I2C/Wire library: changes for issue #42

libraries/Wire/src/Wire.cpp

@@ -86,6 +86,11 @@ void TwoWire::setClock(uint32_t clock)
   twi_setFrequency(clock);
 }
 
+void TwoWire::setTimeoutInMicros(uint16_t timeout)
+{
+  twi_setTimeoutInMicros(timeout);
+}
+
 uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint32_t iaddress, uint8_t isize, uint8_t sendStop)
 {
   if (isize > 0) {

libraries/Wire/src/Wire.h

@@ -54,6 +54,7 @@ class TwoWire : public Stream
     void begin(int);
     void end();
     void setClock(uint32_t);
+    void setTimeoutInMicros(uint16_t);
     void beginTransmission(uint8_t);
     void beginTransmission(int);
     uint8_t endTransmission(void);

libraries/Wire/src/utility/twi.c

@@ -25,7 +25,7 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <compat/twi.h>
-#include "Arduino.h" // for digitalWrite
+#include "Arduino.h" // for digitalWrite and micros
 
 #ifndef cbi
 #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
@@ -42,6 +42,7 @@ static volatile uint8_t twi_state;
 static volatile uint8_t twi_slarw;
 static volatile uint8_t twi_sendStop;			// should the transaction end with a stop
 static volatile uint8_t twi_inRepStart;			// in the middle of a repeated start
+static volatile uint16_t twi_timeout_us = 0;
 
 static void (*twi_onSlaveTransmit)(void);
 static void (*twi_onSlaveReceive)(uint8_t*, int);
@@ -154,7 +155,12 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sen
   }
 
   // wait until twi is ready, become master receiver
+  uint32_t startMicros = micros();
   while(TWI_READY != twi_state){
+    if((twi_timeout_us > 0) && (micros() - startMicros > twi_timeout_us)) {
+      twi_handleTimeout();
+      return 0;
+    }
     continue;
   }
   twi_state = TWI_MRX;
@@ -193,7 +199,12 @@ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sen
     TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
 
   // wait for read operation to complete
+  startMicros = micros();
   while(TWI_MRX == twi_state){
+    if((twi_timeout_us > 0) && (micros() - startMicros > twi_timeout_us)) {
+      twi_handleTimeout();
+      return 0;
+    }
     continue;
   }
 
@@ -233,7 +244,12 @@ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait
   }
 
   // wait until twi is ready, become master transmitter
+  uint32_t startMicros = micros();
   while(TWI_READY != twi_state){
+    if((twi_timeout_us > 0) && (micros() - startMicros > twi_timeout_us)) {
+      twi_handleTimeout();
+      return 4;
+    }
     continue;
   }
   twi_state = TWI_MTX;
@@ -275,7 +291,12 @@ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait
     TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE) | _BV(TWSTA);	// enable INTs
 
   // wait for write operation to complete
+  startMicros = micros();
   while(wait && (TWI_MTX == twi_state)){
+    if((twi_timeout_us > 0) && (micros() - startMicros > twi_timeout_us)) {
+      twi_handleTimeout();
+      return 4;
+    }
     continue;
   }
 
@@ -373,7 +394,14 @@ void twi_stop(void)
 
   // wait for stop condition to be exectued on bus
   // TWINT is not set after a stop condition!
+  uint32_t counter = 0;
   while(TWCR & _BV(TWSTO)){
+    counter++;
+    if((twi_timeout_us > 0) && (counter >= 25000)) {
+      twi_handleTimeout();
+      return;
+    }
+
     continue;
   }
 
@@ -396,6 +424,40 @@ void twi_releaseBus(void)
   twi_state = TWI_READY;
 }
 
+/* 
+ * Function twi_setTimeoutInMicros
+ * Desc     set a global timeout for while loops that we might get stuck in
+ * Input    timeout value in microseconds
+ * Output   none
+ */
+void twi_setTimeoutInMicros(uint16_t timeout)
+{
+  twi_timeout_us = timeout;
+}
+
+/* 
+ * Function twi_handleTimeout
+ * Desc     do this stuff when a while loop here has run for longer than twi_timeout_us microseconds
+ * Input    none
+ * Output   none
+ */
+void twi_handleTimeout(void)
+{
+  // remember the bitrate register value
+  uint8_t previous_TWBR = TWBR;
+
+  // remember the address register value
+  uint8_t previous_TWAR = TWBR;
+
+  // reset the interface
+  twi_disable();
+  twi_init();
+
+  // reapply the previous register values
+  TWAR = previous_TWAR;
+  TWBR = previous_TWAR;
+}
+
 ISR(TWI_vect)
 {
   switch(TW_STATUS){

libraries/Wire/src/utility/twi.h

@@ -50,6 +50,8 @@
   void twi_reply(uint8_t);
   void twi_stop(void);
   void twi_releaseBus(void);
+  void twi_setTimeoutInMicros(uint16_t);
+  void twi_handleTimeout(void);
 
 #endif