477 lines
13 KiB
C
477 lines
13 KiB
C
/*
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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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#if defined(__AVR_ATmega168__) || defined(__AVR_ATmega8__) || defined(__AVR_ATmega328P__)
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// activate internal pull-ups for twi
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// as per note from atmega8 manual pg167
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sbi(PORTC, 4);
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sbi(PORTC, 5);
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#else
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// activate internal pull-ups for twi
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// as per note from atmega128 manual pg204
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sbi(PORTD, 0);
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sbi(PORTD, 1);
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#endif
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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 = ((CPU_FREQ / 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(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
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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
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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
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twi_state = TWI_STX;
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// ready the tx buffer index for iteration
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twi_txBufferIndex = 0;
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// set tx buffer length to be zero, to verify if user changes it
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twi_txBufferLength = 0;
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// request for txBuffer to be filled and length to be set
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// note: user must call twi_transmit(bytes, length) to do this
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twi_onSlaveTransmit();
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// if they didn't change buffer & length, initialize it
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if(0 == twi_txBufferLength){
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twi_txBufferLength = 1;
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twi_txBuffer[0] = 0x00;
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}
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// transmit first byte from buffer, fall
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case TW_ST_DATA_ACK: // byte sent, ack returned
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// copy data to output register
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TWDR = twi_txBuffer[twi_txBufferIndex++];
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// if there is more to send, ack, otherwise nack
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if(twi_txBufferIndex < twi_txBufferLength){
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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_ST_DATA_NACK: // received nack, we are done
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case TW_ST_LAST_DATA: // received ack, but we are done already!
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// ack future responses
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twi_reply(1);
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// leave slave receiver state
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twi_state = TWI_READY;
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break;
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// All
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case TW_NO_INFO: // no state information
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break;
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case TW_BUS_ERROR: // bus error, illegal stop/start
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twi_error = TW_BUS_ERROR;
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twi_stop();
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break;
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}
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}
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