basic implementation of DS18B20 emulation

OneWireIO.ino

@@ -9,13 +9,30 @@ Pin oneWireData(2);
 Pin led(13);
 
 // This is the ROM the arduino will respond to, make sure it doesn't conflict with another device
-const byte owROM[7] = { 0xE2, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02 };
+const byte owROM[7] = { 0x28, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02 };
 
-const byte acknowledge = 0x42;
+// This sample emulates a DS18B20 device (temperature sensor), so we start by defining the available commands
+const byte DS18B20_START_CONVERSION = 0x44;
+const byte DS18B20_READ_SCRATCHPAD = 0xBE;
+const byte DS18B20_WRITE_SCRATCHPAD = 0x4E;
 
-// This sample implements a simple protocol : sending match ROM, then the ROM, then 0x01 will turn the arduino light on. Sending 0x02 will turn it off. In each case, the byte 0x42 is sent as acknowledgement.
-const byte CMD_TurnOn = 0x01;
-const byte CMD_TurnOff = 0x02;
+// TODO:
+// - handle configuration (resolution, alarms)
+// - send 0 bits while conversion is in progress, 1 bits when it's done (until reset)
+
+enum DeviceState
+{
+	DS_WaitingReset,
+	DS_WaitingCommand,
+	DS_ConvertingTemperature,
+	DS_TemperatureConverted,
+};
+volatile DeviceState state = DS_WaitingReset;
+
+// scratchpad, with the CRC byte at the end
+volatile byte scratchpad[9];
+
+volatile unsigned long conversionStartTime = 0;
 
 // This function will be called each time the OneWire library has an event to notify (reset, error, byte received)
 void owReceive(OneWireSlave::ReceiveEvent evt, byte data);
@@ -32,14 +49,32 @@ void setup()
 
 void loop()
 {
-	delay(1);
-
-	// You can do anything you want here, the OneWire library works entirely in background, using interrupts.
+	delay(10);
 
 	cli();//disable interrupts
 	// Be sure to not block interrupts for too long, OneWire timing is very tight for some operations. 1 or 2 microseconds (yes, microseconds, not milliseconds) can be too much depending on your master controller, but then it's equally unlikely that you block exactly at the moment where it matters.
 	// This can be mitigated by using error checking and retry in your high-level communication protocol. A good thing to do anyway.
+	DeviceState localState = state;
+	unsigned long localConversionStartTime = conversionStartTime;
 	sei();//enable interrupts
+
+	if (localState == DS_ConvertingTemperature && millis() > localConversionStartTime + 750)
+	{
+		float temperature = 42.0f; // here you could plug any logic you want to return the emulated temperature
+		int16_t raw = (int16_t)(temperature * 16.0f + 0.5f);
+
+		byte data[9];
+		data[0] = (byte)raw;
+		data[1] = (byte)(raw >> 8);
+		for (int i = 2; i < 8; ++i)
+			data[i] = 0;
+		data[8] = OWSlave.crc8(data, 8);
+
+		cli();
+		memcpy((void*)scratchpad, data, 9);
+		state = DS_TemperatureConverted;
+		sei();
+	}
 }
 
 void owReceive(OneWireSlave::ReceiveEvent evt, byte data)
@@ -47,27 +82,35 @@ void owReceive(OneWireSlave::ReceiveEvent evt, byte data)
 	switch (evt)
 	{
 	case OneWireSlave::RE_Byte:
-		if (data == CMD_TurnOn)
+		switch (state)
 		{
-			led.writeHigh();
-		}
-		else if (data == CMD_TurnOff)
+		case DS_WaitingCommand:
+			switch (data)
 			{
-			led.writeLow();
+			case DS18B20_START_CONVERSION:
+				state = DS_ConvertingTemperature;
+				conversionStartTime = millis();
+				break;
+
+			case DS18B20_READ_SCRATCHPAD:
+				state = DS_WaitingReset;
+				OWSlave.write((const byte*)scratchpad, 9, 0);
+				break;
+
+			case DS18B20_WRITE_SCRATCHPAD:
+				
+				break;
 			}
-		else
-		{
 			break;
 		}
+		break;
 
-		// in this simple example we just reply with one byte to say we've processed the command
-		// a real application should have a CRC system to ensure messages are not corrupt, for both directions
-		// you can use the static OneWireSlave::crc8 method to add CRC checks in your communication protocol (it conforms to standard one-wire CRC checks, that is used to compute the ROM last byte for example)
-		OWSlave.write(&acknowledge, 1, NULL);
-
+	case OneWireSlave::RE_Reset:
+		state = DS_WaitingCommand;
 		break;
 
-	default:
-		; // we could also react to reset and error notifications, but not in this sample
+	case OneWireSlave::RE_Error:
+		state = DS_WaitingReset;
+		break;
 	}
 }