/*
* softServo.c:
* Provide N channels of software driven PWM suitable for RC
* servo motors.
* 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 <string.h>
#include <time.h>
#include <sys/time.h>
#include <pthread.h>
#include "wiringPi.h"
#include "softServo.h"
// RC Servo motors are a bit of an oddity - designed in the days when
// radio control was experimental and people were tryin to make
// things as simple as possible as it was all very expensive...
//
// So... To drive an RC Servo motor, you need to send it a modified PWM
// signal - it needs anything from 1ms to 2ms - with 1ms meaning
// to move the server fully left, and 2ms meaning to move it fully
// right. Then you need a long gap before sending the next pulse.
// The reason for this is that you send a multiplexed stream of these
// pulses up the radio signal into the reciever which de-multiplexes
// them into the signals for each individual servo. Typically there
// might be 8 channels, so you need at least 8 "slots" of 2mS pulses
// meaning the entire frame must fit into a 16mS slot - which would
// then be repeated...
//
// In practice we have a total slot width of about 20mS - so we're sending 50
// updates per second to each servo.
//
// In this code, we don't need to be too fussy about the gap as we're not doing
// the multipexing, but it does need to be at least 10mS, and preferably 16
// from what I've been able to determine.
// WARNING:
// This code is really experimental. It was written in response to some people
// asking for a servo driver, however while it works, there is too much
// jitter to successfully drive a small servo - I have tried it with a micro
// servo and it worked, but the servo ran hot due to the jitter in the signal
// being sent to it.
//
// If you want servo control for the Pi, then use the servoblaster kernel
// module.
#define MAX_SERVOS 8
static int pinMap [MAX_SERVOS] ; // Keep track of our pins
static int pulseWidth [MAX_SERVOS] ; // microseconds
/*
* softServoThread:
* Thread to do the actual Servo PWM output
*********************************************************************************
*/
static PI_THREAD (softServoThread)
{
register int i, j, k, m, tmp ;
int lastDelay, pin, servo ;
int myDelays [MAX_SERVOS] ;
int myPins [MAX_SERVOS] ;
struct timeval tNow, tStart, tPeriod, tGap, tTotal ;
struct timespec tNs ;
tTotal.tv_sec = 0 ;
tTotal.tv_usec = 8000 ;
piHiPri (50) ;
for (;;)
{
gettimeofday (&tStart, NULL) ;
memcpy (myDelays, pulseWidth, sizeof (myDelays)) ;
memcpy (myPins, pinMap, sizeof (myPins)) ;
// Sort the delays (& pins), shortest first
for (m = MAX_SERVOS / 2 ; m > 0 ; m /= 2 )
for (j = m ; j < MAX_SERVOS ; ++j)
for (i = j - m ; i >= 0 ; i -= m)
{
k = i + m ;
if (myDelays [k] >= myDelays [i])
break ;
else // Swap
{
tmp = myDelays [i] ; myDelays [i] = myDelays [k] ; myDelays [k] = tmp ;
tmp = myPins [i] ; myPins [i] = myPins [k] ; myPins [k] = tmp ;
}
}
// All on
lastDelay = 0 ;
for (servo = 0 ; servo < MAX_SERVOS ; ++servo)
{
if ((pin = myPins [servo]) == -1)
continue ;
digitalWrite (pin, HIGH) ;
myDelays [servo] = myDelays [servo] - lastDelay ;
lastDelay += myDelays [servo] ;
}
// Now loop, turning them all off as required
for (servo = 0 ; servo < MAX_SERVOS ; ++servo)
{
if ((pin = myPins [servo]) == -1)
continue ;
delayMicroseconds (myDelays [servo]) ;
digitalWrite (pin, LOW) ;
}
// Wait until the end of an 8mS time-slot
gettimeofday (&tNow, NULL) ;
timersub (&tNow, &tStart, &tPeriod) ;
timersub (&tTotal, &tPeriod, &tGap) ;
tNs.tv_sec = tGap.tv_sec ;
tNs.tv_nsec = tGap.tv_usec * 1000 ;
nanosleep (&tNs, NULL) ;
}
return NULL ;
}
/*
* softServoWrite:
* Write a Servo value to the given pin
*********************************************************************************
*/
void softServoWrite (int servoPin, int value)
{
int servo ;
servoPin &= 63 ;
/**/ if (value < -250)
value = -250 ;
else if (value > 1250)
value = 1250 ;
for (servo = 0 ; servo < MAX_SERVOS ; ++servo)
if (pinMap [servo] == servoPin)
pulseWidth [servo] = value + 1000 ; // uS
}
/*
* softServoSetup:
* Setup the software servo system
*********************************************************************************
*/
int softServoSetup (int p0, int p1, int p2, int p3, int p4, int p5, int p6, int p7)
{
int servo ;
if (p0 != -1) { pinMode (p0, OUTPUT) ; digitalWrite (p0, LOW) ; }
if (p1 != -1) { pinMode (p1, OUTPUT) ; digitalWrite (p1, LOW) ; }
if (p2 != -1) { pinMode (p2, OUTPUT) ; digitalWrite (p2, LOW) ; }
if (p3 != -1) { pinMode (p3, OUTPUT) ; digitalWrite (p3, LOW) ; }
if (p4 != -1) { pinMode (p4, OUTPUT) ; digitalWrite (p4, LOW) ; }
if (p5 != -1) { pinMode (p5, OUTPUT) ; digitalWrite (p5, LOW) ; }
if (p6 != -1) { pinMode (p6, OUTPUT) ; digitalWrite (p6, LOW) ; }
if (p7 != -1) { pinMode (p7, OUTPUT) ; digitalWrite (p7, LOW) ; }
pinMap [0] = p0 ;
pinMap [1] = p1 ;
pinMap [2] = p2 ;
pinMap [3] = p3 ;
pinMap [4] = p4 ;
pinMap [5] = p5 ;
pinMap [6] = p6 ;
pinMap [7] = p7 ;
for (servo = 0 ; servo < MAX_SERVOS ; ++servo)
pulseWidth [servo] = 1500 ; // Mid point
return piThreadCreate (softServoThread) ;
}