Servo.cpp

/*
 Servo.cpp - Interrupt driven Servo library for Arduino using 16 bit timers- Version 2
 Copyright (c) 2009 Michael Margolis.  All right reserved.
 
 This library 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 2.1 of the License, or (at your option) any later version.
 
 This library 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 this library; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

/* 
 
 A servo is activated by creating an instance of the Servo class passing the desired pin to the attach() method.
 The servos are pulsed in the background using the value most recently written using the write() method
 
 Note that analogWrite of PWM on pins associated with the timer are disabled when the first servo is attached.
 Timers are seized as needed in groups of 12 servos - 24 servos use two timers, 48 servos will use four.
 
 The methods are:
 
 Servo - Class for manipulating servo motors connected to Arduino pins.
 
 attach(pin )  - Attaches a servo motor to an i/o pin.
 attach(pin, min, max  ) - Attaches to a pin setting min and max values in microseconds
 default min is 544, max is 2400  
 
 write()     - Sets the servo angle in degrees.  (invalid angle that is valid as pulse in microseconds is treated as microseconds)
 writeMicroseconds() - Sets the servo pulse width in microseconds 
 read()      - Gets the last written servo pulse width as an angle between 0 and 180. 
 readMicroseconds()   - Gets the last written servo pulse width in microseconds. (was read_us() in first release)
 attached()  - Returns true if there is a servo attached. 
 detach()    - Stops an attached servos from pulsing its i/o pin. 
 
*/

#include <avr/interrupt.h>
#include "WProgram.h"


#include "Servo.h"

#define TICKS_PER_uS     (clockCyclesPerMicrosecond() / 8)  // number of timer ticks per microsecond with prescale of 8

#define SERVOS_PER_TIMER   12                               // the maximum number of servos controlled by one timer 
#define TRIM_DURATION     (SERVOS_PER_TIMER/2)              // compensation ticks to trim adjust for digitalWrite delays 

#define NBR_TIMERS        (MAX_SERVOS / SERVOS_PER_TIMER)

static servo_t servos[MAX_SERVOS];                         // static array of servo structures
static volatile int8_t Channel[NBR_TIMERS];                // counter for the servo being pulsed for each timer (or -1 if refresh interval)
#if defined(__AVR_ATmega1280__)
typedef enum { _timer5, _timer1, _timer3, _timer4 } servoTimer_t; // this is the sequence for timer utilization on mega
#else
typedef enum { _timer1 } servoTimer_t;                     // this is the sequence for timer utilization on other controllers 
#endif

uint8_t ServoCount = 0;                                     // the total number of attached servos

// convenience macros
#define SERVO_INDEX_TO_TIMER(_servo_nbr) ((servoTimer_t)(_servo_nbr / SERVOS_PER_TIMER)) // returns the timer controlling this servo
#define SERVO_INDEX_TO_CHANNEL(_servo_nbr) (_servo_nbr % SERVOS_PER_TIMER)       // returns the index of the servo on this timer
#define SERVO_INDEX(_timer,_channel)  ((_timer*SERVOS_PER_TIMER) + _channel)     // macro to access servo index by timer and channel
#define SERVO(_timer,_channel)  (servos[SERVO_INDEX(_timer,_channel)])            // macro to access servo class by timer and channel

#define SERVO_MIN() (MIN_PULSE_WIDTH - this->min * 4)  // minimum value in uS for this servo
#define SERVO_MAX() (MAX_PULSE_WIDTH - this->max * 4)  // maximum value in uS for this servo 

/************ static functions common to all instances ***********************/

static inline void handle_interrupts(servoTimer_t timer, volatile uint16_t *TCNTn, volatile uint16_t* OCRnA)
{
  if( Channel[timer] < 0 )
    *TCNTn = 0; // channel set to -1 indicated that refresh interval completed so reset the timer 
  else{
    if( SERVO_INDEX(timer,Channel[timer]) < ServoCount && SERVO(timer,Channel[timer]).Pin.isActive == true )  
      digitalWrite( SERVO(timer,Channel[timer]).Pin.nbr,LOW); // pulse this channel low if activated   
  }

  Channel[timer]++;    // increment to the next channel
  if( SERVO_INDEX(timer,Channel[timer]) < ServoCount && Channel[timer] < SERVOS_PER_TIMER) {
    *OCRnA = *TCNTn + SERVO(timer,Channel[timer]).ticks;
    if(SERVO(timer,Channel[timer]).Pin.isActive == true)     // check if activated
      digitalWrite( SERVO(timer,Channel[timer]).Pin.nbr,HIGH); // its an active channel so pulse it high   
  }  
  else { 
    // finished all channels so wait for the refresh period to expire before starting over 
    if( (unsigned)*TCNTn < (((unsigned int)REFRESH_INTERVAL * TICKS_PER_uS) + 4) )  // allow a few ticks to ensure the next OCR1A not missed
      *OCRnA = (unsigned int)REFRESH_INTERVAL * TICKS_PER_uS;  
    else 
      *OCRnA = *TCNTn + 4;  // at least REFRESH_INTERVAL has elapsed
    Channel[timer] = -1; // this will get incremented at the end of the refresh period to start again at the first channel
  }
}

SIGNAL (TIMER1_COMPA_vect) 
{ 
  handle_interrupts(_timer1, &TCNT1, &OCR1A); 
}

#if defined(__AVR_ATmega1280__)
SIGNAL (TIMER3_COMPA_vect) 
{ 
  handle_interrupts(_timer3, &TCNT3, &OCR3A); 
}
SIGNAL (TIMER4_COMPA_vect) 
{
  handle_interrupts(_timer4, &TCNT4, &OCR4A); 
}
SIGNAL (TIMER5_COMPA_vect) 
{
  handle_interrupts(_timer5, &TCNT5, &OCR5A); 
}
#endif

static void initISR(servoTimer_t timer)
{  
  if(timer == _timer1) {
    TCCR1A = 0;             // normal counting mode 
    TCCR1B = _BV(CS11);     // set prescaler of 8 
    TCNT1 = 0;              // clear the timer count 
#if defined(__AVR_ATmega8__)
    TIFR |= _BV(OCF1A);      // clear any pending interrupts; 
    TIMSK |=  _BV(OCIE1A) ;  // enable the output compare interrupt    
#else
    TIFR1 |= _BV(OCF1A);     // clear any pending interrupts; 
    TIMSK1 |=  _BV(OCIE1A) ; // enable the output compare interrupt 
#endif
  } 
#if defined(__AVR_ATmega1280__)
  else if(timer == _timer3) {
    TCCR3A = 0;             // normal counting mode 
    TCCR3B = _BV(CS31);     // set prescaler of 8  
    TCNT3 = 0;              // clear the timer count 
    TIFR3 = _BV(OCF3A);     // clear any pending interrupts; 
    TIMSK3 =  _BV(OCIE3A) ; // enable the output compare interrupt      
  }
  else if(timer == _timer4) {
    TCCR4A = 0;             // normal counting mode 
    TCCR4B = _BV(CS41);     // set prescaler of 8  
    TCNT4 = 0;              // clear the timer count 
    TIFR4 = _BV(OCF4A);     // clear any pending interrupts; 
    TIMSK4 =  _BV(OCIE4A) ; // enable the output compare interrupt      
  }
  else if(timer == _timer5) {
    TCCR5A = 0;             // normal counting mode 
    TCCR5B = _BV(CS51);     // set prescaler of 8  
    TCNT5 = 0;              // clear the timer count 
    TIFR5 = _BV(OCF5A);     // clear any pending interrupts; 
    TIMSK5 =  _BV(OCIE5A) ; // enable the output compare interrupt      
  }
#endif
} 

static boolean isTimerActive(servoTimer_t timer)
{
  // returns true if any servo is active on this timer
  for(uint8_t channel=0; channel < SERVOS_PER_TIMER; channel++) {
    if(SERVO(timer,channel).Pin.isActive == true)
      return true;
  }
  return false;
}


/****************** end of static functions ******************************/

Servo::Servo()
{
  if( ServoCount < MAX_SERVOS) {
    this->servoIndex = ServoCount++;                    // assign a servo index to this instance
    servos[this->servoIndex].ticks = DEFAULT_PULSE_WIDTH * TICKS_PER_uS;   // store default values  
  }
  else
    this->servoIndex = INVALID_SERVO ;  // too many servos 
}

uint8_t Servo::attach(int pin)
{
  return this->attach(pin, MIN_PULSE_WIDTH, MAX_PULSE_WIDTH);
}

uint8_t Servo::attach(int pin, int min, int max)
{
  if(this->servoIndex < MAX_SERVOS ) {
    pinMode( pin, OUTPUT) ;                                   // set servo pin to output
    servos[this->servoIndex].Pin.nbr = pin;  
    // todo min/max check: abs(min - MIN_PULSE_WIDTH) /4 < 128 
    this->min  = (MIN_PULSE_WIDTH - min)/4; //resolution of min/max is 4 uS
    this->max  = (MAX_PULSE_WIDTH - max)/4; 
    // initialize the timer if it has not already been initialized 
    servoTimer_t timer = SERVO_INDEX_TO_TIMER(servoIndex);
    if(isTimerActive(timer) == false)
      initISR(timer);    
    servos[this->servoIndex].Pin.isActive = true;  // this must be set after the check for isTimerActive
  } 
  return this->servoIndex ;
}

void Servo::detach()  
{
  servos[this->servoIndex].Pin.isActive = false;  

#ifdef FREE_TIMERS
  if(isTimerActive(SERVO_INDEX_TO_TIMER(servoIndex)) == false) {
    ;// call to unimplimented function in wiring.c to re-init timer (set timer back to PWM mode) TODO? 
  }
#endif
}

void Servo::write(int value)
{  
  if(value < MIN_PULSE_WIDTH)
  {  // treat values less than 544 as angles in degrees (valid values in microseconds are handled as microseconds)
    if(value < 0) value = 0;
    if(value > 180) value = 180;
    value = map(value, 0, 180, SERVO_MIN(),  SERVO_MAX());      
  }
  this->writeMicroseconds(value);
}

void Servo::writeMicroseconds(int value)
{
  // calculate and store the values for the given channel
  byte channel = this->servoIndex;
  if( (channel >= 0) && (channel < MAX_SERVOS) )   // ensure channel is valid
  {  
    if( value < SERVO_MIN() )          // ensure pulse width is valid
      value = SERVO_MIN();
    else if( value > SERVO_MAX() )
      value = SERVO_MAX();   
    
    value = (value-TRIM_DURATION) * TICKS_PER_uS;  // convert to ticks after compensating for interrupt overhead
    uint8_t oldSREG = SREG;
    cli();
    servos[channel].ticks = value;  
    SREG = oldSREG;   
  } 
}

int Servo::read() // return the value as degrees
{
  return  map( this->readMicroseconds()+1, SERVO_MIN(), SERVO_MAX(), 0, 180);     
}

int Servo::readMicroseconds()
{
  unsigned int pulsewidth;
  if( this->servoIndex != INVALID_SERVO )
    pulsewidth = (servos[this->servoIndex].ticks /  TICKS_PER_uS) + TRIM_DURATION ;
  else 
    pulsewidth  = 0;

  return pulsewidth;   
}

bool Servo::attached()
{
  return servos[this->servoIndex].Pin.isActive ;
}