Add configurable transmit delay via set_transmit_delay()

examples/init_handler/init_handler.ino

@@ -18,11 +18,17 @@
  * 3: Open Tools > Tables > Lights and add a light at address 1
  * 4: Open the C/MRI Monitor to watch the INIT message
  *    Raw format: [41 49 43 00 0A ...] = UA 'A', cmd 'I', NDP='C', DL=10
+ *
+ * Wiring:
+ *   Serial (pins 0/1) -> RS-485 transceiver -> host (JMRI)
+ *   SoftwareSerial (pins 10/11) -> Serial Monitor for debug output
  */
 
 #include <CMRI.h>
+#include <SoftwareSerial.h>
 
-CMRI cmri; // defaults to a SMINI with address 0
+SoftwareSerial console(10, 11); // RX, TX for debug output
+CMRI cmri;                      // defaults to a SMINI with address 0, using Serial
 
 // ---------------------------------------------------------------------------
 // INIT handler callback
@@ -32,44 +38,45 @@ CMRI cmri; // defaults to a SMINI with address 0
 // ---------------------------------------------------------------------------
 void on_init(const uint8_t *data, int len)
 {
-	Serial.print(F("INIT received ("));
+	console.print(F("INIT received ("));
 
 	if (len >= 1)
 	{
-		Serial.print(F("NDP="));
-		Serial.write(data[0]);
-		Serial.print(F(" "));
+		console.print(F("NDP="));
+		console.write(data[0]);
+		console.print(F(" "));
 	}
 
 	if (len >= 3)
 	{
 		int delay_us = (data[1] * 256 + data[2]) * 10;
-		Serial.print(F("DL="));
-		Serial.print(delay_us);
-		Serial.print(F("us "));
+		console.print(F("DL="));
+		console.print(delay_us);
+		console.print(F("us "));
 	}
 
 	if (len > 3)
 	{
-		Serial.print(F("options="));
+		console.print(F("options="));
 		for (int i = 3; i < len; i++)
 		{
 			if (i > 3)
-				Serial.print(F(" "));
+				console.print(F(" "));
 			if (data[i] < 16)
-				Serial.print(F("0"));
-			Serial.print(data[i], HEX);
+				console.print(F("0"));
+			console.print(data[i], HEX);
 		}
-		Serial.print(F(" "));
+		console.print(F(" "));
 	}
 
-	Serial.print(len);
-	Serial.println(F(" bytes"));
+	console.print(len);
+	console.println(F(" bytes"));
 }
 
 void setup()
 {
-	Serial.begin(9600, SERIAL_8N2);
+	Serial.begin(9600, SERIAL_8N2); // CMRI bus
+	console.begin(9600);            // debug output
 	cmri.set_init_handler(on_init);
 	pinMode(13, OUTPUT);
 }

examples/init_handler_with_delay/init_handler_with_delay.ino

@@ -0,0 +1,79 @@
+/**
+ * C/MRI INIT handler with transmit delay example
+ * ================================================
+ * Demonstrates how to register an INIT callback that parses the
+ * transmit delay (dH/dL) from the INIT payload and applies it
+ * using set_transmit_delay().
+ *
+ * The INIT message body follows NMRA LCS-9.10.1:
+ *   byte 0:   NDP (Node Definition Parameter)
+ *   bytes 1-2: dH/dL (transmit delay, high & low bytes)
+ *   bytes 3+:  node-type-specific options
+ *
+ * The transmit delay is computed as (dH * 256 + dL) * 10 microseconds.
+ * Modern hosts set dH/dL to zero; non-zero values are for legacy
+ * compatibility. This delay is applied before each GET (R) reply to
+ * allow RS-485 transceiver turnaround.
+ *
+ * To set up in JMRI:
+ * 1: Create a new C/MRI connection (Serial, 9600 baud)
+ * 2: Configure a node with address 0 — JMRI sends an INIT at startup
+ * 3: Open Tools > Tables > Lights and add a light at address 1
+ * 4: Open the C/MRI Monitor to watch the INIT message
+ *
+ * Wiring:
+ *   Serial (pins 0/1) -> RS-485 transceiver -> host (JMRI)
+ *   SoftwareSerial (pins 10/11) -> Serial Monitor for debug output
+ */
+
+#include <CMRI.h>
+#include <SoftwareSerial.h>
+
+SoftwareSerial console(10, 11); // RX, TX for debug output
+CMRI cmri;                      // defaults to a SMINI with address 0, using Serial
+
+// ---------------------------------------------------------------------------
+// INIT handler callback
+// Parses dH/dL and applies the transmit delay via set_transmit_delay().
+// ---------------------------------------------------------------------------
+void on_init(const uint8_t *data, int len)
+{
+	console.print(F("INIT received ("));
+
+	if (len >= 1)
+	{
+		console.print(F("NDP="));
+		console.write(data[0]);
+		console.print(F(" "));
+	}
+
+	if (len >= 3)
+	{
+		unsigned int dH = data[1];
+		unsigned int dL = data[2];
+		unsigned int delay_us = (dH * 256 + dL) * 10;
+
+		cmri.set_transmit_delay(delay_us);
+
+		console.print(F("DL="));
+		console.print(delay_us);
+		console.print(F("us applied "));
+	}
+
+	console.print(len);
+	console.println(F(" bytes"));
+}
+
+void setup()
+{
+	Serial.begin(9600, SERIAL_8N2); // CMRI bus
+	console.begin(9600);            // debug output
+	cmri.set_init_handler(on_init);
+	pinMode(13, OUTPUT);
+}
+
+void loop()
+{
+	cmri.process();
+	digitalWrite(13, cmri.get_bit(0));
+}

src/CMRI.cpp

@@ -39,7 +39,7 @@ CMRI::CMRI(unsigned int address, unsigned int input_bits, unsigned int output_bi
 
       // parsing state
       ,
-      _mode(PREAMBLE_1), _rx_index(0), _rx_data_len(0), _init_handler(nullptr)
+      _mode(PREAMBLE_1), _rx_index(0), _rx_data_len(0), _init_handler(nullptr), _transmit_delay_us(TRANSMIT_DELAY_US)
 
 {
 	// clear to zero
@@ -59,6 +59,11 @@ void CMRI::set_init_handler(void (*handler)(const uint8_t *, int))
 	_init_handler = handler;
 }
 
+void CMRI::set_transmit_delay(unsigned int delay_us)
+{
+	_transmit_delay_us = delay_us;
+}
+
 // reads in serial data, decodes packets
 // automatically responds to POLL requests
 // returns packet type so if we got a SET request you know to update your outputs
@@ -144,7 +149,7 @@ bool CMRI::set_byte(int pos, char b)
 
 void CMRI::transmit()
 {
-	delayMicroseconds(50); // a minscule delay to let things recover
+	delayMicroseconds(_transmit_delay_us);
 	_serial.write(255);
 	_serial.write(255);
 	_serial.write(STX);

src/CMRI.h

@@ -35,6 +35,7 @@ class CMRI
 	CMRI(unsigned int address = 0, unsigned int input_bits = 24, unsigned int output_bits = 48, Stream &serial_class = Serial);
 	void set_address(unsigned int address);
 	void set_init_handler(void (*handler)(const uint8_t *data, int len));
+	void set_transmit_delay(unsigned int delay_us);
 
 	bool process();
 	bool process_char(char c);
@@ -85,13 +86,21 @@ class CMRI
 	char *_tx_buffer;
 	int _rx_data_len;
 	void (*_init_handler)(const uint8_t *, int);
+	unsigned int _transmit_delay_us;
 
 	Stream &_serial;
 
 	// parsing state variables
 	int _mode;
 	int _rx_index;
 
+#ifndef TRANSMIT_DELAY_US
+// Default RS-485 turnaround delay (microseconds) before transmitting.
+// Modern hosts set dH/dL to zero; this is just for transceiver settling.
+// Override at compile time or use set_transmit_delay() at runtime.
+#define TRANSMIT_DELAY_US 50
+#endif
+
 	uint8_t _decode(uint8_t c); // process one character received from serial port
 };
 

test/test_cmri/test_main.cpp

@@ -194,6 +194,19 @@ void test_preamble_resync_after_garbage(void)
 	TEST_ASSERT_EQUAL_UINT8(CMRI::GET, s.tx[4]);
 }
 
+// set_transmit_delay overrides the default transmit delay.
+void test_set_transmit_delay(void)
+{
+	Stream s;
+	CMRI cmri(0, 24, 48, s);
+
+	cmri.set_byte(0, 0x42);
+	cmri.set_transmit_delay(100);
+	cmri.transmit();
+
+	TEST_ASSERT_EQUAL_UINT8(0x42, s.tx[5]);
+}
+
 int main(int, char **)
 {
 	UNITY_BEGIN();
@@ -205,6 +218,7 @@ int main(int, char **)
 	RUN_TEST(test_set_packet_updates_outputs);
 	RUN_TEST(test_address_filtering);
 	RUN_TEST(test_transmit_escapes_control_bytes);
+	RUN_TEST(test_set_transmit_delay);
 	RUN_TEST(test_preamble_resync_after_garbage);
 	return UNITY_END();
 }