Squashed commit of the following:

commit 87d0a94443a830510923829fe87e89442c7f3bbe
Author: Asbelos <asbelos@btinternet.com>
Date:   Sun Feb 16 14:40:09 2025 +0000

    Update version.h

commit 8c051710c6
Author: Asbelos <asbelos@btinternet.com>
Date:   Sun Feb 16 10:57:54 2025 +0000

    Now working

commit 6095bf2b3b
Author: Asbelos <asbelos@btinternet.com>
Date:   Sat Feb 15 01:06:55 2025 +0000

    Untested dcc q implementation

commit 52ecab10a7
Author: Asbelos <asbelos@btinternet.com>
Date:   Sat Feb 15 00:22:50 2025 +0000

    Initial dcc queue manager

DCC.cpp

@@ -38,6 +38,7 @@
 #include "TrackManager.h"
 #include "DCCTimer.h"
 #include "Railcom.h"
+#include "DCCQueue.h"
 
 // This module is responsible for converting API calls into
 // messages to be sent to the waveform generator.
@@ -157,8 +158,8 @@ void DCC::setThrottle2( uint16_t cab, byte speedCode)  {
     b[nB++] = speedCode; // for encoding see setThrottle
 
   }
-
+  if ((speedCode & 0x7F) == 1) DCCQueue::scheduleEstopPacket(b, nB, 4, cab); // highest priority
-  DCCWaveform::mainTrack.schedulePacket(b, nB, 0);
+  else DCCQueue::scheduleDCCSpeedPacket( b, nB, 4, cab);
 }
 
 void DCC::setFunctionInternal(int cab, byte byte1, byte byte2, byte count) {
@@ -172,7 +173,7 @@ void DCC::setFunctionInternal(int cab, byte byte1, byte byte2, byte count) {
   if (byte1!=0) b[nB++] = byte1;
   b[nB++] = byte2;
 
-  DCCWaveform::mainTrack.schedulePacket(b, nB, count);
+  DCCQueue::scheduleDCCPacket(b, nB, count);
 }
 
 // returns speed steps 0 to 127 (1 == emergency stop)
@@ -238,7 +239,7 @@ bool DCC::setFn( int cab, int16_t functionNumber, bool on) {
        b[nB++] = (functionNumber & 0x7F) | (on ? 0x80 : 0);  // low order bits and state flag
        b[nB++] = functionNumber >>7 ;  // high order bits
     }
-    DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
+    DCCQueue::scheduleDCCPacket(b, nB, 4);
   }
   // We use the reminder table up to 28 for normal functions.
   // We use 29 to 31 for DC frequency as well so up to 28
@@ -339,16 +340,17 @@ void DCC::setAccessory(int address, byte port, bool gate, byte onoff /*= 2*/) {
   // second byte is of the form 1AAACPPG, where C is 1 for on, PP the ports 0 to 3 and G the gate (coil).
   b[0] = address % 64 + 128;
   b[1] = ((((address / 64) % 8) << 4) + (port % 4 << 1) + gate % 2) ^ 0xF8;
-  if (onoff != 0) {
+  if (onoff==0) {   // off packet only
-    DCCWaveform::mainTrack.schedulePacket(b, 2, 3);      // Repeat on packet three times
-#if defined(EXRAIL_ACTIVE)
-    RMFT2::activateEvent(address<<2|port,gate);
-#endif
-  }
-  if (onoff != 1) {
     b[1] &= ~0x08; // set C to 0
-    DCCWaveform::mainTrack.schedulePacket(b, 2, 3);      // Repeat off packet three times
+    DCCQueue::scheduleDCCPacket(b, 2, 3);
-  }
+  } else if (onoff==1) { // on packet only
+    DCCQueue::scheduleDCCPacket(b, 2, 3);
+  } else { // auto timed on then off  
+    DCCQueue::scheduleAccOnOffPacket(b, 2, 3, 100); // On then off after 100mS
+  } 
+#if defined(EXRAIL_ACTIVE)
+  if (onoff !=0) RMFT2::activateEvent(address<<2|port,gate);
+#endif
 }
 
 bool DCC::setExtendedAccessory(int16_t address, int16_t value, byte repeats) {
@@ -398,7 +400,7 @@ whole range of the 11 bits sent to track.
     | (((~(address>>8)) & 0x07)<<4)  // shift out 8, invert, mask 3 bits, shift up 4
     | ((address & 0x03)<<1);         // mask 2 bits, shift up 1
   b[2]=value;
-  DCCWaveform::mainTrack.schedulePacket(b, sizeof(b), repeats);
+  DCCQueue::scheduleDCCPacket(b, sizeof(b), repeats);
   return true;
 }
 
@@ -417,7 +419,7 @@ void DCC::writeCVByteMain(int cab, int cv, byte bValue)  {
   b[nB++] = cv2(cv);
   b[nB++] = bValue;
 
-  DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
+  DCCQueue::scheduleDCCPacket(b, nB, 4);
 }
 
 //
@@ -435,7 +437,7 @@ void DCC::readCVByteMain(int cab, int cv, ACK_CALLBACK callback)  {
   b[nB++] = cv2(cv);
   b[nB++] = 0;
 
-  DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
+  DCCQueue::scheduleDCCPacket(b, nB, 4);
   Railcom::anticipate(cab,cv,callback);
 }
 
@@ -457,7 +459,7 @@ void DCC::writeCVBitMain(int cab, int cv, byte bNum, bool bValue)  {
   b[nB++] = cv2(cv);
   b[nB++] = WRITE_BIT | (bValue ? BIT_ON : BIT_OFF) | bNum;
 
-  DCCWaveform::mainTrack.schedulePacket(b, nB, 4);
+  DCCQueue::scheduleDCCPacket(b, nB, 4);
 }
 
 bool DCC::setTime(uint16_t minutes,uint8_t speed, bool suddenChange) {
@@ -494,7 +496,7 @@ b[1]=0b11000001; // 1100-0001 (model time)
 b[2]=minutes % 60 ;  // MM
 b[3]= 0b11100000 | (minutes/60); // 111H-HHHH weekday not supported
 b[4]= (suddenChange ? 0b10000000 : 0) | speed;
-DCCWaveform::mainTrack.schedulePacket(b, sizeof(b), 2);
+DCCQueue::scheduleDCCPacket(b, sizeof(b), 2);
 return true; 
 }
 
@@ -844,12 +846,17 @@ byte DCC::loopStatus=0;
 
 void DCC::loop()  {
   TrackManager::loop(); // power overload checks
-  issueReminders();
+  if (DCCWaveform::mainTrack.isReminderWindowOpen()) {
+    // Now is a good time to choose a packet to be sent
+    // Either highest priority from the queues or a reminder
+    if (!DCCQueue::scheduleNext()) {
+      issueReminders();
+      DCCQueue::scheduleNext(); // push through any just created reminder
+    }
+  }
 }
 
 void DCC::issueReminders() {
-  // if the main track transmitter still has a pending packet, skip this time around.
-  if (!DCCWaveform::mainTrack.isReminderWindowOpen()) return;
   // Move to next loco slot.  If occupied, send a reminder.
   auto slot = nextLocoReminder;
   if (slot >= &speedTable[MAX_LOCOS]) slot=&speedTable[0];  // Go to start of table

DCCQueue.cpp

@@ -0,0 +1,185 @@
+/*
+ *  © 2025 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/>.
+ */
+
+
+#include "Arduino.h"
+#include "defines.h"
+#include "DCCQueue.h"
+#include "DCCWaveform.h"
+#include "DIAG.h"
+
+// create statics 
+DCCQueue* DCCQueue::lowPriorityQueue=new DCCQueue();
+DCCQueue* DCCQueue::highPriorityQueue=new DCCQueue();
+PendingSlot* DCCQueue::recycleList=nullptr;
+
+    DCCQueue::DCCQueue() {
+        head=nullptr;
+        tail=nullptr;
+    }
+    
+    void DCCQueue::addQueue(PendingSlot* p) {
+        if (tail) tail->next=p;
+        else head=p;
+        tail=p;
+        p->next=nullptr;          
+    }
+
+    void DCCQueue::jumpQueue(PendingSlot* p) {
+        p->next=head;
+        head=p;
+        if (!tail) tail=p; 
+    }
+
+    
+    void DCCQueue::recycle(PendingSlot* p) {
+        p->next=recycleList;
+        recycleList=p;
+    }
+    
+    // Packet joins end of low priority queue.
+    void DCCQueue::scheduleDCCPacket(byte* packet, byte length, byte repeats) {
+        lowPriorityQueue->addQueue(getSlot(NORMAL_PACKET,packet,length,repeats,0));
+    }
+    
+    // Packet replaces existing loco speed packet or joins end of high priority queue. 
+    
+    void DCCQueue::scheduleDCCSpeedPacket(byte* packet, byte length, byte repeats, uint16_t loco) {
+        for (auto p=highPriorityQueue->head;p;p=p->next) {
+            if (p->locoId==loco) {
+                // replace existing packet
+                memcpy(p->packet,packet,length);
+                p->packetLength=length;
+                p->packetRepeat=repeats;
+                return;
+            }
+        }
+        highPriorityQueue->addQueue(getSlot(NORMAL_PACKET,packet,length,repeats,loco));
+    }
+    
+    
+    // ESTOP -  
+    // any outstanding throttle packet for this loco (all if loco=0) discarded
+    // Packet joins start of queue,
+   
+    
+    void DCCQueue::scheduleEstopPacket(byte* packet, byte length, byte repeats,uint16_t loco) {
+        
+        // DIAG(F("DCC ESTOP loco=%d"),loco);
+       
+        // kill any existing throttle packets for this loco
+        PendingSlot * previous=nullptr;
+        auto p=highPriorityQueue->head;
+        while(p) {
+            if (loco==0 || p->locoId==loco) {
+                // drop this packet from the highPriority   queue 
+                if (previous) previous->next=p->next;
+                else highPriorityQueue->head=p->next;
+                
+                recycle(p);  // recycle this slot
+
+                // address next packet
+                p=previous?previous->next : highPriorityQueue->head;
+            }
+            else {
+                previous=p;
+                p=p->next;
+            }
+        }
+        // add the estop packet to the start of the queue
+        highPriorityQueue->jumpQueue(getSlot(NORMAL_PACKET,packet,length,repeats,0));
+    }
+
+    // Accessory gate-On Packet joins end of queue as normal.
+    // When dequeued, packet is retained at start of queue 
+    // but modified to gate-off and given the delayed start.
+    // getNext will ignore this packet until the requested start time. 
+    void DCCQueue::scheduleAccOnOffPacket(byte* packet, byte length, byte repeats,int16_t delayms) {
+        auto p=getSlot(ACC_ON_PACKET,packet,length,repeats,0);
+        p->delayOff=delayms;
+        lowPriorityQueue->addQueue(p);
+    };
+
+    
+    // Obtain packet (fills packet, length and repeats) 
+    // returns 0 length if nothing in queue.
+
+    bool DCCQueue::scheduleNext() {
+        // check high priority queue first
+        if (!DCCWaveform::mainTrack.isReminderWindowOpen()) return false;
+        PendingSlot* previous=nullptr;
+        for (auto p=highPriorityQueue->head;p;p=p->next) {
+            // skip over pending ACC_OFF packets which are still delayed
+            if (p->type == ACC_OFF_PACKET && millis()<p->startTime) continue;
+            // use this slot
+            DCCWaveform::mainTrack.schedulePacket(p->packet,p->packetLength,p->packetRepeat);
+            // remove this slot from the queue 
+            if (previous) previous->next=p->next;
+            else highPriorityQueue->head=p->next;
+            if (!highPriorityQueue->head) highPriorityQueue->tail=nullptr;
+            
+            // and recycle it.
+            recycle(p);     
+            return true;
+        }
+        
+        // No high priopity packets found, check low priority queue
+        auto p=lowPriorityQueue->head;
+        if (!p) return false;  // nothing in queues
+        
+        // schedule first packet in queue 
+        DCCWaveform::mainTrack.schedulePacket(p->packet,p->packetLength,p->packetRepeat);
+
+        // remove from queue
+        lowPriorityQueue->head=p->next;
+        if (!lowPriorityQueue->head) lowPriorityQueue->tail=nullptr;
+        
+        if (p->type == ACC_ON_PACKET) {
+                // convert to a delayed off packet and jump the high priority queue
+                p->type= ACC_OFF_PACKET;
+                p->packet[1]  &= ~0x08; // set C to 0 (gate off) 
+                p->startTime=millis()+p->delayOff;
+                highPriorityQueue->jumpQueue(p);
+                }
+        else recycle(p);  // recycle this slot
+        return true;   
+    }
+    
+    // obtain and initialise slot for a PendingSlot.
+    PendingSlot*  DCCQueue::getSlot(PendingType type, byte* packet, byte length, byte repeats,uint16_t loco) {
+        PendingSlot * p; 
+        if (recycleList) {
+            p=recycleList;
+            recycleList=p->next;
+        }
+        else { 
+            DIAG(F("New DCC queue slot"));
+            p=new PendingSlot; // need a queue entry 
+        }
+        p->next=nullptr;
+        p->type=type;
+        p->packetLength=length;
+        p->packetRepeat=repeats; 
+        memcpy((void*)p->packet,packet,length);
+        p->locoId=loco;
+        return p; 
+    }
+
+    

DCCQueue.h

@@ -0,0 +1,84 @@
+/*
+ *  © 2025 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 DCCQueue_h
+#define DCCQueue_h
+#include "Arduino.h"
+#include "DCCWaveform.h"
+
+enum PendingType:byte {NORMAL_PACKET,ACC_ON_PACKET,ACC_OFF_PACKET,DEAD_PACKET};
+  struct PendingSlot {
+      PendingSlot* next; 
+      PendingType type;
+      byte packetLength;
+      byte packetRepeat;
+      byte packet[MAX_PACKET_SIZE];
+      
+      union { // use depends on packet type
+        uint16_t locoId;    // NORMAL_PACKET .. only set >0 for speed change packets 
+                            // so they can be easily discarded if an estop jumps the queue.
+        uint16_t delayOff;  // ACC_ON_PACKET delay to apply between on/off
+        uint32_t startTime; // ACC_OFF_PACKET time (mS) to transmit 
+      };
+  };
+  
+class DCCQueue {
+  public:
+    
+    
+    // Non-speed packets are queued in the main queue
+    static void scheduleDCCPacket(byte* packet, byte length, byte repeats);
+
+    // Speed packets are queued in the high priority queue
+    static void scheduleDCCSpeedPacket(byte* packet, byte length, byte repeats, uint16_t loco);
+    
+    // ESTOP packets jump the high priority queue and discard any outstanding throttle packets for this loco  
+    static void scheduleEstopPacket(byte* packet, byte length, byte repeats,uint16_t loco);
+
+    // Accessory gate-On Packet joins end of main queue as normal. 
+    // When dequeued, packet is modified to gate-off and given the delayed start in the high priority queue. 
+    // getNext will ignore this packet until the requested start time.
+    static void scheduleAccOnOffPacket(byte* packet, byte length, byte repeats,int16_t delayms);
+
+  
+    // Schedules a main track packet from the queues if none pending.  
+    // returns true if a packet was scheduled.
+    static bool scheduleNext(); 
+
+  private:
+  
+  // statics to manage high and low priority queues and recycleing of PENDINGs
+    static PendingSlot* recycleList;
+    static DCCQueue* highPriorityQueue;
+    static DCCQueue* lowPriorityQueue;
+
+    DCCQueue();
+    
+    PendingSlot*  head;
+    PendingSlot * tail;
+    
+    // obtain and initialise slot for a PendingSlot. 
+    static PendingSlot*  getSlot(PendingType type, byte* packet, byte length, byte repeats, uint16_t loco);
+    static void recycle(PendingSlot* p);
+    void addQueue(PendingSlot * p);
+    void jumpQueue(PendingSlot * p);
+  
+};
+#endif

version.h

@@ -3,7 +3,8 @@
 
 #include "StringFormatter.h"
 
-#define VERSION "5.5.13"
+#define VERSION "5.5.14"
+// 5.5.14 - DCC Non-blocking packet queue with priority
 // 5.5.13 - Update STM32duino core to v19.0.0. for updated PeripheralPins.c in preparation for F429/439ZI Ethernet support 
 // 5.5.12 - Websocket support (wifi only) 
 // 5.5.11 - (5.4.2) accessory command reverse