Wire library patch to provide better error handling.

hardware/libraries/Wire/Wire.cpp

@@ -77,22 +77,24 @@ void TwoWire::begin(int address)
   begin((uint8_t)address);
 }
 
-void TwoWire::requestFrom(uint8_t address, uint8_t quantity)
+uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity)
 {
   // clamp to buffer length
   if(quantity > BUFFER_LENGTH){
     quantity = BUFFER_LENGTH;
   }
   // perform blocking read into buffer
-  twi_readFrom(address, rxBuffer, quantity);
+  uint8_t read = twi_readFrom(address, rxBuffer, quantity);
   // set rx buffer iterator vars
   rxBufferIndex = 0;
-  rxBufferLength = quantity;
+  rxBufferLength = read;
+
+  return read;
 }
 
-void TwoWire::requestFrom(int address, int quantity)
+uint8_t TwoWire::requestFrom(int address, int quantity)
 {
-  requestFrom((uint8_t)address, (uint8_t)quantity);
+  return requestFrom((uint8_t)address, (uint8_t)quantity);
 }
 
 void TwoWire::beginTransmission(uint8_t address)
@@ -111,15 +113,16 @@ void TwoWire::beginTransmission(int address)
   beginTransmission((uint8_t)address);
 }
 
-void TwoWire::endTransmission(void)
+uint8_t TwoWire::endTransmission(void)
 {
   // transmit buffer (blocking)
-  twi_writeTo(txAddress, txBuffer, txBufferLength, 1);
+  int8_t ret = twi_writeTo(txAddress, txBuffer, txBufferLength, 1);
   // reset tx buffer iterator vars
   txBufferIndex = 0;
   txBufferLength = 0;
   // indicate that we are done transmitting
   transmitting = 0;
+  return ret;
 }
 
 // must be called in:

hardware/libraries/Wire/Wire.h

@@ -48,9 +48,9 @@ class TwoWire
     void begin(int);
     void beginTransmission(uint8_t);
     void beginTransmission(int);
-    void endTransmission(void);
-    void requestFrom(uint8_t, uint8_t);
-    void requestFrom(int, int);
+    uint8_t endTransmission(void);
+    uint8_t requestFrom(uint8_t, uint8_t);
+    uint8_t requestFrom(int, int);
     void send(uint8_t);
     void send(uint8_t*, uint8_t);
     void send(int);

hardware/libraries/Wire/utility/twi.c

@@ -51,6 +51,8 @@ static volatile uint8_t twi_txBufferLength;
 static uint8_t* twi_rxBuffer;
 static volatile uint8_t twi_rxBufferIndex;
 
+static volatile uint8_t twi_error;
+
 /* 
  * Function twi_init
  * Desc     readys twi pins and sets twi bitrate
@@ -112,7 +114,7 @@ void twi_setAddress(uint8_t address)
  * Input    address: 7bit i2c device address
  *          data: pointer to byte array
  *          length: number of bytes to read into array
- * Output   byte: 0 ok, 1 length too long for buffer
+ * Output   number of bytes read
  */
 uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
 {
@@ -120,7 +122,7 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
 
   // ensure data will fit into buffer
   if(TWI_BUFFER_LENGTH < length){
-    return 1;
+    return 0;
   }
 
   // wait until twi is ready, become master receiver
@@ -128,6 +130,8 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
     continue;
   }
   twi_state = TWI_MRX;
+  // reset error state (0xFF.. no error occured)
+  twi_error = 0xFF;
 
   // initialize buffer iteration vars
   twi_masterBufferIndex = 0;
@@ -145,12 +149,15 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
 	  continue;
 	}
 
+  if (twi_masterBufferIndex < length)
+	length = twi_masterBufferIndex;
+
   // copy twi buffer to data
   for(i = 0; i < length; ++i){
     data[i] = twi_masterBuffer[i];
   }
 	
-	return 0;
+	return length;
 }
 
 /* 
@@ -161,7 +168,11 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
  *          data: pointer to byte array
  *          length: number of bytes in array
  *          wait: boolean indicating to wait for write or not
- * Output   byte: 0 ok, 1 length too long for buffer
+ * Output   0 .. success
+ *          1 .. length to long for buffer
+ *          2 .. address send, NACK received
+ *          3 .. data send, NACK received
+ *          4 .. other twi error (lost bus arbitration, bus error, ..)
  */
 uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait)
 {
@@ -177,6 +188,8 @@ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait
     continue;
   }
   twi_state = TWI_MTX;
+  // reset error state (0xFF.. no error occured)
+  twi_error = 0xFF;
 
   // initialize buffer iteration vars
   twi_masterBufferIndex = 0;
@@ -199,7 +212,14 @@ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait
 	  continue;
 	}
 	
-	return 0;
+	if (twi_error == 0xFF)
+		return 0;	// success
+	else if (twi_error == TW_MT_SLA_NACK)
+		return 2;	// error: address send, nack received
+	else if (twi_error == TW_MT_DATA_NACK)
+		return 3;	// error: data send, nack received
+	else
+		return 4;	// other twi error
 }
 
 /* 
@@ -333,10 +353,15 @@ SIGNAL(SIG_2WIRE_SERIAL)
       }
       break;
     case TW_MT_SLA_NACK:  // address sent, nack received
+      twi_error = TW_MT_SLA_NACK;
+      twi_stop();
+      break;
     case TW_MT_DATA_NACK: // data sent, nack received
+      twi_error = TW_MT_DATA_NACK;
       twi_stop();
       break;
     case TW_MT_ARB_LOST: // lost bus arbitration
+      twi_error = TW_MT_ARB_LOST;
       twi_releaseBus();
       break;
 
@@ -441,6 +466,7 @@ SIGNAL(SIG_2WIRE_SERIAL)
     case TW_NO_INFO:   // no state information
       break;
     case TW_BUS_ERROR: // bus error, illegal stop/start
+      twi_error = TW_BUS_ERROR;
       twi_stop();
       break;
   }

hardware/libraries/Wire/utility/twi.h

@@ -17,18 +17,18 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
-#ifndef twi_h
-#define twi_h
+#ifndef twi_h
+#define twi_h
 
   #include <inttypes.h>
 
   //#define ATMEGA8
 
-  #ifndef CPU_FREQ
+  #ifndef CPU_FREQ
   #define CPU_FREQ 16000000L
   #endif
 
-  #ifndef TWI_FREQ
+  #ifndef TWI_FREQ
   #define TWI_FREQ 100000L
   #endif
 
@@ -51,7 +51,7 @@
   void twi_attachSlaveTxEvent( void (*)(void) );
   void twi_reply(uint8_t);
   void twi_stop(void);
-  void twi_releaseBus(void);
-
+  void twi_releaseBus(void);
+
 #endif