reasonable start

DCCEXParser.cpp

@@ -1035,7 +1035,13 @@ bool DCCEXParser::parseC(Print *stream, int16_t params, int16_t p[]) {
         DCC::setGlobalSpeedsteps(128);
 	DIAG(F("128 Speedsteps"));
         return true;
-
+    case "RAILCOM"_hk:
+        {
+        bool onOff = (params > 1) && (p[1] == 1 || p[1] == "ON"_hk); // dont care if other stuff or missing... just means off
+        DIAG(F("Railcom %S")
+            ,DCCWaveform::setRailcom(onOff)?F("ON"):F("OFF"));
+        return true;     
+        }
 #ifndef DISABLE_PROG
     case "ACK"_hk: // <D ACK ON/OFF> <D ACK [LIMIT|MIN|MAX|RETRY] Value>
 	if (params >= 3) {

DCCTimer.h

@@ -62,6 +62,8 @@ class DCCTimer {
   static bool isPWMPin(byte pin);
   static void setPWM(byte pin, bool high);
   static void clearPWM();
+  static void startRailcomTimer(byte brakePin);
+  static void ackRailcomTimer();
   static void DCCEXanalogWriteFrequency(uint8_t pin, uint32_t frequency);
   static void DCCEXanalogWrite(uint8_t pin, int value);
 

DCCTimerAVR.cpp

@@ -39,6 +39,9 @@ INTERRUPT_CALLBACK interruptHandler=0;
     #define TIMER1_A_PIN   11
     #define TIMER1_B_PIN   12
     #define TIMER1_C_PIN   13
+    #define TIMER2_A_PIN   10
+    #define TIMER2_B_PIN   9
+    
 #else
    #define TIMER1_A_PIN   9
    #define TIMER1_B_PIN   10
@@ -55,6 +58,53 @@ void DCCTimer::begin(INTERRUPT_CALLBACK callback) {
     interrupts();
   }
 
+
+void DCCTimer::startRailcomTimer(byte brakePin) {
+  /* The Railcom timer is started in such a way that it 
+     - First triggers 28uS after the last TIMER1 tick. 
+       This provides an accurate offset (in High Accuracy mode)
+       for the start of the Railcom cutout.
+     - Sets the Railcom pin high at first tick, 
+       because its been setup with 100% PWM duty cycle.
+        
+     - Cycles at 436uS so the second tick is the 
+        correct distance from the cutout.
+        
+     - Waveform code is responsible for altering the PWM 
+       duty cycle to 0% any time between the first and last tick.
+       (there will be 7 DCC timer1 ticks in which to do this.)
+    
+    */
+  const int cutoutDuration = 436; // Desired interval in microseconds
+  
+  // Set up Timer2 for CTC mode (Clear Timer on Compare Match)
+  TCCR2A = 0; // Clear Timer2 control register A
+  TCCR2B = 0; // Clear Timer2 control register B
+  TCNT2 = 0;  // Initialize Timer2 counter value to 0
+   // Configure Phase and Frequency Correct PWM mode
+//TCCR2A = (1 << COM2B1) | (1 << WGM20) | (1 << WGM21);
+  
+  // Set Fast PWM mode with non-inverted output on OC2B (pin 9)
+  TCCR2A = (1 << WGM21) | (1 << WGM20) | (1 << COM2B1);
+  // Set Timer 2 prescaler to 32
+  TCCR2B = (1 << CS21) | (1 << CS20); // 32 prescaler
+
+  // Set the compare match value for desired interval
+  OCR2A = (F_CPU / 1000000) * cutoutDuration / 32 - 1;
+
+  // Calculate the compare match value for desired duty cycle
+  OCR2B = OCR2A+1;  // set duty cycle to 100%= OCR2A)
+
+  // Enable Timer2 output on pin 9 (OC2B)
+  DDRB |= (1 << DDB1);
+  // TODO Fudge TCNT2 to sync with last tcnt1 tick + 28uS
+}
+
+void DCCTimer::ackRailcomTimer() {
+  OCR2B= 0x00;  // brfake pin pwm duty cycle 0 at next tick
+}
+
+
 // ISR called by timer interrupt every 58uS
   ISR(TIMER1_OVF_vect){ interruptHandler(); }
 

DCCWaveform.cpp

@@ -116,7 +116,18 @@ DCCWaveform::DCCWaveform( byte preambleBits, bool isMain) {
   bits_sent = 0;
 }
     
+volatile bool DCCWaveform::railcomActive=false;     // switched on by user
 
+bool DCCWaveform::setRailcom(bool on) {
+  if (on) {
+    // TODO check possible
+    railcomActive=true;
+  }
+  else {
+    railcomActive=false;
+  } 
+  return railcomActive;
+}
 
 #pragma GCC push_options
 #pragma GCC optimize ("-O3")
@@ -124,7 +135,6 @@ 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--;
@@ -134,6 +144,7 @@ void DCCWaveform::interrupt2() {
     // that the reminder doesn't block a more urgent packet. 
     reminderWindowOpen=transmitRepeats==0 && remainingPreambles<4 && remainingPreambles>1;
     if (remainingPreambles==1) promotePendingPacket();
+    else if (remainingPreambles==10 && isMainTrack && railcomActive) DCCTimer::ackRailcomTimer();
     // 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.
     else DCCTimer::updateMinimumFreeMemoryISR(22); 
@@ -157,6 +168,12 @@ void DCCWaveform::interrupt2() {
       bytes_sent = 0;
       // preamble for next packet will start...
       remainingPreambles = requiredPreambles;
+      
+      // set the railcom coundown to trigger half way 
+      // through the first preamble bit.
+      // Note.. we are still sending the last packet bit
+      //    and we then have to allow for the packet end bit
+      if (isMainTrack && railcomActive) DCCTimer::startRailcomTimer(9);
       }
   }  
 }
@@ -208,7 +225,9 @@ void DCCWaveform::promotePendingPacket() {
       
       // nothing to do, just send idles or resets
       // Fortunately reset and idle packets are the same length
-      memcpy( transmitPacket, isMainTrack ? idlePacket : resetPacket, sizeof(idlePacket));
+  // TEMPORARY DEBUG FOR RAILCOM
+  //      memcpy( transmitPacket, isMainTrack ? idlePacket : resetPacket, sizeof(idlePacket));
+        memcpy( transmitPacket, resetPacket, sizeof(idlePacket));
       transmitLength = sizeof(idlePacket);
       transmitRepeats = 0;
       if (getResets() < 250) sentResetsSincePacket++; // only place to increment (private!)

DCCWaveform.h

@@ -40,7 +40,14 @@ const byte MAX_PACKET_SIZE = 5;     // NMRA standard extended packets, payload s
 
 // The WAVE_STATE enum is deliberately numbered because a change of order would be catastrophic
 // to the transform array.
-enum  WAVE_STATE : byte {WAVE_START=0,WAVE_MID_1=1,WAVE_HIGH_0=2,WAVE_MID_0=3,WAVE_LOW_0=4,WAVE_PENDING=5};
+enum  WAVE_STATE : byte {
+  WAVE_START=0,  // wave going high at start of bit 
+  WAVE_MID_1=1,  // middle of 1 bit 
+  WAVE_HIGH_0=2, // first part of 0 bit high
+  WAVE_MID_0=3,  // middle of 0 bit
+  WAVE_LOW_0=4,  // first part of 0 bit low
+  WAVE_PENDING=5 // next bit not yet known
+  };
 
 // NOTE: static functions are used for the overall controller, then
 // one instance is created for each track.
@@ -78,6 +85,8 @@ class DCCWaveform {
     void schedulePacket(const byte buffer[], byte byteCount, byte repeats);
     bool isReminderWindowOpen();
     void promotePendingPacket();
+    static bool setRailcom(bool on);
+    static bool isRailcom() {return railcomActive;}
     
   private:
 #ifndef ARDUINO_ARCH_ESP32
@@ -103,6 +112,8 @@ class DCCWaveform {
     byte pendingPacket[MAX_PACKET_SIZE+1]; // +1 for checksum
     byte pendingLength;
     byte pendingRepeats;
+    static volatile bool railcomActive;     // switched on by user
+    
 #ifdef ARDUINO_ARCH_ESP32
   static RMTChannel *rmtMainChannel;
   static RMTChannel *rmtProgChannel;

TrackManager.cpp

@@ -157,10 +157,9 @@ void TrackManager::setDCCSignal( bool on) {
   HAVE_PORTF(PORTF=shadowPORTF);
 }
 
+// Called by interrupt context
 void TrackManager::setCutout( bool on) {
-    (void) on;
+    APPLY_BY_MODE(TRACK_MODE_MAIN,setBrake(on,true));
-    // TODO Cutout needs fake ports as well
-    // TODO      APPLY_BY_MODE(TRACK_MODE_MAIN,setCutout(on));
 }
 
 // setPROGSignal(), called from interrupt context