CommandStation-EX/DCCWaveform.cpp

/*
 *  © 2021 Neil McKechnie
 *  © 2021 Mike S
 *  © 2021 Fred Decker
 *  © 2020-2021 Harald Barth
 *  © 2020-2021 Chris Harlow
 *  All rights reserved.
 *  
 *  This file is part of CommandStation-EX
 *
 *  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/>.
 */
#ifndef ARDUINO_ARCH_ESP32
  // This code is replaced entirely on an ESP32
#include <Arduino.h>

#include "DCCWaveform.h"
#include "TrackManager.h"
#include "DCCTimer.h"
#include "DCCACK.h"
#include "DIAG.h"


DCCWaveform  DCCWaveform::mainTrack(PREAMBLE_BITS_MAIN, true);
DCCWaveform  DCCWaveform::progTrack(PREAMBLE_BITS_PROG, false);


// This bitmask has 9 entries as each byte is trasmitted as a zero + 8 bits.
const byte bitMask[] = {0x00, 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01};

const byte idlePacket[] = {0xFF, 0x00, 0xFF};
const byte resetPacket[] = {0x00, 0x00, 0x00};


// For each state of the wave  nextState=stateTransform[currentState] 
const WAVE_STATE stateTransform[]={
   /* WAVE_START   -> */ WAVE_PENDING,
   /* WAVE_MID_1   -> */ WAVE_START,
   /* WAVE_HIGH_0  -> */ WAVE_MID_0,
   /* WAVE_MID_0   -> */ WAVE_LOW_0,
   /* WAVE_LOW_0   -> */ WAVE_START,
   /* WAVE_PENDING (should not happen) -> */ WAVE_PENDING};

// For each state of the wave, signal pin is HIGH or LOW   
const bool signalTransform[]={
   /* WAVE_START   -> */ HIGH,
   /* WAVE_MID_1   -> */ LOW,
   /* WAVE_HIGH_0  -> */ HIGH,
   /* WAVE_MID_0   -> */ LOW,
   /* WAVE_LOW_0   -> */ LOW,
   /* WAVE_PENDING (should not happen) -> */ LOW};

void DCCWaveform::begin() {
  DCCTimer::begin(DCCWaveform::interruptHandler);     
}

void DCCWaveform::loop() {
 // empty placemarker in case ESP32 needs something here 
}

#pragma GCC push_options
#pragma GCC optimize ("-O3")
void DCCWaveform::interruptHandler() {
  // call the timer edge sensitive actions for progtrack and maintrack
  // member functions would be cleaner but have more overhead
  byte sigMain=signalTransform[mainTrack.state];
  byte sigProg=TrackManager::progTrackSyncMain? sigMain : signalTransform[progTrack.state];
  
  // Set the signal state for both tracks
  TrackManager::setDCCSignal(sigMain);
  TrackManager::setPROGSignal(sigProg);
  
  // Move on in the state engine
  mainTrack.state=stateTransform[mainTrack.state];    
  progTrack.state=stateTransform[progTrack.state];    


  // WAVE_PENDING means we dont yet know what the next bit is
  if (mainTrack.state==WAVE_PENDING) mainTrack.interrupt2();  
  if (progTrack.state==WAVE_PENDING) progTrack.interrupt2();
  else DCCACK::checkAck(progTrack.sentResetsSincePacket);

}
#pragma GCC pop_options

// An instance of this class handles the DCC transmissions for one track. (main or prog)
// Interrupts are marshalled via the statics.
// A track has a current transmit buffer, and a pending buffer.
// When the current buffer is exhausted, either the pending buffer (if there is one waiting) or an idle buffer.



DCCWaveform::DCCWaveform( byte preambleBits, bool isMain) {
  isMainTrack = isMain;
  packetPending = false;
  memcpy(transmitPacket, idlePacket, sizeof(idlePacket));
  state = WAVE_START;
  // The +1 below is to allow the preamble generator to create the stop bit
  // for the previous packet. 
  requiredPreambles = preambleBits+1;  
  bytes_sent = 0;
  bits_sent = 0;
}



#pragma GCC push_options
#pragma GCC optimize ("-O3")
void DCCWaveform::interrupt2() {
  // calculate the next bit to be sent:
  // set state WAVE_MID_1  for a 1=bit
  //        or WAVE_HIGH_0 for a 0 bit.

  if (remainingPreambles > 0 ) {
    state=WAVE_MID_1;  // switch state to trigger LOW on next interrupt
    remainingPreambles--;
    // Update free memory diagnostic as we don't have anything else to do this time.
    // Allow for checkAck and its called functions using 22 bytes more.
    DCCTimer::updateMinimumFreeMemoryISR(22); 
    return;
  }

  // Wave has gone HIGH but what happens next depends on the bit to be transmitted
  // beware OF 9-BIT MASK  generating a zero to start each byte
  state=(transmitPacket[bytes_sent] & bitMask[bits_sent])? WAVE_MID_1 : WAVE_HIGH_0; 
  bits_sent++;

  // If this is the last bit of a byte, prepare for the next byte

  if (bits_sent == 9) { // zero followed by 8 bits of a byte
    //end of Byte
    bits_sent = 0;
    bytes_sent++;
    // if this is the last byte, prepere for next packet
    if (bytes_sent >= transmitLength) {
      // end of transmission buffer... repeat or switch to next message
      bytes_sent = 0;
      remainingPreambles = requiredPreambles;

      if (transmitRepeats > 0) {
        transmitRepeats--;
      }
      else if (packetPending) {
        // Copy pending packet to transmit packet
        // a fixed length memcpy is faster than a variable length loop for these small lengths
        // for (int b = 0; b < pendingLength; b++) transmitPacket[b] = pendingPacket[b];
        memcpy( transmitPacket, pendingPacket, sizeof(pendingPacket));
        
        transmitLength = pendingLength;
        transmitRepeats = pendingRepeats;
        packetPending = false;
        sentResetsSincePacket=0;
      }
      else {
        // Fortunately reset and idle packets are the same length
        memcpy( transmitPacket, isMainTrack ? idlePacket : resetPacket, sizeof(idlePacket));
        transmitLength = sizeof(idlePacket);
        transmitRepeats = 0;
        if (sentResetsSincePacket<250) sentResetsSincePacket++;
      }
    }
  }  
}
#pragma GCC pop_options

// Wait until there is no packet pending, then make this pending
void DCCWaveform::schedulePacket(const byte buffer[], byte byteCount, byte repeats) {
  if (byteCount > MAX_PACKET_SIZE) return; // allow for chksum
  while (packetPending);

  byte checksum = 0;
  for (byte b = 0; b < byteCount; b++) {
    checksum ^= buffer[b];
    pendingPacket[b] = buffer[b];
  }
  // buffer is MAX_PACKET_SIZE but pendingPacket is one bigger
  pendingPacket[byteCount] = checksum;
  pendingLength = byteCount + 1;
  pendingRepeats = repeats;
  packetPending = true;
  sentResetsSincePacket=0;
}
#endif