From 79904311bb35ca52b51650f834683606e31882c2 Mon Sep 17 00:00:00 2001
From: "David A. Mellis" <d.mellis@arduino.cc>
Date: Sat, 21 Jun 2008 23:16:27 +0000
Subject: Wire library patch to provide better error handling.

---
 libraries/Wire/utility/twi.c | 36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

(limited to 'libraries/Wire/utility/twi.c')

diff --git a/libraries/Wire/utility/twi.c b/libraries/Wire/utility/twi.c
index 563b41b..3e5489f 100644
--- a/libraries/Wire/utility/twi.c
+++ b/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;
   }
-- 
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