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1 | 58d82c77 | Tom Mullins | /*
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2 | twi.c - TWI/I2C library for Wiring & Arduino
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3 | Copyright (c) 2006 Nicholas Zambetti. All right reserved.
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4 | |||
5 | This library is free software; you can redistribute it and/or
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6 | modify it under the terms of the GNU Lesser General Public
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7 | License as published by the Free Software Foundation; either
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8 | version 2.1 of the License, or (at your option) any later version.
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9 | |||
10 | This library is distributed in the hope that it will be useful,
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11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 | Lesser General Public License for more details.
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14 | |||
15 | You should have received a copy of the GNU Lesser General Public
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16 | License along with this library; if not, write to the Free Software
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17 | Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18 | */
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19 | |||
20 | #include <math.h> |
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21 | #include <stdlib.h> |
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22 | #include <inttypes.h> |
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23 | #include <avr/io.h> |
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24 | #include <avr/interrupt.h> |
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25 | #include <compat/twi.h> |
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26 | #include "Arduino.h" // for digitalWrite |
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27 | |||
28 | #ifndef cbi
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29 | #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
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30 | #endif
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31 | |||
32 | #ifndef sbi
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33 | #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
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34 | #endif
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35 | |||
36 | #include "pins_arduino.h" |
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37 | #include "twi.h" |
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38 | |||
39 | static volatile uint8_t twi_state; |
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40 | static uint8_t twi_slarw;
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41 | |||
42 | static void (*twi_onSlaveTransmit)(void); |
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43 | static void (*twi_onSlaveReceive)(uint8_t*, int); |
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44 | |||
45 | static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH];
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46 | static volatile uint8_t twi_masterBufferIndex; |
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47 | static uint8_t twi_masterBufferLength;
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48 | |||
49 | static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH];
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50 | static volatile uint8_t twi_txBufferIndex; |
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51 | static volatile uint8_t twi_txBufferLength; |
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52 | |||
53 | static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH];
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54 | static volatile uint8_t twi_rxBufferIndex; |
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55 | |||
56 | static volatile uint8_t twi_error; |
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57 | |||
58 | /*
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59 | * Function twi_init
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60 | * Desc readys twi pins and sets twi bitrate
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61 | * Input none
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62 | * Output none
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63 | */
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64 | void twi_init(void) |
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65 | { |
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66 | // initialize state
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67 | twi_state = TWI_READY; |
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68 | |||
69 | // activate internal pullups for twi.
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70 | digitalWrite(SDA, 1);
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71 | digitalWrite(SCL, 1);
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72 | |||
73 | // initialize twi prescaler and bit rate
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74 | cbi(TWSR, TWPS0); |
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75 | cbi(TWSR, TWPS1); |
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76 | TWBR = ((F_CPU / TWI_FREQ) - 16) / 2; |
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77 | |||
78 | /* twi bit rate formula from atmega128 manual pg 204
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79 | SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
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80 | note: TWBR should be 10 or higher for master mode
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81 | It is 72 for a 16mhz Wiring board with 100kHz TWI */
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82 | |||
83 | // enable twi module, acks, and twi interrupt
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84 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA); |
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85 | } |
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86 | |||
87 | /*
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88 | * Function twi_slaveInit
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89 | * Desc sets slave address and enables interrupt
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90 | * Input none
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91 | * Output none
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92 | */
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93 | void twi_setAddress(uint8_t address)
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94 | { |
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95 | // set twi slave address (skip over TWGCE bit)
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96 | TWAR = address << 1;
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97 | } |
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98 | |||
99 | /*
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100 | * Function twi_readFrom
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101 | * Desc attempts to become twi bus master and read a
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102 | * series of bytes from a device on the bus
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103 | * Input address: 7bit i2c device address
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104 | * data: pointer to byte array
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105 | * length: number of bytes to read into array
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106 | * Output number of bytes read
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107 | */
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108 | uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length) |
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109 | { |
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110 | uint8_t i; |
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111 | |||
112 | // ensure data will fit into buffer
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113 | if(TWI_BUFFER_LENGTH < length){
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114 | return 0; |
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115 | } |
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116 | |||
117 | // wait until twi is ready, become master receiver
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118 | while(TWI_READY != twi_state){
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119 | continue;
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120 | } |
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121 | twi_state = TWI_MRX; |
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122 | // reset error state (0xFF.. no error occured)
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123 | twi_error = 0xFF;
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124 | |||
125 | // initialize buffer iteration vars
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126 | twi_masterBufferIndex = 0;
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127 | twi_masterBufferLength = length-1; // This is not intuitive, read on... |
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128 | // On receive, the previously configured ACK/NACK setting is transmitted in
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129 | // response to the received byte before the interrupt is signalled.
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130 | // Therefor we must actually set NACK when the _next_ to last byte is
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131 | // received, causing that NACK to be sent in response to receiving the last
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132 | // expected byte of data.
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133 | |||
134 | // build sla+w, slave device address + w bit
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135 | twi_slarw = TW_READ; |
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136 | twi_slarw |= address << 1;
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137 | |||
138 | // send start condition
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139 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA); |
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140 | |||
141 | // wait for read operation to complete
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142 | while(TWI_MRX == twi_state){
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143 | continue;
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144 | } |
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145 | |||
146 | if (twi_masterBufferIndex < length)
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147 | length = twi_masterBufferIndex; |
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148 | |||
149 | // copy twi buffer to data
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150 | for(i = 0; i < length; ++i){ |
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151 | data[i] = twi_masterBuffer[i]; |
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152 | } |
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153 | |||
154 | return length;
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155 | } |
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156 | |||
157 | /*
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158 | * Function twi_writeTo
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159 | * Desc attempts to become twi bus master and write a
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160 | * series of bytes to a device on the bus
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161 | * Input address: 7bit i2c device address
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162 | * data: pointer to byte array
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163 | * length: number of bytes in array
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164 | * wait: boolean indicating to wait for write or not
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165 | * Output 0 .. success
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166 | * 1 .. length to long for buffer
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167 | * 2 .. address send, NACK received
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168 | * 3 .. data send, NACK received
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169 | * 4 .. other twi error (lost bus arbitration, bus error, ..)
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170 | */
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171 | uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait) |
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172 | { |
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173 | uint8_t i; |
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174 | |||
175 | // ensure data will fit into buffer
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176 | if(TWI_BUFFER_LENGTH < length){
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177 | return 1; |
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178 | } |
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179 | |||
180 | // wait until twi is ready, become master transmitter
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181 | while(TWI_READY != twi_state){
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182 | continue;
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183 | } |
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184 | twi_state = TWI_MTX; |
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185 | // reset error state (0xFF.. no error occured)
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186 | twi_error = 0xFF;
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187 | |||
188 | // initialize buffer iteration vars
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189 | twi_masterBufferIndex = 0;
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190 | twi_masterBufferLength = length; |
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191 | |||
192 | // copy data to twi buffer
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193 | for(i = 0; i < length; ++i){ |
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194 | twi_masterBuffer[i] = data[i]; |
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195 | } |
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196 | |||
197 | // build sla+w, slave device address + w bit
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198 | twi_slarw = TW_WRITE; |
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199 | twi_slarw |= address << 1;
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200 | |||
201 | // send start condition
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202 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA); |
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203 | |||
204 | // wait for write operation to complete
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205 | while(wait && (TWI_MTX == twi_state)){
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206 | continue;
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207 | } |
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208 | |||
209 | if (twi_error == 0xFF) |
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210 | return 0; // success |
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211 | else if (twi_error == TW_MT_SLA_NACK) |
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212 | return 2; // error: address send, nack received |
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213 | else if (twi_error == TW_MT_DATA_NACK) |
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214 | return 3; // error: data send, nack received |
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215 | else
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216 | return 4; // other twi error |
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217 | } |
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218 | |||
219 | /*
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220 | * Function twi_transmit
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221 | * Desc fills slave tx buffer with data
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222 | * must be called in slave tx event callback
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223 | * Input data: pointer to byte array
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224 | * length: number of bytes in array
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225 | * Output 1 length too long for buffer
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226 | * 2 not slave transmitter
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227 | * 0 ok
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228 | */
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229 | uint8_t twi_transmit(const uint8_t* data, uint8_t length)
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230 | { |
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231 | uint8_t i; |
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232 | |||
233 | // ensure data will fit into buffer
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234 | if(TWI_BUFFER_LENGTH < length){
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235 | return 1; |
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236 | } |
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237 | |||
238 | // ensure we are currently a slave transmitter
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239 | if(TWI_STX != twi_state){
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240 | return 2; |
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241 | } |
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242 | |||
243 | // set length and copy data into tx buffer
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244 | twi_txBufferLength = length; |
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245 | for(i = 0; i < length; ++i){ |
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246 | twi_txBuffer[i] = data[i]; |
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247 | } |
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248 | |||
249 | return 0; |
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250 | } |
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251 | |||
252 | /*
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253 | * Function twi_attachSlaveRxEvent
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254 | * Desc sets function called before a slave read operation
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255 | * Input function: callback function to use
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256 | * Output none
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257 | */
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258 | void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) ) |
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259 | { |
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260 | twi_onSlaveReceive = function; |
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261 | } |
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262 | |||
263 | /*
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264 | * Function twi_attachSlaveTxEvent
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265 | * Desc sets function called before a slave write operation
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266 | * Input function: callback function to use
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267 | * Output none
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268 | */
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269 | void twi_attachSlaveTxEvent( void (*function)(void) ) |
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270 | { |
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271 | twi_onSlaveTransmit = function; |
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272 | } |
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273 | |||
274 | /*
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275 | * Function twi_reply
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276 | * Desc sends byte or readys receive line
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277 | * Input ack: byte indicating to ack or to nack
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278 | * Output none
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279 | */
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280 | void twi_reply(uint8_t ack)
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281 | { |
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282 | // transmit master read ready signal, with or without ack
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283 | if(ack){
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284 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA); |
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285 | }else{
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286 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT); |
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287 | } |
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288 | } |
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289 | |||
290 | /*
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291 | * Function twi_stop
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292 | * Desc relinquishes bus master status
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293 | * Input none
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294 | * Output none
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295 | */
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296 | void twi_stop(void) |
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297 | { |
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298 | // send stop condition
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299 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO); |
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300 | |||
301 | // wait for stop condition to be exectued on bus
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302 | // TWINT is not set after a stop condition!
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303 | while(TWCR & _BV(TWSTO)){
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304 | continue;
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305 | } |
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306 | |||
307 | // update twi state
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308 | twi_state = TWI_READY; |
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309 | } |
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310 | |||
311 | /*
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312 | * Function twi_releaseBus
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313 | * Desc releases bus control
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314 | * Input none
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315 | * Output none
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316 | */
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317 | void twi_releaseBus(void) |
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318 | { |
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319 | // release bus
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320 | TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT); |
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321 | |||
322 | // update twi state
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323 | twi_state = TWI_READY; |
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324 | } |
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325 | |||
326 | SIGNAL(TWI_vect) |
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327 | { |
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328 | switch(TW_STATUS){
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329 | // All Master
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330 | case TW_START: // sent start condition |
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331 | case TW_REP_START: // sent repeated start condition |
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332 | // copy device address and r/w bit to output register and ack
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333 | TWDR = twi_slarw; |
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334 | twi_reply(1);
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335 | break;
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336 | |||
337 | // Master Transmitter
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338 | case TW_MT_SLA_ACK: // slave receiver acked address |
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339 | case TW_MT_DATA_ACK: // slave receiver acked data |
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340 | // if there is data to send, send it, otherwise stop
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341 | if(twi_masterBufferIndex < twi_masterBufferLength){
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342 | // copy data to output register and ack
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343 | TWDR = twi_masterBuffer[twi_masterBufferIndex++]; |
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344 | twi_reply(1);
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345 | }else{
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346 | twi_stop(); |
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347 | } |
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348 | break;
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349 | case TW_MT_SLA_NACK: // address sent, nack received |
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350 | twi_error = TW_MT_SLA_NACK; |
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351 | twi_stop(); |
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352 | break;
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353 | case TW_MT_DATA_NACK: // data sent, nack received |
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354 | twi_error = TW_MT_DATA_NACK; |
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355 | twi_stop(); |
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356 | break;
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357 | case TW_MT_ARB_LOST: // lost bus arbitration |
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358 | twi_error = TW_MT_ARB_LOST; |
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359 | twi_releaseBus(); |
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360 | break;
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361 | |||
362 | // Master Receiver
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363 | case TW_MR_DATA_ACK: // data received, ack sent |
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364 | // put byte into buffer
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365 | twi_masterBuffer[twi_masterBufferIndex++] = TWDR; |
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366 | case TW_MR_SLA_ACK: // address sent, ack received |
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367 | // ack if more bytes are expected, otherwise nack
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368 | if(twi_masterBufferIndex < twi_masterBufferLength){
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369 | twi_reply(1);
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370 | }else{
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371 | twi_reply(0);
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372 | } |
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373 | break;
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374 | case TW_MR_DATA_NACK: // data received, nack sent |
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375 | // put final byte into buffer
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376 | twi_masterBuffer[twi_masterBufferIndex++] = TWDR; |
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377 | case TW_MR_SLA_NACK: // address sent, nack received |
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378 | twi_stop(); |
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379 | break;
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380 | // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case
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381 | |||
382 | // Slave Receiver
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383 | case TW_SR_SLA_ACK: // addressed, returned ack |
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384 | case TW_SR_GCALL_ACK: // addressed generally, returned ack |
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385 | case TW_SR_ARB_LOST_SLA_ACK: // lost arbitration, returned ack |
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386 | case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack |
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387 | // enter slave receiver mode
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388 | twi_state = TWI_SRX; |
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389 | // indicate that rx buffer can be overwritten and ack
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390 | twi_rxBufferIndex = 0;
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391 | twi_reply(1);
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392 | break;
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393 | case TW_SR_DATA_ACK: // data received, returned ack |
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394 | case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack |
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395 | // if there is still room in the rx buffer
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396 | if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
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397 | // put byte in buffer and ack
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398 | twi_rxBuffer[twi_rxBufferIndex++] = TWDR; |
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399 | twi_reply(1);
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400 | }else{
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401 | // otherwise nack
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402 | twi_reply(0);
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403 | } |
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404 | break;
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405 | case TW_SR_STOP: // stop or repeated start condition received |
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406 | // put a null char after data if there's room
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407 | if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
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408 | twi_rxBuffer[twi_rxBufferIndex] = '\0';
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409 | } |
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410 | // sends ack and stops interface for clock stretching
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411 | twi_stop(); |
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412 | // callback to user defined callback
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413 | twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex); |
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414 | // since we submit rx buffer to "wire" library, we can reset it
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415 | twi_rxBufferIndex = 0;
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416 | // ack future responses and leave slave receiver state
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417 | twi_releaseBus(); |
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418 | break;
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419 | case TW_SR_DATA_NACK: // data received, returned nack |
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420 | case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack |
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421 | // nack back at master
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422 | twi_reply(0);
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423 | break;
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424 | |||
425 | // Slave Transmitter
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426 | case TW_ST_SLA_ACK: // addressed, returned ack |
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427 | case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack |
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428 | // enter slave transmitter mode
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429 | twi_state = TWI_STX; |
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430 | // ready the tx buffer index for iteration
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431 | twi_txBufferIndex = 0;
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432 | // set tx buffer length to be zero, to verify if user changes it
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433 | twi_txBufferLength = 0;
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434 | // request for txBuffer to be filled and length to be set
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435 | // note: user must call twi_transmit(bytes, length) to do this
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436 | twi_onSlaveTransmit(); |
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437 | // if they didn't change buffer & length, initialize it
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438 | if(0 == twi_txBufferLength){ |
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439 | twi_txBufferLength = 1;
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440 | twi_txBuffer[0] = 0x00; |
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441 | } |
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442 | // transmit first byte from buffer, fall
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443 | case TW_ST_DATA_ACK: // byte sent, ack returned |
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444 | // copy data to output register
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445 | TWDR = twi_txBuffer[twi_txBufferIndex++]; |
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446 | // if there is more to send, ack, otherwise nack
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447 | if(twi_txBufferIndex < twi_txBufferLength){
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448 | twi_reply(1);
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449 | }else{
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450 | twi_reply(0);
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451 | } |
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452 | break;
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453 | case TW_ST_DATA_NACK: // received nack, we are done |
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454 | case TW_ST_LAST_DATA: // received ack, but we are done already! |
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455 | // ack future responses
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456 | twi_reply(1);
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457 | // leave slave receiver state
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458 | twi_state = TWI_READY; |
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459 | break;
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460 | |||
461 | // All
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462 | case TW_NO_INFO: // no state information |
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463 | break;
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464 | case TW_BUS_ERROR: // bus error, illegal stop/start |
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465 | twi_error = TW_BUS_ERROR; |
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466 | twi_stop(); |
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467 | break;
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468 | } |
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469 | } |