Adding Wire (TWI/I2C) library from Wiring. Renamed TwoWire.cpp to Wire.cpp and Wire.h to Wire.cpp so that the #include in the sketch matches the name of the library.

targets/libraries/Wire/Wire.cpp

@@ -0,0 +1,262 @@
+/*
+  TwoWire.cpp - TWI/I2C library for Wiring & Arduino
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+extern "C" {
+  #include <stdlib.h>
+  #include <string.h>
+  #include <inttypes.h>
+  #include "twi.h"
+}
+
+#include "Wire.h"
+
+// Initialize Class Variables //////////////////////////////////////////////////
+
+uint8_t* TwoWire::rxBuffer = 0;
+uint8_t TwoWire::rxBufferIndex = 0;
+uint8_t TwoWire::rxBufferLength = 0;
+
+uint8_t TwoWire::txAddress = 0;
+uint8_t* TwoWire::txBuffer = 0;
+uint8_t TwoWire::txBufferIndex = 0;
+uint8_t TwoWire::txBufferLength = 0;
+
+uint8_t TwoWire::transmitting = 0;
+void (*TwoWire::user_onRequest)(void);
+void (*TwoWire::user_onReceive)(int);
+
+// Constructors ////////////////////////////////////////////////////////////////
+
+TwoWire::TwoWire()
+{
+}
+
+// Public Methods //////////////////////////////////////////////////////////////
+
+void TwoWire::begin(void)
+{
+  // init buffer for reads
+  rxBuffer = (uint8_t*) calloc(BUFFER_LENGTH, sizeof(uint8_t));
+  rxBufferIndex = 0;
+  rxBufferLength = 0;
+
+  // init buffer for writes
+  txBuffer = (uint8_t*) calloc(BUFFER_LENGTH, sizeof(uint8_t));
+  txBufferIndex = 0;
+  txBufferLength = 0;
+
+  twi_init();
+}
+
+void TwoWire::begin(uint8_t address)
+{
+  twi_setAddress(address);
+  twi_attachSlaveTxEvent(onRequestService);
+  twi_attachSlaveRxEvent(onReceiveService);
+  begin();
+}
+
+void TwoWire::begin(int address)
+{
+  begin((uint8_t)address);
+}
+
+void 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);
+  // set rx buffer iterator vars
+  rxBufferIndex = 0;
+  rxBufferLength = quantity;
+}
+
+void TwoWire::requestFrom(int address, int quantity)
+{
+  requestFrom((uint8_t)address, (uint8_t)quantity);
+}
+
+void TwoWire::beginTransmission(uint8_t address)
+{
+  // indicate that we are transmitting
+  transmitting = 1;
+  // set address of targeted slave
+  txAddress = address;
+  // reset tx buffer iterator vars
+  txBufferIndex = 0;
+  txBufferLength = 0;
+}
+
+void TwoWire::beginTransmission(int address)
+{
+  beginTransmission((uint8_t)address);
+}
+
+void TwoWire::endTransmission(void)
+{
+  // transmit buffer (blocking)
+  twi_writeTo(txAddress, txBuffer, txBufferLength, 1);
+  // reset tx buffer iterator vars
+  txBufferIndex = 0;
+  txBufferLength = 0;
+  // indicate that we are done transmitting
+  transmitting = 0;
+}
+
+// must be called in:
+// slave tx event callback
+// or after beginTransmission(address)
+void TwoWire::send(uint8_t data)
+{
+  if(transmitting){
+  // in master transmitter mode
+    // don't bother if buffer is full
+    if(txBufferLength >= BUFFER_LENGTH){
+      return;
+    }
+    // put byte in tx buffer
+    txBuffer[txBufferIndex] = data;
+    ++txBufferIndex;
+    // update amount in buffer   
+    txBufferLength = txBufferIndex;
+  }else{
+  // in slave send mode
+    // reply to master
+    twi_transmit(&data, 1);
+  }
+}
+
+// must be called in:
+// slave tx event callback
+// or after beginTransmission(address)
+void TwoWire::send(uint8_t* data, uint8_t quantity)
+{
+  if(transmitting){
+  // in master transmitter mode
+    for(uint8_t i = 0; i < quantity; ++i){
+      send(data[i]);
+    }
+  }else{
+  // in slave send mode
+    // reply to master
+    twi_transmit(data, quantity);
+  }
+}
+
+// must be called in:
+// slave tx event callback
+// or after beginTransmission(address)
+void TwoWire::send(char* data)
+{
+  send((uint8_t*)data, strlen(data));
+}
+
+// must be called in:
+// slave tx event callback
+// or after beginTransmission(address)
+void TwoWire::send(int data)
+{
+  send((uint8_t)data);
+}
+
+// must be called in:
+// slave rx event callback
+// or after requestFrom(address, numBytes)
+uint8_t TwoWire::available(void)
+{
+  return rxBufferLength - rxBufferIndex;
+}
+
+// must be called in:
+// slave rx event callback
+// or after requestFrom(address, numBytes)
+uint8_t TwoWire::receive(void)
+{
+  // default to returning null char
+  // for people using with char strings
+  uint8_t value = '\0';
+  
+  // get each successive byte on each call
+  if(rxBufferIndex < rxBufferLength){
+    value = rxBuffer[rxBufferIndex];
+    ++rxBufferIndex;
+  }
+
+  return value;
+}
+
+// behind the scenes function that is called when data is received
+void TwoWire::onReceiveService(uint8_t* inBytes, int numBytes)
+{
+  // don't bother if user hasn't registered a callback
+  if(!user_onReceive){
+    return;
+  }
+  // don't bother if rx buffer is in use by a master requestFrom() op
+  // i know this drops data, but it allows for slight stupidity
+  // meaning, they may not have read all the master requestFrom() data yet
+  if(rxBufferIndex < rxBufferLength){
+    return;
+  }
+  // copy twi rx buffer into local read buffer
+  // this enables new reads to happen in parallel
+  for(uint8_t i = 0; i < numBytes; ++i){
+    rxBuffer[i] = inBytes[i];    
+  }
+  // set rx iterator vars
+  rxBufferIndex = 0;
+  rxBufferLength = numBytes;
+  // alert user program
+  user_onReceive(numBytes);
+}
+
+// behind the scenes function that is called when data is requested
+void TwoWire::onRequestService(void)
+{
+  // don't bother if user hasn't registered a callback
+  if(!user_onRequest){
+    return;
+  }
+  // reset tx buffer iterator vars
+  // !!! this will kill any pending pre-master sendTo() activity
+  txBufferIndex = 0;
+  txBufferLength = 0;
+  // alert user program
+  user_onRequest();
+}
+
+// sets function called on slave write
+void TwoWire::onReceive( void (*function)(int) )
+{
+  user_onReceive = function;
+}
+
+// sets function called on slave read
+void TwoWire::onRequest( void (*function)(void) )
+{
+  user_onRequest = function;
+}
+
+// Preinstantiate Objects //////////////////////////////////////////////////////
+
+TwoWire Wire = TwoWire();
+

targets/libraries/Wire/Wire.h

@@ -0,0 +1,67 @@
+/*
+  TwoWire.h - TWI/I2C library for Arduino & Wiring
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef TwoWire_h
+#define TwoWire_h
+
+#include <inttypes.h>
+
+#define BUFFER_LENGTH 32
+
+class TwoWire
+{
+  private:
+    static uint8_t* rxBuffer;
+    static uint8_t rxBufferIndex;
+    static uint8_t rxBufferLength;
+
+    static uint8_t txAddress;
+    static uint8_t* txBuffer;
+    static uint8_t txBufferIndex;
+    static uint8_t txBufferLength;
+
+    static uint8_t transmitting;
+    static void (*user_onRequest)(void);
+    static void (*user_onReceive)(int);
+    static void onRequestService(void);
+    static void onReceiveService(uint8_t*, int);
+  public:
+    TwoWire();
+    void begin();
+    void begin(uint8_t);
+    void begin(int);
+    void beginTransmission(uint8_t);
+    void beginTransmission(int);
+    void endTransmission(void);
+    void requestFrom(uint8_t, uint8_t);
+    void requestFrom(int, int);
+    void send(uint8_t);
+    void send(uint8_t*, uint8_t);
+    void send(int);
+    void send(char*);
+    uint8_t available(void);
+    uint8_t receive(void);
+    void onReceive( void (*)(int) );
+    void onRequest( void (*)(void) );
+};
+
+extern TwoWire Wire;
+
+#endif
+

targets/libraries/Wire/examples/SFRRanger_reader/SFRRanger_reader.pde

@@ -0,0 +1,82 @@
+// I2C SRF10 or SRF08 Devantech Ultrasonic Ranger Finder 
+// by Nicholas Zambetti <http://www.zambetti.com>
+// and James Tichenor <http://www.jamestichenor.net> 
+
+// Demonstrates use of the Wire library reading data from the 
+// Devantech Utrasonic Rangers SFR08 and SFR10
+
+// Created 29 April 2006
+
+void setup()
+{
+  Wire.begin();                // join i2c bus (address optional for master)
+  Serial.begin(9600);          // start serial communication at 9600bps
+}
+
+int reading = 0;
+
+void loop()
+{
+  // step 1: instruct sensor to read echoes
+  Wire.beginTransmission(112); // transmit to device #112 (0x70)
+                               // the address specified in the datasheet is 224 (0xE0)
+                               // but i2c adressing uses the high 7 bits so it's 112
+  Wire.send(0x00);             // sets register pointer to the command register (0x00)  
+  Wire.send(0x50);             // command sensor to measure in "inches" (0x50) 
+                               // use 0x51 for centimeters
+                               // use 0x52 for ping microseconds
+  Wire.endTransmission();      // stop transmitting
+
+  // step 2: wait for readings to happen
+  delay(70);                   // datasheet suggests at least 65 milliseconds
+
+  // step 3: instruct sensor to return a particular echo reading
+  Wire.beginTransmission(112); // transmit to device #112
+  Wire.send(0x02);             // sets register pointer to echo #1 register (0x02)
+  Wire.endTransmission();      // stop transmitting
+
+  // step 4: request reading from sensor
+  Wire.requestFrom(112, 2);    // request 2 bytes from slave device #112
+
+  // step 5: receive reading from sensor
+  if(2 <= Wire.available())    // if two bytes were received
+  {
+    reading = Wire.receive();  // receive high byte (overwrites previous reading)
+    reading = reading << 8;    // shift high byte to be high 8 bits
+    reading |= Wire.receive(); // receive low byte as lower 8 bits
+    Serial.println(reading);   // print the reading
+  }
+
+  delay(250);                  // wait a bit since people have to read the output :)
+}
+
+
+/*
+
+// The following code changes the address of a Devantech Ultrasonic Range Finder (SRF10 or SRF08)
+// usage: changeAddress(0x70, 0xE6);
+
+void changeAddress(byte oldAddress, byte newAddress)
+{
+  Wire.beginTransmission(oldAddress);
+  Wire.send(0x00);
+  Wire.send(0xA0);
+  Wire.endTransmission();
+
+  Wire.beginTransmission(oldAddress);
+  Wire.send(0x00);
+  Wire.send(0xAA);
+  Wire.endTransmission();
+
+  Wire.beginTransmission(oldAddress);
+  Wire.send(0x00);
+  Wire.send(0xA5);
+  Wire.endTransmission();
+
+  Wire.beginTransmission(oldAddress);
+  Wire.send(0x00);
+  Wire.send(newAddress);
+  Wire.endTransmission();
+}
+
+*/

targets/libraries/Wire/examples/digital_potentiometer/digital_potentiometer.pde

@@ -0,0 +1,32 @@
+// I2C Digital Potentiometer
+// by Nicholas Zambetti <http://www.zambetti.com>
+// and Shawn Bonkowski <http://people.interaction-ivrea.it/s.bonkowski/>
+
+// Demonstrates use of the Wire library
+// Controls AD5171 digital potentiometer via I2C/TWI
+
+// Created 31 March 2006
+
+void setup()
+{
+  Wire.begin(); // join i2c bus (address optional for master)
+}
+
+byte val = 0;
+
+void loop()
+{
+  Wire.beginTransmission(44); // transmit to device #44 (0x2c)
+                              // device address is specified in datasheet
+  Wire.send(0x00);            // sends instruction byte  
+  Wire.send(val);             // sends potentiometer value byte  
+  Wire.endTransmission();     // stop transmitting
+
+  val++;        // increment value
+  if(val == 64) // if reached 64th position (max)
+  {
+    val = 0;    // start over from lowest value
+  }
+  delay(500);
+}
+

targets/libraries/Wire/examples/master_reader/master_reader.pde

@@ -0,0 +1,27 @@
+// Wire Master Reader
+// by Nicholas Zambetti <http://www.zambetti.com>
+
+// Demonstrates use of the Wire library
+// Reads data from an I2C/TWI slave device
+// Refer to the "Wire Slave Sender" example for use with this
+
+// Created 29 March 2006
+
+void setup()
+{
+  Wire.begin();        // join i2c bus (address optional for master)
+  Serial.begin(9600);  // start serial for output
+}
+
+void loop()
+{
+  Wire.requestFrom(2, 6);    // request 6 bytes from slave device #2
+
+  while(Wire.available())    // slave may send less than requested
+  { 
+    char c = Wire.receive(); // receive a byte as character
+    Serial.print(c);         // print the character
+  }
+
+  delay(500);
+}

targets/libraries/Wire/examples/master_writer/master_writer.pde

@@ -0,0 +1,26 @@
+// Wire Master Writer
+// by Nicholas Zambetti <http://www.zambetti.com>
+
+// Demonstrates use of the Wire library
+// Writes data to an I2C/TWI slave device
+// Refer to the "Wire Slave Receiver" example for use with this
+
+// Created 29 March 2006
+
+void setup()
+{
+  Wire.begin(); // join i2c bus (address optional for master)
+}
+
+byte x = 0;
+
+void loop()
+{
+  Wire.beginTransmission(4); // transmit to device #4
+  Wire.send("x is ");        // sends five bytes
+  Wire.send(x);              // sends one byte  
+  Wire.endTransmission();    // stop transmitting
+
+  x++;
+  delay(500);
+}

targets/libraries/Wire/examples/slave_receiver/slave_receiver.pde

@@ -0,0 +1,33 @@
+// Wire Slave Receiver
+// by Nicholas Zambetti <http://www.zambetti.com>
+
+// Demonstrates use of the Wire library
+// Receives data as an I2C/TWI slave device
+// Refer to the "Wire Master Writer" example for use with this
+
+// Created 29 March 2006
+
+void setup()
+{
+  Wire.begin(4);                // join i2c bus with address #4
+  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)
+{
+  while(1 < Wire.available()) // loop through all but the last
+  {
+    char c = Wire.receive(); // receive byte as a character
+    Serial.print(c);         // print the character
+  }
+  int x = Wire.receive();    // receive byte as an integer
+  Serial.println(x);         // print the integer
+}

targets/libraries/Wire/examples/slave_sender/slave_sender.pde

@@ -0,0 +1,27 @@
+// Wire Slave Sender
+// by Nicholas Zambetti <http://www.zambetti.com>
+
+// Demonstrates use of the Wire library
+// Sends data as an I2C/TWI slave device
+// Refer to the "Wire Master Reader" example for use with this
+
+// Created 29 March 2006
+
+void setup()
+{
+  Wire.begin(2);                // join i2c bus with address #2
+  Wire.onRequest(requestEvent); // register event
+}
+
+void loop()
+{
+  delay(100);
+}
+
+// function that executes whenever data is requested by master
+// this function is registered as an event, see setup()
+void requestEvent()
+{
+  Wire.send("hello "); // respond with message of 6 bytes
+                       // as expected by master
+}

targets/libraries/Wire/keywords.txt

@@ -0,0 +1,31 @@
+#######################################
+# Syntax Coloring Map For Wire
+#######################################
+
+#######################################
+# Datatypes (KEYWORD1)
+#######################################
+
+#######################################
+# Methods and Functions (KEYWORD2)
+#######################################
+
+begin	KEYWORD2
+beginTransmission	KEYWORD2
+endTransmission	KEYWORD2
+requestFrom	KEYWORD2
+send	KEYWORD2
+receive	KEYWORD2
+onReceive	KEYWORD2
+onRequest	KEYWORD2
+
+#######################################
+# Instances (KEYWORD2)
+#######################################
+
+Wire	KEYWORD2
+
+#######################################
+# Constants (LITERAL1)
+#######################################
+

targets/libraries/Wire/utility/twi.c

@@ -0,0 +1,448 @@
+/*
+  twi.c - TWI/I2C library for Wiring & Arduino
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include <math.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <compat/twi.h>
+
+#ifndef cbi
+#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
+#endif
+
+#ifndef sbi
+#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
+#endif
+
+#include "twi.h"
+
+static volatile uint8_t twi_state;
+static uint8_t twi_slarw;
+
+static void (*twi_onSlaveTransmit)(void);
+static void (*twi_onSlaveReceive)(uint8_t*, int);
+
+static uint8_t* twi_masterBuffer;
+static volatile uint8_t twi_masterBufferIndex;
+static uint8_t twi_masterBufferLength;
+
+static uint8_t* twi_txBuffer;
+static volatile uint8_t twi_txBufferIndex;
+static volatile uint8_t twi_txBufferLength;
+
+static uint8_t* twi_rxBuffer;
+static volatile uint8_t twi_rxBufferIndex;
+
+/* 
+ * Function twi_init
+ * Desc     readys twi pins and sets twi bitrate
+ * Input    none
+ * Output   none
+ */
+void twi_init(void)
+{
+  // initialize state
+  twi_state = TWI_READY;
+
+  #ifdef ATMEGA8
+    // activate internal pull-ups for twi
+    // as per note from atmega8 manual pg167
+    sbi(PORTC, 4);
+    sbi(PORTC, 5);
+  #else
+    // activate internal pull-ups for twi
+    // as per note from atmega128 manual pg204
+    sbi(PORTD, 0);
+    sbi(PORTD, 1);
+  #endif
+
+  // initialize twi prescaler and bit rate
+  cbi(TWSR, TWPS0);
+  cbi(TWSR, TWPS1);
+  TWBR = ((CPU_FREQ / TWI_FREQ) - 16) / 2;
+
+  /* twi bit rate formula from atmega128 manual pg 204
+  SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
+  note: TWBR should be 10 or higher for master mode
+  It is 72 for a 16mhz Wiring board with 100kHz TWI */
+
+  // enable twi module, acks, and twi interrupt
+	TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA);
+	
+	// allocate buffers
+  twi_masterBuffer = (uint8_t*) calloc(TWI_BUFFER_LENGTH, sizeof(uint8_t));
+  twi_txBuffer = (uint8_t*) calloc(TWI_BUFFER_LENGTH, sizeof(uint8_t));
+  twi_rxBuffer = (uint8_t*) calloc(TWI_BUFFER_LENGTH, sizeof(uint8_t));
+}
+
+/* 
+ * Function twi_slaveInit
+ * Desc     sets slave address and enables interrupt
+ * Input    none
+ * Output   none
+ */
+void twi_setAddress(uint8_t address)
+{
+  // set twi slave address (skip over TWGCE bit)
+  TWAR = address << 1;
+}
+
+/* 
+ * Function twi_readFrom
+ * Desc     attempts to become twi bus master and read a
+ *          series of bytes from a device on the bus
+ * 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
+ */
+uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
+{
+  uint8_t i;
+
+  // ensure data will fit into buffer
+  if(TWI_BUFFER_LENGTH < length){
+    return 1;
+  }
+
+  // wait until twi is ready, become master receiver
+  while(TWI_READY != twi_state){
+    continue;
+  }
+  twi_state = TWI_MRX;
+
+  // initialize buffer iteration vars
+  twi_masterBufferIndex = 0;
+  twi_masterBufferLength = length;
+
+  // build sla+w, slave device address + w bit
+  twi_slarw = TW_READ;
+	twi_slarw |= address << 1;
+
+  // send start condition
+	TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
+
+	// wait for read operation to complete
+	while(TWI_MRX == twi_state){
+	  continue;
+	}
+
+  // copy twi buffer to data
+  for(i = 0; i < length; ++i){
+    data[i] = twi_masterBuffer[i];
+  }
+	
+	return 0;
+}
+
+/* 
+ * Function twi_writeTo
+ * Desc     attempts to become twi bus master and write a
+ *          series of bytes to a device on the bus
+ * Input    address: 7bit i2c device address
+ *          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
+ */
+uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait)
+{
+  uint8_t i;
+
+  // ensure data will fit into buffer
+  if(TWI_BUFFER_LENGTH < length){
+    return 1;
+  }
+
+  // wait until twi is ready, become master transmitter
+  while(TWI_READY != twi_state){
+    continue;
+  }
+  twi_state = TWI_MTX;
+
+  // initialize buffer iteration vars
+  twi_masterBufferIndex = 0;
+  twi_masterBufferLength = length;
+  
+  // copy data to twi buffer
+  for(i = 0; i < length; ++i){
+    twi_masterBuffer[i] = data[i];
+  }
+  
+  // build sla+w, slave device address + w bit
+  twi_slarw = TW_WRITE;
+	twi_slarw |= address << 1;
+  
+  // send start condition
+	TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
+
+	// wait for write operation to complete
+	while(wait && (TWI_MTX == twi_state)){
+	  continue;
+	}
+	
+	return 0;
+}
+
+/* 
+ * Function twi_transmit
+ * Desc     fills slave tx buffer with data
+ *          must be called in slave tx event callback
+ * Input    data: pointer to byte array
+ *          length: number of bytes in array
+ * Output   1 length too long for buffer
+ *          2 not slave transmitter
+ *          0 ok
+ */
+uint8_t twi_transmit(uint8_t* data, uint8_t length)
+{
+  uint8_t i;
+
+  // ensure data will fit into buffer
+  if(TWI_BUFFER_LENGTH < length){
+    return 1;
+  }
+  
+  // ensure we are currently a slave transmitter
+  if(TWI_STX != twi_state){
+    return 2;
+  }
+  
+  // set length and copy data into tx buffer
+  twi_txBufferLength = length;
+  for(i = 0; i < length; ++i){
+    twi_txBuffer[i] = data[i];
+  }
+  
+  return 0;
+}
+
+/* 
+ * Function twi_attachSlaveRxEvent
+ * Desc     sets function called before a slave read operation
+ * Input    function: callback function to use
+ * Output   none
+ */
+void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) )
+{
+  twi_onSlaveReceive = function;
+}
+
+/* 
+ * Function twi_attachSlaveTxEvent
+ * Desc     sets function called before a slave write operation
+ * Input    function: callback function to use
+ * Output   none
+ */
+void twi_attachSlaveTxEvent( void (*function)(void) )
+{
+  twi_onSlaveTransmit = function;
+}
+
+/* 
+ * Function twi_reply
+ * Desc     sends byte or readys receive line
+ * Input    ack: byte indicating to ack or to nack
+ * Output   none
+ */
+void twi_reply(uint8_t ack)
+{
+	// transmit master read ready signal, with or without ack
+	if(ack){
+	  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA);
+  }else{
+	  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT);
+  }
+}
+
+/* 
+ * Function twi_stop
+ * Desc     relinquishes bus master status
+ * Input    none
+ * Output   none
+ */
+void twi_stop(void)
+{
+  // send stop condition
+  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO);
+
+  // wait for stop condition to be exectued on bus
+  // TWINT is not set after a stop condition!
+  while(TWCR & _BV(TWSTO)){
+    continue;
+  }
+
+  // update twi state
+  twi_state = TWI_READY;
+}
+
+/* 
+ * Function twi_releaseBus
+ * Desc     releases bus control
+ * Input    none
+ * Output   none
+ */
+void twi_releaseBus(void)
+{
+  // release bus
+  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT);
+
+  // update twi state
+  twi_state = TWI_READY;
+}
+
+SIGNAL(SIG_2WIRE_SERIAL)
+{
+  switch(TW_STATUS){
+    // All Master
+    case TW_START:     // sent start condition
+    case TW_REP_START: // sent repeated start condition
+      // copy device address and r/w bit to output register and ack
+      TWDR = twi_slarw;
+      twi_reply(1);
+      break;
+
+    // Master Transmitter
+    case TW_MT_SLA_ACK:  // slave receiver acked address
+    case TW_MT_DATA_ACK: // slave receiver acked data
+      // if there is data to send, send it, otherwise stop 
+      if(twi_masterBufferIndex < twi_masterBufferLength){
+        // copy data to output register and ack
+        TWDR = twi_masterBuffer[twi_masterBufferIndex++];
+        twi_reply(1);
+      }else{
+        twi_stop();
+      }
+      break;
+    case TW_MT_SLA_NACK:  // address sent, nack received
+    case TW_MT_DATA_NACK: // data sent, nack received
+      twi_stop();
+      break;
+    case TW_MT_ARB_LOST: // lost bus arbitration
+      twi_releaseBus();
+      break;
+
+    // Master Receiver
+    case TW_MR_DATA_ACK: // data received, ack sent
+      // put byte into buffer
+      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
+    case TW_MR_SLA_ACK:  // address sent, ack received
+      // ack if more bytes are expected, otherwise nack
+      if(twi_masterBufferIndex < twi_masterBufferLength){
+        twi_reply(1);
+      }else{
+        twi_reply(0);
+      }
+      break;
+    case TW_MR_DATA_NACK: // data received, nack sent
+      // put final byte into buffer
+      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
+    case TW_MR_SLA_NACK: // address sent, nack received
+      twi_stop();
+      break;
+    // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case
+
+    // Slave Receiver
+    case TW_SR_SLA_ACK:   // addressed, returned ack
+    case TW_SR_GCALL_ACK: // addressed generally, returned ack
+    case TW_SR_ARB_LOST_SLA_ACK:   // lost arbitration, returned ack
+    case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack
+      // enter slave receiver mode
+      twi_state = TWI_SRX;
+      // indicate that rx buffer can be overwritten and ack
+      twi_rxBufferIndex = 0;
+      twi_reply(1);
+      break;
+    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){
+        // put byte in buffer and ack
+        twi_rxBuffer[twi_rxBufferIndex++] = TWDR;
+        twi_reply(1);
+      }else{
+        // otherwise nack
+        twi_reply(0);
+      }
+      break;
+    case TW_SR_STOP: // stop or repeated start condition received
+      // put a null char after data if there's room
+      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
+        twi_rxBuffer[twi_rxBufferIndex] = '\0';
+      }
+      // callback to user defined callback
+      twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex);
+      // ack future responses
+      twi_reply(1);
+      // leave slave receiver state
+      twi_state = TWI_READY;
+      break;
+    case TW_SR_DATA_NACK:       // data received, returned nack
+    case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack
+      // nack back at master
+      twi_reply(0);
+      break;
+    
+    // Slave Transmitter
+    case TW_ST_SLA_ACK:          // addressed, returned ack
+    case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack
+      // enter slave transmitter mode
+      twi_state = TWI_STX;
+      // ready the tx buffer index for iteration
+      twi_txBufferIndex = 0;
+      // set tx buffer length to be zero, to verify if user changes it
+      twi_txBufferLength = 0;
+      // request for txBuffer to be filled and length to be set
+      // note: user must call twi_transmit(bytes, length) to do this
+      twi_onSlaveTransmit();
+      // if they didn't change buffer & length, initialize it
+      if(0 == twi_txBufferLength){
+        twi_txBufferLength = 1;
+        twi_txBuffer[0] = 0x00;
+      }
+      // transmit first byte from buffer, fall
+    case TW_ST_DATA_ACK: // byte sent, ack returned
+      // copy data to output register
+      TWDR = twi_txBuffer[twi_txBufferIndex++];
+      // if there is more to send, ack, otherwise nack
+      if(twi_txBufferIndex < twi_txBufferLength){
+        twi_reply(1);
+      }else{
+        twi_reply(0);
+      }
+      break;
+    case TW_ST_DATA_NACK: // received nack, we are done 
+    case TW_ST_LAST_DATA: // received ack, but we are done already!
+      // ack future responses
+      twi_reply(1);
+      // leave slave receiver state
+      twi_state = TWI_READY;
+      break;
+
+    // All
+    case TW_NO_INFO:   // no state information
+      break;
+    case TW_BUS_ERROR: // bus error, illegal stop/start
+      twi_stop();
+      break;
+  }
+}
+

targets/libraries/Wire/utility/twi.h

@@ -0,0 +1,57 @@
+/*
+  twi.h - TWI/I2C library for Wiring & Arduino
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef twi_h
+#define twi_h
+
+  #include <inttypes.h>
+
+  //#define ATMEGA8
+
+  #ifndef CPU_FREQ
+  #define CPU_FREQ 16000000L
+  #endif
+
+  #ifndef TWI_FREQ
+  #define TWI_FREQ 100000L
+  #endif
+
+  #ifndef TWI_BUFFER_LENGTH
+  #define TWI_BUFFER_LENGTH 32
+  #endif
+
+  #define TWI_READY 0
+  #define TWI_MRX   1
+  #define TWI_MTX   2
+  #define TWI_SRX   3
+  #define TWI_STX   4
+  
+  void twi_init(void);
+  void twi_setAddress(uint8_t);
+  uint8_t twi_readFrom(uint8_t, uint8_t*, uint8_t);
+  uint8_t twi_writeTo(uint8_t, uint8_t*, uint8_t, uint8_t);
+  uint8_t twi_transmit(uint8_t*, uint8_t);
+  void twi_attachSlaveRxEvent( void (*)(uint8_t*, int) );
+  void twi_attachSlaveTxEvent( void (*)(void) );
+  void twi_reply(uint8_t);
+  void twi_stop(void);
+  void twi_releaseBus(void);
+
+#endif
+