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/*
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  twi.c - TWI/I2C library for Wiring & Arduino
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  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
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  This library is free software; you can redistribute it and/or
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  modify it under the terms of the GNU Lesser General Public
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  License as published by the Free Software Foundation; either
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  version 2.1 of the License, or (at your option) any later version.
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  This library is distributed in the hope that it will be useful,
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  but WITHOUT ANY WARRANTY; without even the implied warranty of
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  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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  Lesser General Public License for more details.
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  You should have received a copy of the GNU Lesser General Public
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  License along with this library; if not, write to the Free Software
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  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
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*/
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#include <math.h>
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#include <stdlib.h>
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#include <inttypes.h>
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <compat/twi.h>
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#ifndef cbi
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#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
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#endif
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#ifndef sbi
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#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
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#endif
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#include "twi.h"
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static volatile uint8_t twi_state;
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static uint8_t twi_slarw;
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static void (*twi_onSlaveTransmit)(void);
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static void (*twi_onSlaveReceive)(uint8_t*, int);
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static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH];
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static volatile uint8_t twi_masterBufferIndex;
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static uint8_t twi_masterBufferLength;
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static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH];
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static volatile uint8_t twi_txBufferIndex;
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static volatile uint8_t twi_txBufferLength;
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static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH];
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static volatile uint8_t twi_rxBufferIndex;
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static volatile uint8_t twi_error;
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/* 
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 * Function twi_init
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 * Desc     readys twi pins and sets twi bitrate
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 * Input    none
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 * Output   none
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 */
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void twi_init(void)
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{
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  // initialize state
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  twi_state = TWI_READY;
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  // activate internal pullups for twi.
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  //digitalWrite(SDA, 1);
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  //digitalWrite(SCL, 1);
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  // initialize twi prescaler and bit rate
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  cbi(TWSR, TWPS0);
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  cbi(TWSR, TWPS1);
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  TWBR = ((F_CPU / TWI_FREQ) - 16) / 2;
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  /* twi bit rate formula from atmega128 manual pg 204
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  SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
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  note: TWBR should be 10 or higher for master mode
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  It is 72 for a 16mhz Wiring board with 100kHz TWI */
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  // enable twi module, acks, and twi interrupt
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  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA);
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}
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/* 
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 * Function twi_slaveInit
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 * Desc     sets slave address and enables interrupt
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 * Input    none
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 * Output   none
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 */
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void twi_setAddress(uint8_t address)
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{
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  // set twi slave address (skip over TWGCE bit)
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  TWAR = address << 1;
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}
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/* 
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 * Function twi_readFrom
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 * Desc     attempts to become twi bus master and read a
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 *          series of bytes from a device on the bus
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 * Input    address: 7bit i2c device address
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 *          data: pointer to byte array
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 *          length: number of bytes to read into array
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 * Output   number of bytes read
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 */
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uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length)
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{
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  uint8_t i;
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  // ensure data will fit into buffer
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  if(TWI_BUFFER_LENGTH < length){
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    return 0;
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  }
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  // wait until twi is ready, become master receiver
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  while(TWI_READY != twi_state){
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    continue;
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  }
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  twi_state = TWI_MRX;
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  // reset error state (0xFF.. no error occured)
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  twi_error = 0xFF;
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  // initialize buffer iteration vars
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  twi_masterBufferIndex = 0;
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  twi_masterBufferLength = length-1;  // This is not intuitive, read on...
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  // On receive, the previously configured ACK/NACK setting is transmitted in
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  // response to the received byte before the interrupt is signalled. 
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  // Therefor we must actually set NACK when the _next_ to last byte is
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  // received, causing that NACK to be sent in response to receiving the last
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  // expected byte of data.
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  // build sla+w, slave device address + w bit
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  twi_slarw = TW_READ;
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  twi_slarw |= address << 1;
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  // send start condition
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  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
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  // wait for read operation to complete
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  while(TWI_MRX == twi_state){
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    continue;
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  }
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  if (twi_masterBufferIndex < length)
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    length = twi_masterBufferIndex;
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  // copy twi buffer to data
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  for(i = 0; i < length; ++i){
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    data[i] = twi_masterBuffer[i];
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  }
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  return length;
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}
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/* 
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 * Function twi_writeTo
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 * Desc     attempts to become twi bus master and write a
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 *          series of bytes to a device on the bus
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 * Input    address: 7bit i2c device address
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 *          data: pointer to byte array
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 *          length: number of bytes in array
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 *          wait: boolean indicating to wait for write or not
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 * Output   0 .. success
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 *          1 .. length to long for buffer
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 *          2 .. address send, NACK received
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 *          3 .. data send, NACK received
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 *          4 .. other twi error (lost bus arbitration, bus error, ..)
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 */
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uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait)
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{
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  uint8_t i;
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  // ensure data will fit into buffer
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  if(TWI_BUFFER_LENGTH < length){
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    return 1;
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  }
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  // wait until twi is ready, become master transmitter
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  while(TWI_READY != twi_state){
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    continue;
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  }
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  twi_state = TWI_MTX;
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  // reset error state (0xFF.. no error occured)
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  twi_error = 0xFF;
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  // initialize buffer iteration vars
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  twi_masterBufferIndex = 0;
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  twi_masterBufferLength = length;
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  // copy data to twi buffer
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  for(i = 0; i < length; ++i){
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    twi_masterBuffer[i] = data[i];
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  }
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  // build sla+w, slave device address + w bit
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  twi_slarw = TW_WRITE;
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  twi_slarw |= address << 1;
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  // send start condition
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  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
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  // wait for write operation to complete
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  while(wait && (TWI_MTX == twi_state)){
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    continue;
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  }
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  if (twi_error == 0xFF)
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    return 0;        // success
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  else if (twi_error == TW_MT_SLA_NACK)
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    return 2;        // error: address send, nack received
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  else if (twi_error == TW_MT_DATA_NACK)
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    return 3;        // error: data send, nack received
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  else
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    return 4;        // other twi error
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}
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/* 
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 * Function twi_transmit
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 * Desc     fills slave tx buffer with data
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 *          must be called in slave tx event callback
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 * Input    data: pointer to byte array
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 *          length: number of bytes in array
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 * Output   1 length too long for buffer
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 *          2 not slave transmitter
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 *          0 ok
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 */
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uint8_t twi_transmit(const uint8_t* data, uint8_t length)
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{
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  uint8_t i;
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  // ensure data will fit into buffer
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  if(TWI_BUFFER_LENGTH < length){
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    return 1;
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  }
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  // ensure we are currently a slave transmitter
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  if(TWI_STX != twi_state){
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    return 2;
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  }
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  // set length and copy data into tx buffer
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  twi_txBufferLength = length;
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  for(i = 0; i < length; ++i){
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    twi_txBuffer[i] = data[i];
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  }
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  return 0;
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}
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/* 
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 * Function twi_attachSlaveRxEvent
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 * Desc     sets function called before a slave read operation
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 * Input    function: callback function to use
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 * Output   none
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 */
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void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) )
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{
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  twi_onSlaveReceive = function;
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}
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/* 
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 * Function twi_attachSlaveTxEvent
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 * Desc     sets function called before a slave write operation
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 * Input    function: callback function to use
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 * Output   none
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 */
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void twi_attachSlaveTxEvent( void (*function)(void) )
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{
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  twi_onSlaveTransmit = function;
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}
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/* 
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 * Function twi_reply
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 * Desc     sends byte or readys receive line
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 * Input    ack: byte indicating to ack or to nack
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 * Output   none
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 */
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void twi_reply(uint8_t ack)
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{
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  // transmit master read ready signal, with or without ack
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  if(ack){
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    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA);
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  }else{
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          TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT);
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  }
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}
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/* 
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 * Function twi_stop
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 * Desc     relinquishes bus master status
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 * Input    none
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 * Output   none
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 */
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void twi_stop(void)
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{
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  // send stop condition
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  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO);
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  // wait for stop condition to be exectued on bus
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  // TWINT is not set after a stop condition!
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  while(TWCR & _BV(TWSTO)){
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    continue;
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  }
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  // update twi state
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  twi_state = TWI_READY;
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}
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/* 
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 * Function twi_releaseBus
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 * Desc     releases bus control
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 * Input    none
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 * Output   none
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 */
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void twi_releaseBus(void)
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{
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  // release bus
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  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT);
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  // update twi state
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  twi_state = TWI_READY;
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}
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SIGNAL(TWI_vect)
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{
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  switch(TW_STATUS){
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    // All Master
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    case TW_START:     // sent start condition
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    case TW_REP_START: // sent repeated start condition
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      // copy device address and r/w bit to output register and ack
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      TWDR = twi_slarw;
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      twi_reply(1);
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      break;
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    // Master Transmitter
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    case TW_MT_SLA_ACK:  // slave receiver acked address
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    case TW_MT_DATA_ACK: // slave receiver acked data
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      // if there is data to send, send it, otherwise stop 
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      if(twi_masterBufferIndex < twi_masterBufferLength){
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        // copy data to output register and ack
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        TWDR = twi_masterBuffer[twi_masterBufferIndex++];
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        twi_reply(1);
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      }else{
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        twi_stop();
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      }
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      break;
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    case TW_MT_SLA_NACK:  // address sent, nack received
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      twi_error = TW_MT_SLA_NACK;
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      twi_stop();
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      break;
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    case TW_MT_DATA_NACK: // data sent, nack received
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      twi_error = TW_MT_DATA_NACK;
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      twi_stop();
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      break;
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    case TW_MT_ARB_LOST: // lost bus arbitration
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      twi_error = TW_MT_ARB_LOST;
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      twi_releaseBus();
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      break;
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    // Master Receiver
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    case TW_MR_DATA_ACK: // data received, ack sent
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      // put byte into buffer
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      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
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    case TW_MR_SLA_ACK:  // address sent, ack received
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      // ack if more bytes are expected, otherwise nack
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      if(twi_masterBufferIndex < twi_masterBufferLength){
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        twi_reply(1);
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      }else{
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        twi_reply(0);
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      }
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      break;
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    case TW_MR_DATA_NACK: // data received, nack sent
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      // put final byte into buffer
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      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
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    case TW_MR_SLA_NACK: // address sent, nack received
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      twi_stop();
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      break;
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    // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case
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    // Slave Receiver
381
    case TW_SR_SLA_ACK:   // addressed, returned ack
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    case TW_SR_GCALL_ACK: // addressed generally, returned ack
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    case TW_SR_ARB_LOST_SLA_ACK:   // lost arbitration, returned ack
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    case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack
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      // enter slave receiver mode
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      twi_state = TWI_SRX;
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      // indicate that rx buffer can be overwritten and ack
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      twi_rxBufferIndex = 0;
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      twi_reply(1);
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      break;
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    case TW_SR_DATA_ACK:       // data received, returned ack
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    case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack
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      // if there is still room in the rx buffer
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      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
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        // put byte in buffer and ack
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        twi_rxBuffer[twi_rxBufferIndex++] = TWDR;
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        twi_reply(1);
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      }else{
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        // otherwise nack
400
        twi_reply(0);
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      }
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      break;
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    case TW_SR_STOP: // stop or repeated start condition received
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      // put a null char after data if there's room
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      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
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        twi_rxBuffer[twi_rxBufferIndex] = '\0';
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      }
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      // sends ack and stops interface for clock stretching
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      twi_stop();
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      // callback to user defined callback
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      twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex);
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      // since we submit rx buffer to "wire" library, we can reset it
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      twi_rxBufferIndex = 0;
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      // ack future responses and leave slave receiver state
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      twi_releaseBus();
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      break;
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    case TW_SR_DATA_NACK:       // data received, returned nack
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    case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack
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      // nack back at master
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      twi_reply(0);
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      break;
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    // Slave Transmitter
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    case TW_ST_SLA_ACK:          // addressed, returned ack
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    case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack
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      // enter slave transmitter mode
427
      twi_state = TWI_STX;
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      // ready the tx buffer index for iteration
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      twi_txBufferIndex = 0;
430
      // set tx buffer length to be zero, to verify if user changes it
431
      twi_txBufferLength = 0;
432
      // request for txBuffer to be filled and length to be set
433
      // note: user must call twi_transmit(bytes, length) to do this
434
      twi_onSlaveTransmit();
435
      // if they didn't change buffer & length, initialize it
436
      if(0 == twi_txBufferLength){
437
        twi_txBufferLength = 1;
438
        twi_txBuffer[0] = 0x00;
439
      }
440
      // transmit first byte from buffer, fall
441
    case TW_ST_DATA_ACK: // byte sent, ack returned
442
      // copy data to output register
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      TWDR = twi_txBuffer[twi_txBufferIndex++];
444
      // if there is more to send, ack, otherwise nack
445
      if(twi_txBufferIndex < twi_txBufferLength){
446
        twi_reply(1);
447
      }else{
448
        twi_reply(0);
449
      }
450
      break;
451
    case TW_ST_DATA_NACK: // received nack, we are done 
452
    case TW_ST_LAST_DATA: // received ack, but we are done already!
453
      // ack future responses
454
      twi_reply(1);
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      // leave slave receiver state
456
      twi_state = TWI_READY;
457
      break;
458

    
459
    // All
460
    case TW_NO_INFO:   // no state information
461
      break;
462
    case TW_BUS_ERROR: // bus error, illegal stop/start
463
      twi_error = TW_BUS_ERROR;
464
      twi_stop();
465
      break;
466
  }
467
}
468