fix bug #1354: I2C/TWI Library: Buffer Overflow

[neophob]

If we send i2c data larger than the arduino buffer (default: 32bytes) the arduino waits infinitely in a while loop (freeze). This fixes this.

[matthijskooijman]

I'm not sure if this is the proper fix for this issue, it might have side effects or leave different aspects of this issue unfixed. Now that I know this patch fixes the issue, I'm sure I've identified the cause of the issue and I'll have a closer look next week.

[neophob]

matthijs, do you have a proper fix for this issue?

[matthijskooijman]

I have been distracted by some fixes in the HardwareSerial driver, so I haven't actually worked on this one yet. It's still on my todolist, though, so I'll get back to you (probably not until next week though).

[neophob]

Any news about this issue?

[netguy204]

I've encountered this bug as well and would love to see this merged.

[sandeepmistry]

@cmaglie this looks good to merge to me. It will resolve https://github.com/arduino/Arduino/issues/486 as well.

I've tested with a Uno to Uno Wire setup by artificially lowering the slave RX buffer size:

diff --git a/hardware/arduino/avr/libraries/Wire/utility/twi.c b/hardware/arduino/avr/libraries/Wire/utility/twi.c
index b436e69..600103a 100644
--- a/hardware/arduino/avr/libraries/Wire/utility/twi.c
+++ b/hardware/arduino/avr/libraries/Wire/utility/twi.c
@@ -466,7 +466,7 @@ ISR(TWI_vect)
     case TW_SR_DATA_ACK:       // data received, returned ack
     case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack
       // if there is still room in the rx buffer
-      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
+      if(twi_rxBufferIndex < 10){
         // put byte in buffer and ack
         twi_rxBuffer[twi_rxBufferIndex++] = TWDR;
         twi_reply(1);

and the following sketches:

Master (modified version of master_writer example):

#include <Wire.h>

void setup() {
  Serial.begin(9600);
  Wire.begin(); // join i2c bus (address optional for master)
}

void loop() {
  Wire.beginTransmission(8); // transmit to device #8
  Wire.write("fedcba9876543210");
  Serial.println(Wire.endTransmission(), HEX);    // stop transmitting

  delay(500);

  Wire.beginTransmission(8); // transmit to device #8
  Wire.write("0123456789");
  Serial.println(Wire.endTransmission(), HEX);

  delay(500);
}

Slave (modified version of slave_receiver example):

#include <Wire.h>

void setup() {
  Wire.begin(8);                // join i2c bus with address #8
  Wire.onReceive(receiveEvent); // register event
  Serial.begin(9600);           // start serial for output
}

void loop() {
  delay(100);
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany) {
  Serial.println(howMany);
  while (Wire.available()) {
    char c = Wire.read();
    Serial.print(c);
  }

  Serial.println();
}

Output of master sketch alternates between 0 and 3 (success and data send, NACK received).

[CLAassistant]

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