holy-shit-who-reads-this.cpp

/* ServoTimer2.cpp*/
extern "C" {
  // AVR LibC Includes
  #include <inttypes.h>
  #include <avr/interrupt.h>
  #include "WConstants.h"
}
#include <wiring.h>
#include "ServoTimer2.h"
static void initISR();   
static void writeChan(uint8_t chan, int pulsewidth);

#define FRAME_SYNC_INDEX   0             // frame sync delay is the first entry in the channel array
#define FRAME_SYNC_PERIOD  20000         // total frame duration in microseconds 
#define FRAME_SYNC_DELAY   ((FRAME_SYNC_PERIOD - ( NBR_CHANNELS * DEFAULT_PULSE_WIDTH))/ 128) // number of iterations of the ISR to get the desired frame rate
#define DELAY_ADJUST       8             // number of microseconds of calculation overhead to be subtracted from pulse timings   

static servo_t servos[NBR_CHANNELS+1];    // static array holding servo data for all channels

static volatile uint8_t Channel;   // counter holding the channel being pulsed
static volatile uint8_t ISRCount;  // iteration counter used in the interrupt routines;
uint8_t ChannelCount = 0;          // counter holding the number of attached channels
static boolean isStarted = false;  // flag to indicate if the ISR has been initialised

ISR (TIMER2_OVF_vect)
{ 
  ++ISRCount; // increment the overlflow counter
  if (ISRCount ==  servos[Channel].counter ) // are we on the final iteration for this channel
  {
      TCNT2 =  servos[Channel].remainder;   // yes, set count for overflow after remainder ticks
  }  
  else if(ISRCount >  servos[Channel].counter)  
  {
      // we have finished timing the channel so pulse it low and move on
      if(servos[Channel].Pin.isActive == true)           // check if activated
          digitalWrite( servos[Channel].Pin.nbr,LOW); // pulse this channel low if active   

        Channel++;    // increment to the next channel
      ISRCount = 0; // reset the isr iteration counter 
      TCNT2 = 0;    // reset the clock counter register
      if( (Channel != FRAME_SYNC_INDEX) && (Channel <= NBR_CHANNELS) ){           // check if we need to pulse this channel    
          if(servos[Channel].Pin.isActive == true)         // check if activated
             digitalWrite( servos[Channel].Pin.nbr,HIGH); // its an active channel so pulse it high   
      }
      else if(Channel > NBR_CHANNELS){ 
         Channel = 0; // all done so start over               
      } 
   }  
}

ServoTimer2::ServoTimer2()
{
   if( ChannelCount < NBR_CHANNELS)  
      this->chanIndex = ++ChannelCount;  // assign a channel number to this instance
   else
      this->chanIndex = 0;  // todo      // too many channels, assigning 0 inhibits this instance from functioning 

uint8_t ServoTimer2::attach(int pin)
{
      if( isStarted == false)
       initISR();    
      if(this->chanIndex > 0)  
      {
       //debug("attaching chan = ", chanIndex);
       pinMode( pin, OUTPUT) ;  // set servo pin to output
       servos[this->chanIndex].Pin.nbr = pin;  
       servos[this->chanIndex].Pin.isActive = true;  
      } 
      return this->chanIndex ;
}

void ServoTimer2::detach()  
{
    servos[this->chanIndex].Pin.isActive = false;  
}

void ServoTimer2::write(int pulsewidth)
{      
   writeChan(this->chanIndex, pulsewidth); // call the static function to store the data for this servo          
}

int ServoTimer2::read()
{
  unsigned int pulsewidth;
   if( this->chanIndex > 0)
      pulsewidth =  servos[this->chanIndex].counter * 128 + ((255 - servos[this->chanIndex].remainder) / 2) + DELAY_ADJUST ;
   else 
       pulsewidth  = 0;
   return pulsewidth;   
}
 
boolean ServoTimer2::attached()
{
    return servos[this->chanIndex].Pin.isActive ;
}

static void writeChan(uint8_t chan, int pulsewidth)
{
   // calculate and store the values for the given channel
   if( (chan > 0) && (chan <= NBR_CHANNELS) )   // ensure channel is valid
   { 
      if( pulsewidth < MIN_PULSE_WIDTH )                // ensure pulse width is valid
          pulsewidth = MIN_PULSE_WIDTH;
      else if( pulsewidth > MAX_PULSE_WIDTH )
          pulsewidth = MAX_PULSE_WIDTH;       
      
        pulsewidth -=DELAY_ADJUST;                   // subtract the time it takes to process the start and end pulses (mostly from digitalWrite) 
      servos[chan].counter = pulsewidth / 128;      
      servos[chan].remainder = 255 - (2 * (pulsewidth - ( servos[chan].counter * 128)));  // the number of 0.5us ticks for timer overflow         
   }
}

static void initISR()
{   
      for(uint8_t i=1; i <= NBR_CHANNELS; i++) {  // channels start from 1    
         writeChan(i, DEFAULT_PULSE_WIDTH);  // store default values          
      }
      servos[FRAME_SYNC_INDEX].counter = FRAME_SYNC_DELAY;   // store the frame sync period       

      Channel = 0;  // clear the channel index  
      ISRCount = 0;  // clear the value of the ISR counter;
      
      /* setup for timer 2 */
      TIMSK2 = 0;  // disable interrupts 
      TCCR2A = 0;  // normal counting mode 
      TCCR2B = _BV(CS21); // set prescaler of 8 
      TCNT2 = 0;     // clear the timer2 count 
      TIFR2 = _BV(TOV2);  // clear pending interrupts; 
      TIMSK2 =  _BV(TOIE2) ; // enable the overflow interrupt        
        
      isStarted = true;  // flag to indicate this initialisation code has been executed
}

this-looks-awful.cpp

/*
  ServoTimer2.h - Interrupt driven Servo library for Arduino using 
/* 
  This library uses Timer2 to drive up to 8 servos using interrupts so no refresh activity is required from within the sketch. 
  The usage and method naming is similar to the Arduino software servo library http://www.arduino.cc/playground/ComponentLib/Servo
  except that pulse widths are in microseconds.
 
  
  A servo is activated by creating an instance of the Servo class passing the desired pin to the attach() method.
  The servo is pulsed in the background to the value most recently written using the write() method

  Note that analogWrite of PWM on pins 3 and 11 is disabled when the first servo is attached

  The methods are:

   ServoTimer2 - 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 pulse width in microseconds.

   read()      - Gets the last written servo pulse width in microseconds. 

   attached()  - Returns true if there is a servo attached. 

   detach()    - Stops an attached servos from pulsing its i/o pin. 
  

The library takes about 824 bytes of program memory and 32+(1*servos) bytes of SRAM. 
The pulse width timing is accurate to within 1%

 */

// ensure this library description is only included once
#ifndef ServoTimer2_h
#define ServoTimer2_h

#include <inttypes.h>
typedef uint8_t boolean;
typedef uint8_t byte;

#define MIN_PULSE_WIDTH       750        // the shortest pulse sent to a servo  
#define MAX_PULSE_WIDTH      2250        // the longest pulse sent to a servo 
#define DEFAULT_PULSE_WIDTH  1500        // default pulse width when servo is attached
#define FRAME_SYNC_PERIOD   20000        // total frame duration in microseconds 
#define NBR_CHANNELS 8                   // the maximum number of channels, don't change this 

typedef struct  {
      uint8_t nbr        :5 ;  // a pin number from 0 to 31
      uint8_t isActive   :1 ;  // false if this channel not enabled, pin only pulsed if true 
   } ServoPin_t   ;  

typedef struct {
  ServoPin_t Pin;
  byte counter;
  byte remainder;
}  servo_t;

class ServoTimer2
{
  public:
      // constructor:
      ServoTimer2();

      uint8_t attach(int);     // attach the given pin to the next free channel, sets pinMode, returns channel number or 0 if failure
                               // the attached servo is pulsed with the current pulse width value, (see the write method) 
      uint8_t attach(int, int, int); // as above but also sets min and max values for writes. 
    void detach();
    void write(int);         // store the pulse width in microseconds (between MIN_PULSE_WIDTH and MAX_PULSE_WIDTH)for this channel
    int read();                    // returns current pulse width in microseconds for this servo
      boolean attached();      // return true if this servo is attached 
 private:
       uint8_t chanIndex;      // index into the channel data for this servo

};


// the following ServoArrayT2 class is not implemented in the first version of this library
class ServoArrayT2
{
  public:
      // constructor:
      ServoArrayT2();

      uint8_t attach(int);     // attach the given pin to the next free channel, sets pinMode, returns channel number or 0 if failure
                               // channels are assigned consecutively starting from 1
                               // the attached servo is pulsed with the current pulse width value, (see the write method) 
    void detach(int);        // detach the servo on the given channel
      void write(int,int);     // store the pulse width in microseconds (between MIN_PULSE_WIDTH and MAX_PULSE_WIDTH)for the given channel
    int read(int);                    // returns current pulse width in microseconds for the given channel
      boolean attached(int);   // return true if the servo on the given channel is attached 
 private:
       uint8_t chanIndex;      // index into the channel data for this servo

};

#endif