source: arduino-1-6-7/trunk/fuentes/arduino-ide-amd64/hardware/arduino/avr/libraries/Wire/src/utility/twi.c @ 4837

Last change on this file since 4837 was 4837, checked in by daduve, 2 years ago

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1/*
2  twi.c - TWI/I2C library for Wiring & Arduino
3  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
4
5  This library is free software; you can redistribute it and/or
6  modify it under the terms of the GNU Lesser General Public
7  License as published by the Free Software Foundation; either
8  version 2.1 of the License, or (at your option) any later version.
9
10  This library is distributed in the hope that it will be useful,
11  but WITHOUT ANY WARRANTY; without even the implied warranty of
12  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13  Lesser General Public License for more details.
14
15  You should have received a copy of the GNU Lesser General Public
16  License along with this library; if not, write to the Free Software
17  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
18
19  Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
20*/
21
22#include <math.h>
23#include <stdlib.h>
24#include <inttypes.h>
25#include <avr/io.h>
26#include <avr/interrupt.h>
27#include <compat/twi.h>
28#include "Arduino.h" // for digitalWrite
29
30#ifndef cbi
31#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
32#endif
33
34#ifndef sbi
35#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
36#endif
37
38#include "pins_arduino.h"
39#include "twi.h"
40
41static volatile uint8_t twi_state;
42static volatile uint8_t twi_slarw;
43static volatile uint8_t twi_sendStop;                   // should the transaction end with a stop
44static volatile uint8_t twi_inRepStart;                 // in the middle of a repeated start
45
46static void (*twi_onSlaveTransmit)(void);
47static void (*twi_onSlaveReceive)(uint8_t*, int);
48
49static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH];
50static volatile uint8_t twi_masterBufferIndex;
51static volatile uint8_t twi_masterBufferLength;
52
53static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH];
54static volatile uint8_t twi_txBufferIndex;
55static volatile uint8_t twi_txBufferLength;
56
57static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH];
58static volatile uint8_t twi_rxBufferIndex;
59
60static volatile uint8_t twi_error;
61
62/*
63 * Function twi_init
64 * Desc     readys twi pins and sets twi bitrate
65 * Input    none
66 * Output   none
67 */
68void twi_init(void)
69{
70  // initialize state
71  twi_state = TWI_READY;
72  twi_sendStop = true;          // default value
73  twi_inRepStart = false;
74 
75  // activate internal pullups for twi.
76  digitalWrite(SDA, 1);
77  digitalWrite(SCL, 1);
78
79  // initialize twi prescaler and bit rate
80  cbi(TWSR, TWPS0);
81  cbi(TWSR, TWPS1);
82  TWBR = ((F_CPU / TWI_FREQ) - 16) / 2;
83
84  /* twi bit rate formula from atmega128 manual pg 204
85  SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
86  note: TWBR should be 10 or higher for master mode
87  It is 72 for a 16mhz Wiring board with 100kHz TWI */
88
89  // enable twi module, acks, and twi interrupt
90  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA);
91}
92
93/*
94 * Function twi_disable
95 * Desc     disables twi pins
96 * Input    none
97 * Output   none
98 */
99void twi_disable(void)
100{
101  // disable twi module, acks, and twi interrupt
102  TWCR &= ~(_BV(TWEN) | _BV(TWIE) | _BV(TWEA));
103
104  // deactivate internal pullups for twi.
105  digitalWrite(SDA, 0);
106  digitalWrite(SCL, 0);
107}
108
109/*
110 * Function twi_slaveInit
111 * Desc     sets slave address and enables interrupt
112 * Input    none
113 * Output   none
114 */
115void twi_setAddress(uint8_t address)
116{
117  // set twi slave address (skip over TWGCE bit)
118  TWAR = address << 1;
119}
120
121/*
122 * Function twi_setClock
123 * Desc     sets twi bit rate
124 * Input    Clock Frequency
125 * Output   none
126 */
127void twi_setFrequency(uint32_t frequency)
128{
129  TWBR = ((F_CPU / frequency) - 16) / 2;
130 
131  /* twi bit rate formula from atmega128 manual pg 204
132  SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
133  note: TWBR should be 10 or higher for master mode
134  It is 72 for a 16mhz Wiring board with 100kHz TWI */
135}
136
137/*
138 * Function twi_readFrom
139 * Desc     attempts to become twi bus master and read a
140 *          series of bytes from a device on the bus
141 * Input    address: 7bit i2c device address
142 *          data: pointer to byte array
143 *          length: number of bytes to read into array
144 *          sendStop: Boolean indicating whether to send a stop at the end
145 * Output   number of bytes read
146 */
147uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sendStop)
148{
149  uint8_t i;
150
151  // ensure data will fit into buffer
152  if(TWI_BUFFER_LENGTH < length){
153    return 0;
154  }
155
156  // wait until twi is ready, become master receiver
157  while(TWI_READY != twi_state){
158    continue;
159  }
160  twi_state = TWI_MRX;
161  twi_sendStop = sendStop;
162  // reset error state (0xFF.. no error occured)
163  twi_error = 0xFF;
164
165  // initialize buffer iteration vars
166  twi_masterBufferIndex = 0;
167  twi_masterBufferLength = length-1;  // This is not intuitive, read on...
168  // On receive, the previously configured ACK/NACK setting is transmitted in
169  // response to the received byte before the interrupt is signalled.
170  // Therefor we must actually set NACK when the _next_ to last byte is
171  // received, causing that NACK to be sent in response to receiving the last
172  // expected byte of data.
173
174  // build sla+w, slave device address + w bit
175  twi_slarw = TW_READ;
176  twi_slarw |= address << 1;
177
178  if (true == twi_inRepStart) {
179    // if we're in the repeated start state, then we've already sent the start,
180    // (@@@ we hope), and the TWI statemachine is just waiting for the address byte.
181    // We need to remove ourselves from the repeated start state before we enable interrupts,
182    // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning
183    // up. Also, don't enable the START interrupt. There may be one pending from the
184    // repeated start that we sent ourselves, and that would really confuse things.
185    twi_inRepStart = false;                     // remember, we're dealing with an ASYNC ISR
186    do {
187      TWDR = twi_slarw;
188    } while(TWCR & _BV(TWWC));
189    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);      // enable INTs, but not START
190  }
191  else
192    // send start condition
193    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);
194
195  // wait for read operation to complete
196  while(TWI_MRX == twi_state){
197    continue;
198  }
199
200  if (twi_masterBufferIndex < length)
201    length = twi_masterBufferIndex;
202
203  // copy twi buffer to data
204  for(i = 0; i < length; ++i){
205    data[i] = twi_masterBuffer[i];
206  }
207       
208  return length;
209}
210
211/*
212 * Function twi_writeTo
213 * Desc     attempts to become twi bus master and write a
214 *          series of bytes to a device on the bus
215 * Input    address: 7bit i2c device address
216 *          data: pointer to byte array
217 *          length: number of bytes in array
218 *          wait: boolean indicating to wait for write or not
219 *          sendStop: boolean indicating whether or not to send a stop at the end
220 * Output   0 .. success
221 *          1 .. length to long for buffer
222 *          2 .. address send, NACK received
223 *          3 .. data send, NACK received
224 *          4 .. other twi error (lost bus arbitration, bus error, ..)
225 */
226uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait, uint8_t sendStop)
227{
228  uint8_t i;
229
230  // ensure data will fit into buffer
231  if(TWI_BUFFER_LENGTH < length){
232    return 1;
233  }
234
235  // wait until twi is ready, become master transmitter
236  while(TWI_READY != twi_state){
237    continue;
238  }
239  twi_state = TWI_MTX;
240  twi_sendStop = sendStop;
241  // reset error state (0xFF.. no error occured)
242  twi_error = 0xFF;
243
244  // initialize buffer iteration vars
245  twi_masterBufferIndex = 0;
246  twi_masterBufferLength = length;
247 
248  // copy data to twi buffer
249  for(i = 0; i < length; ++i){
250    twi_masterBuffer[i] = data[i];
251  }
252 
253  // build sla+w, slave device address + w bit
254  twi_slarw = TW_WRITE;
255  twi_slarw |= address << 1;
256 
257  // if we're in a repeated start, then we've already sent the START
258  // in the ISR. Don't do it again.
259  //
260  if (true == twi_inRepStart) {
261    // if we're in the repeated start state, then we've already sent the start,
262    // (@@@ we hope), and the TWI statemachine is just waiting for the address byte.
263    // We need to remove ourselves from the repeated start state before we enable interrupts,
264    // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning
265    // up. Also, don't enable the START interrupt. There may be one pending from the
266    // repeated start that we sent outselves, and that would really confuse things.
267    twi_inRepStart = false;                     // remember, we're dealing with an ASYNC ISR
268    do {
269      TWDR = twi_slarw;                         
270    } while(TWCR & _BV(TWWC));
271    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);      // enable INTs, but not START
272  }
273  else
274    // send start condition
275    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE) | _BV(TWSTA); // enable INTs
276
277  // wait for write operation to complete
278  while(wait && (TWI_MTX == twi_state)){
279    continue;
280  }
281 
282  if (twi_error == 0xFF)
283    return 0;   // success
284  else if (twi_error == TW_MT_SLA_NACK)
285    return 2;   // error: address send, nack received
286  else if (twi_error == TW_MT_DATA_NACK)
287    return 3;   // error: data send, nack received
288  else
289    return 4;   // other twi error
290}
291
292/*
293 * Function twi_transmit
294 * Desc     fills slave tx buffer with data
295 *          must be called in slave tx event callback
296 * Input    data: pointer to byte array
297 *          length: number of bytes in array
298 * Output   1 length too long for buffer
299 *          2 not slave transmitter
300 *          0 ok
301 */
302uint8_t twi_transmit(const uint8_t* data, uint8_t length)
303{
304  uint8_t i;
305
306  // ensure data will fit into buffer
307  if(TWI_BUFFER_LENGTH < (twi_txBufferLength+length)){
308    return 1;
309  }
310 
311  // ensure we are currently a slave transmitter
312  if(TWI_STX != twi_state){
313    return 2;
314  }
315 
316  // set length and copy data into tx buffer
317  for(i = 0; i < length; ++i){
318    twi_txBuffer[twi_txBufferLength+i] = data[i];
319  }
320  twi_txBufferLength += length;
321 
322  return 0;
323}
324
325/*
326 * Function twi_attachSlaveRxEvent
327 * Desc     sets function called before a slave read operation
328 * Input    function: callback function to use
329 * Output   none
330 */
331void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) )
332{
333  twi_onSlaveReceive = function;
334}
335
336/*
337 * Function twi_attachSlaveTxEvent
338 * Desc     sets function called before a slave write operation
339 * Input    function: callback function to use
340 * Output   none
341 */
342void twi_attachSlaveTxEvent( void (*function)(void) )
343{
344  twi_onSlaveTransmit = function;
345}
346
347/*
348 * Function twi_reply
349 * Desc     sends byte or readys receive line
350 * Input    ack: byte indicating to ack or to nack
351 * Output   none
352 */
353void twi_reply(uint8_t ack)
354{
355  // transmit master read ready signal, with or without ack
356  if(ack){
357    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA);
358  }else{
359          TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT);
360  }
361}
362
363/*
364 * Function twi_stop
365 * Desc     relinquishes bus master status
366 * Input    none
367 * Output   none
368 */
369void twi_stop(void)
370{
371  // send stop condition
372  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO);
373
374  // wait for stop condition to be exectued on bus
375  // TWINT is not set after a stop condition!
376  while(TWCR & _BV(TWSTO)){
377    continue;
378  }
379
380  // update twi state
381  twi_state = TWI_READY;
382}
383
384/*
385 * Function twi_releaseBus
386 * Desc     releases bus control
387 * Input    none
388 * Output   none
389 */
390void twi_releaseBus(void)
391{
392  // release bus
393  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT);
394
395  // update twi state
396  twi_state = TWI_READY;
397}
398
399ISR(TWI_vect)
400{
401  switch(TW_STATUS){
402    // All Master
403    case TW_START:     // sent start condition
404    case TW_REP_START: // sent repeated start condition
405      // copy device address and r/w bit to output register and ack
406      TWDR = twi_slarw;
407      twi_reply(1);
408      break;
409
410    // Master Transmitter
411    case TW_MT_SLA_ACK:  // slave receiver acked address
412    case TW_MT_DATA_ACK: // slave receiver acked data
413      // if there is data to send, send it, otherwise stop
414      if(twi_masterBufferIndex < twi_masterBufferLength){
415        // copy data to output register and ack
416        TWDR = twi_masterBuffer[twi_masterBufferIndex++];
417        twi_reply(1);
418      }else{
419        if (twi_sendStop)
420          twi_stop();
421        else {
422          twi_inRepStart = true;        // we're gonna send the START
423          // don't enable the interrupt. We'll generate the start, but we
424          // avoid handling the interrupt until we're in the next transaction,
425          // at the point where we would normally issue the start.
426          TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ;
427          twi_state = TWI_READY;
428        }
429      }
430      break;
431    case TW_MT_SLA_NACK:  // address sent, nack received
432      twi_error = TW_MT_SLA_NACK;
433      twi_stop();
434      break;
435    case TW_MT_DATA_NACK: // data sent, nack received
436      twi_error = TW_MT_DATA_NACK;
437      twi_stop();
438      break;
439    case TW_MT_ARB_LOST: // lost bus arbitration
440      twi_error = TW_MT_ARB_LOST;
441      twi_releaseBus();
442      break;
443
444    // Master Receiver
445    case TW_MR_DATA_ACK: // data received, ack sent
446      // put byte into buffer
447      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
448    case TW_MR_SLA_ACK:  // address sent, ack received
449      // ack if more bytes are expected, otherwise nack
450      if(twi_masterBufferIndex < twi_masterBufferLength){
451        twi_reply(1);
452      }else{
453        twi_reply(0);
454      }
455      break;
456    case TW_MR_DATA_NACK: // data received, nack sent
457      // put final byte into buffer
458      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
459        if (twi_sendStop)
460          twi_stop();
461        else {
462          twi_inRepStart = true;        // we're gonna send the START
463          // don't enable the interrupt. We'll generate the start, but we
464          // avoid handling the interrupt until we're in the next transaction,
465          // at the point where we would normally issue the start.
466          TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ;
467          twi_state = TWI_READY;
468        }   
469        break;
470    case TW_MR_SLA_NACK: // address sent, nack received
471      twi_stop();
472      break;
473    // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case
474
475    // Slave Receiver
476    case TW_SR_SLA_ACK:   // addressed, returned ack
477    case TW_SR_GCALL_ACK: // addressed generally, returned ack
478    case TW_SR_ARB_LOST_SLA_ACK:   // lost arbitration, returned ack
479    case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack
480      // enter slave receiver mode
481      twi_state = TWI_SRX;
482      // indicate that rx buffer can be overwritten and ack
483      twi_rxBufferIndex = 0;
484      twi_reply(1);
485      break;
486    case TW_SR_DATA_ACK:       // data received, returned ack
487    case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack
488      // if there is still room in the rx buffer
489      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
490        // put byte in buffer and ack
491        twi_rxBuffer[twi_rxBufferIndex++] = TWDR;
492        twi_reply(1);
493      }else{
494        // otherwise nack
495        twi_reply(0);
496      }
497      break;
498    case TW_SR_STOP: // stop or repeated start condition received
499      // ack future responses and leave slave receiver state
500      twi_releaseBus();
501      // put a null char after data if there's room
502      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){
503        twi_rxBuffer[twi_rxBufferIndex] = '\0';
504      }
505      // callback to user defined callback
506      twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex);
507      // since we submit rx buffer to "wire" library, we can reset it
508      twi_rxBufferIndex = 0;
509      break;
510    case TW_SR_DATA_NACK:       // data received, returned nack
511    case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack
512      // nack back at master
513      twi_reply(0);
514      break;
515   
516    // Slave Transmitter
517    case TW_ST_SLA_ACK:          // addressed, returned ack
518    case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack
519      // enter slave transmitter mode
520      twi_state = TWI_STX;
521      // ready the tx buffer index for iteration
522      twi_txBufferIndex = 0;
523      // set tx buffer length to be zero, to verify if user changes it
524      twi_txBufferLength = 0;
525      // request for txBuffer to be filled and length to be set
526      // note: user must call twi_transmit(bytes, length) to do this
527      twi_onSlaveTransmit();
528      // if they didn't change buffer & length, initialize it
529      if(0 == twi_txBufferLength){
530        twi_txBufferLength = 1;
531        twi_txBuffer[0] = 0x00;
532      }
533      // transmit first byte from buffer, fall
534    case TW_ST_DATA_ACK: // byte sent, ack returned
535      // copy data to output register
536      TWDR = twi_txBuffer[twi_txBufferIndex++];
537      // if there is more to send, ack, otherwise nack
538      if(twi_txBufferIndex < twi_txBufferLength){
539        twi_reply(1);
540      }else{
541        twi_reply(0);
542      }
543      break;
544    case TW_ST_DATA_NACK: // received nack, we are done
545    case TW_ST_LAST_DATA: // received ack, but we are done already!
546      // ack future responses
547      twi_reply(1);
548      // leave slave receiver state
549      twi_state = TWI_READY;
550      break;
551
552    // All
553    case TW_NO_INFO:   // no state information
554      break;
555    case TW_BUS_ERROR: // bus error, illegal stop/start
556      twi_error = TW_BUS_ERROR;
557      twi_stop();
558      break;
559  }
560}
561
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