroseconds (space * 100) ;
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+ }
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+
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+ return NULL ;
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+}
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+
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+void softPwmWrite (int pin, int value)
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+{
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+ marks [pin] = value ;
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+}
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+
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+
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+/*
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+ * softPwmCreate:
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+ * Create a new PWM thread.
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+ *********************************************************************************
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+ */
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+
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+int softPwmCreate (int pin, int initialValue, int pwmRange)
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+{
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+ int res ;
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+
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+ pinMode (pin, OUTPUT) ;
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+ digitalWrite (pin, LOW) ;
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+
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+ marks [pin] = initialValue ;
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+ range [pin] = pwmRange ;
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+
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+ newPin = pin ;
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+ res = piThreadCreate (softPwmThread) ;
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+
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+ while (newPin != -1)
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+ delay (1) ;
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+
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+ return res ;
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+}
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