Add CMRI work-arounds for ArduinoCMRI library

Work-arounds enabled by "#define ARDUINOCMRI_COMPATIBLE TRUE" in config.h

IO_CMRI.cpp

@@ -18,6 +18,7 @@
  */
 
 #include "IO_CMRI.h"
+#include "defines.h"
 
 /************************************************************
  * CMRIbus implementation
@@ -36,12 +37,18 @@ CMRIbus::CMRIbus(uint8_t busNo, HardwareSerial &serial, unsigned long baud, uint
   }
 
   // Max message length is 256+6=262 bytes.  
-  // Each byte is one start bit, 8 data bits and 1 stop bit = 10 bits per byte.  
+  // Each byte is one start bit, 8 data bits and 1 or 2 stop bits, assume 11 bits per byte.  
-  // Calculate timeout based on double this time.
+  // Calculate timeout based on treble this time.
-  _timeoutPeriod = 2 * 10 * 262 * 1000UL / (_baud / 1000UL);
+  _timeoutPeriod = 3 * 11 * 262 * 1000UL / (_baud / 1000UL);
-
+#if ARDUINOCMRI_COMPATIBLE
-  // Calculate the time in microseconds to transmit one byte (10 bits).
+  // NOTE: The ArduinoCMRI library, unless modified, contains a 'delay(50)' between 
-  _byteTransmitTime = 1000000UL * 10 / _baud;
+  // receiving the end of the prompt message and starting to send the response.  This
+  // is allowed for below.
+  _timeoutPeriod += 50000UL;
+#endif
+  
+  // Calculate the time in microseconds to transmit one byte (11 bits max).
+  _byteTransmitTime = 1000000UL * 11 / _baud;
   // Postdelay is only required if we need to allow for data still being sent when
   // we want to switch off the transmitter.  The flush() method of HardwareSerial
   // ensures that the data has completed being sent over the line.
@@ -148,9 +155,9 @@ void CMRIbus::processOutgoing() {
     case TD_TRANSMIT:
       charsSent = sendData(_currentNode);
       _transmitState = TD_PROMPT;
-        // Defer next entry for as long as it takes to transmit the characters, 
+      // Defer next entry for as long as it takes to transmit the characters, 
-        // to allow output queue to empty.
+      // to allow output queue to empty.  Allow 2 bytes extra.
-      delayUntil(_currentMicros+_byteTransmitTime*charsSent);
+      delayUntil(_currentMicros+_byteTransmitTime*(charsSent+2));
       break;
     case TD_PROMPT:
       charsSent = requestData(_currentNode);
@@ -184,7 +191,7 @@ void CMRIbus::processIncoming() {
       if (data == SYN) nextState = RD_SYN2; 
       break;
     case RD_SYN2:
-      if (data == SYN) nextState = RD_STX; 
+      if (data == SYN) nextState = RD_STX; else nextState = RD_SYN2;
       break;
     case RD_STX:
       if (data == STX) nextState = RD_ADDR;
@@ -225,9 +232,17 @@ void CMRIbus::processIncoming() {
 void CMRIbus::enableTransmitter() {
   if (_transmitEnablePin != VPIN_NONE) 
     ArduinoPins::fastWriteDigital(_transmitEnablePin, 1);
-  // Send an extra SYN character to ensure transmitter and 
+  // If we need a delay before we start the packet header, 
-  // remote receiver have stabilised before we start the packet.
+  // we can send a character or two to synchronise the 
+  // transmitter and receiver.
+  // SYN characters should be used, but a bug in the
+  // ArduinoCMRI library causes it to ignore the packet if
+  // it's preceded by an odd number of SYN characters.
+  // So send a SYN followed by a NUL in that case.
   _serial->write(SYN);
+#if ARDUINOCMRI_COMPATIBLE
+  _serial->write(NUL);  // Reset the ArduinoCMRI library's parser
+#endif
 }
 
 // If configured for half duplex RS485, switch RS485 interface

IO_CMRI.h

@@ -18,6 +18,8 @@
  */
 
 /*
+ * CMRIbus
+ * =======
  * To define a CMRI bus, example syntax:
  *    CMRIbus::create(bus, serial, baud[, cycletime[, pin]]);
  * 
@@ -29,6 +31,15 @@
  * 
  * Each bus must use a different serial port.
  * 
+ * IMPORTANT: If you are using ArduinoCMRI library code by Michael Adams, at the time of writing this library
+ * is not compliant with the LCS-9.10.1 specification for CMRInet protocol.  
+ * Various work-arounds may be enabled within the driver by adding the following line to your config.h file,
+ * to allow nodes running the ArduinoCMRI library to communicate:
+ * 
+ *  #define ARDUINOCMRI_COMPATIBLE TRUE
+ * 
+ * CMRINode
+ * ========
  * To define a CMRI node and associate it with a CMRI bus,
  *    CMRInode::create(firstVPIN, numVPINs, bus, address, type [, inputs, outputs]);
  * 
@@ -196,6 +207,7 @@ private:
 
   // Definition of special characters in CMRInet protocol
   enum : uint8_t {
+    NUL = 0x00,
     STX = 0x02,
     ETX = 0x03,
     DLE = 0x10,
@@ -209,8 +221,12 @@ public:
 
   // Device-specific initialisation
   void _begin() override {
-    // Some sources quote one stop bit, some two.
+    // CMRInet spec states one stop bit, JMRI and ArduinoCMRI use two stop bits
+#if ARDUINOCMRI_COMPATIBLE
+    _serial->begin(_baud, SERIAL_8N2);
+#else
     _serial->begin(_baud, SERIAL_8N1);
+#endif
   #if defined(DIAG_IO)
     _display();
   #endif