CommandStation-EX/DCCTimer.cpp

/*
 *  © 2021, Chris Harlow & David Cutting. All rights reserved.
 *  
 *  This file is part of Asbelos DCC API
 *
 *  This is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  It 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
 */


/* This timer class is used to manage the single timer required to handle the DCC waveform.
 *  All timer access comes through this class so that it can be compiled for 
 *  various hardware CPU types. 
 *  
 *  DCCEX works on a single timer interrupt at a regular 58uS interval.
 *  The DCCWaveform class generates the signals to the motor shield  
 *  based on this timer. 
 */

#include "DCCTimer.h"
const int DCC_SIGNAL_TIME=58;  // this is the 58uS DCC 1-bit waveform half-cycle 
const long CLOCK_CYCLES=(F_CPU / 1000000 * DCC_SIGNAL_TIME) >>1;

INTERRUPT_CALLBACK interruptHandler=0;

#ifdef ARDUINO_ARCH_MEGAAVR
  // Arduino unoWifi Rev2 and nanoEvery architectire 
  void DCCTimer::begin(INTERRUPT_CALLBACK callback) {
    interruptHandler=callback;
    noInterrupts(); 
    ADC0.CTRLC = (ADC0.CTRLC & 0b00110000) | 0b01000011;  // speed up analogRead sample time   
    TCB0.CTRLB = TCB_CNTMODE_INT_gc & ~TCB_CCMPEN_bm; // timer compare mode with output disabled
    TCB0.CTRLA = TCB_CLKSEL_CLKDIV2_gc; //   8 MHz ~ 0.125 us      
    TCB0.CCMP =  CLOCK_CYCLES -1;  // 1 tick less for timer reset 
    TCB0.INTFLAGS = TCB_CAPT_bm; // clear interrupt request flag
    TCB0.INTCTRL = TCB_CAPT_bm;  // Enable the interrupt
    TCB0.CNT = 0;
    TCB0.CTRLA |= TCB_ENABLE_bm;  // start
    interrupts();
  }

  // ISR called by timer interrupt every 58uS
  ISR(TCB0_INT_vect){
    TCB0.INTFLAGS = TCB_CAPT_bm;
    interruptHandler();
  }
  
#else 
  // Arduino nano, uno, mega etc 
  void DCCTimer::begin(INTERRUPT_CALLBACK callback) {
    interruptHandler=callback;
    noInterrupts(); 
    ADCSRA = (ADCSRA & 0b11111000) | 0b00000100;   // speed up analogRead sample time 
    TCCR1A = 0;
    ICR1 = CLOCK_CYCLES;
    TCNT1 = 0;   
    TCCR1B = _BV(WGM13) | _BV(CS10);     // Mode 8, clock select 1
    TIMSK1 = _BV(TOIE1); // Enable Software interrupt
    interrupts();
  }

// ISR called by timer interrupt every 58uS
  ISR(TIMER1_OVF_vect){ interruptHandler(); }
#endif