/* twi.c - TWI/I2C library for Wiring & Arduino Copyright (c) 2006 Nicholas Zambetti. All right reserved. This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts */ #include #include #include #include #include #include #include "Arduino.h" // for digitalWrite #ifndef cbi #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit)) #endif #ifndef sbi #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit)) #endif #include "pins_arduino.h" #include "twi.h" static volatile uint8_t twi_state; static volatile uint8_t twi_slarw; static volatile uint8_t twi_sendStop; // should the transaction end with a stop static volatile uint8_t twi_inRepStart; // in the middle of a repeated start static void (*twi_onSlaveTransmit)(void); static void (*twi_onSlaveReceive)(uint8_t*, int); static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH]; static volatile uint8_t twi_masterBufferIndex; static volatile uint8_t twi_masterBufferLength; static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH]; static volatile uint8_t twi_txBufferIndex; static volatile uint8_t twi_txBufferLength; static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH]; static volatile uint8_t twi_rxBufferIndex; static volatile uint8_t twi_error; /* * Function twi_init * Desc readys twi pins and sets twi bitrate * Input none * Output none */ void twi_init(void) { // initialize state twi_state = TWI_READY; twi_sendStop = true; // default value twi_inRepStart = false; // activate internal pullups for twi. digitalWrite(SDA, 1); digitalWrite(SCL, 1); // initialize twi prescaler and bit rate cbi(TWSR, TWPS0); cbi(TWSR, TWPS1); TWBR = ((F_CPU / TWI_FREQ) - 16) / 2; /* twi bit rate formula from atmega128 manual pg 204 SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR)) note: TWBR should be 10 or higher for master mode It is 72 for a 16mhz Wiring board with 100kHz TWI */ // enable twi module, acks, and twi interrupt TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA); } /* * Function twi_disable * Desc disables twi pins * Input none * Output none */ void twi_disable(void) { // disable twi module, acks, and twi interrupt TWCR &= ~(_BV(TWEN) | _BV(TWIE) | _BV(TWEA)); // deactivate internal pullups for twi. digitalWrite(SDA, 0); digitalWrite(SCL, 0); } /* * Function twi_slaveInit * Desc sets slave address and enables interrupt * Input none * Output none */ void twi_setAddress(uint8_t address) { // set twi slave address (skip over TWGCE bit) TWAR = address << 1; } /* * Function twi_setClock * Desc sets twi bit rate * Input Clock Frequency * Output none */ void twi_setFrequency(uint32_t frequency) { TWBR = ((F_CPU / frequency) - 16) / 2; /* twi bit rate formula from atmega128 manual pg 204 SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR)) note: TWBR should be 10 or higher for master mode It is 72 for a 16mhz Wiring board with 100kHz TWI */ } /* * Function twi_readFrom * Desc attempts to become twi bus master and read a * series of bytes from a device on the bus * Input address: 7bit i2c device address * data: pointer to byte array * length: number of bytes to read into array * sendStop: Boolean indicating whether to send a stop at the end * Output number of bytes read */ uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sendStop) { uint8_t i; // ensure data will fit into buffer if(TWI_BUFFER_LENGTH < length){ return 0; } // wait until twi is ready, become master receiver while(TWI_READY != twi_state){ continue; } twi_state = TWI_MRX; twi_sendStop = sendStop; // reset error state (0xFF.. no error occured) twi_error = 0xFF; // initialize buffer iteration vars twi_masterBufferIndex = 0; twi_masterBufferLength = length-1; // This is not intuitive, read on... // On receive, the previously configured ACK/NACK setting is transmitted in // response to the received byte before the interrupt is signalled. // Therefor we must actually set NACK when the _next_ to last byte is // received, causing that NACK to be sent in response to receiving the last // expected byte of data. // build sla+w, slave device address + w bit twi_slarw = TW_READ; twi_slarw |= address << 1; if (true == twi_inRepStart) { // if we're in the repeated start state, then we've already sent the start, // (@@@ we hope), and the TWI statemachine is just waiting for the address byte. // We need to remove ourselves from the repeated start state before we enable interrupts, // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning // up. Also, don't enable the START interrupt. There may be one pending from the // repeated start that we sent ourselves, and that would really confuse things. twi_inRepStart = false; // remember, we're dealing with an ASYNC ISR do { TWDR = twi_slarw; } while(TWCR & _BV(TWWC)); TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE); // enable INTs, but not START } else // send start condition TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA); // wait for read operation to complete while(TWI_MRX == twi_state){ continue; } if (twi_masterBufferIndex < length) length = twi_masterBufferIndex; // copy twi buffer to data for(i = 0; i < length; ++i){ data[i] = twi_masterBuffer[i]; } return length; } /* * Function twi_writeTo * Desc attempts to become twi bus master and write a * series of bytes to a device on the bus * Input address: 7bit i2c device address * data: pointer to byte array * length: number of bytes in array * wait: boolean indicating to wait for write or not * sendStop: boolean indicating whether or not to send a stop at the end * Output 0 .. success * 1 .. length to long for buffer * 2 .. address send, NACK received * 3 .. data send, NACK received * 4 .. other twi error (lost bus arbitration, bus error, ..) */ uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait, uint8_t sendStop) { uint8_t i; // ensure data will fit into buffer if(TWI_BUFFER_LENGTH < length){ return 1; } // wait until twi is ready, become master transmitter while(TWI_READY != twi_state){ continue; } twi_state = TWI_MTX; twi_sendStop = sendStop; // reset error state (0xFF.. no error occured) twi_error = 0xFF; // initialize buffer iteration vars twi_masterBufferIndex = 0; twi_masterBufferLength = length; // copy data to twi buffer for(i = 0; i < length; ++i){ twi_masterBuffer[i] = data[i]; } // build sla+w, slave device address + w bit twi_slarw = TW_WRITE; twi_slarw |= address << 1; // if we're in a repeated start, then we've already sent the START // in the ISR. Don't do it again. // if (true == twi_inRepStart) { // if we're in the repeated start state, then we've already sent the start, // (@@@ we hope), and the TWI statemachine is just waiting for the address byte. // We need to remove ourselves from the repeated start state before we enable interrupts, // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning // up. Also, don't enable the START interrupt. There may be one pending from the // repeated start that we sent outselves, and that would really confuse things. twi_inRepStart = false; // remember, we're dealing with an ASYNC ISR do { TWDR = twi_slarw; } while(TWCR & _BV(TWWC)); TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE); // enable INTs, but not START } else // send start condition TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE) | _BV(TWSTA); // enable INTs // wait for write operation to complete while(wait && (TWI_MTX == twi_state)){ continue; } if (twi_error == 0xFF) return 0; // success else if (twi_error == TW_MT_SLA_NACK) return 2; // error: address send, nack received else if (twi_error == TW_MT_DATA_NACK) return 3; // error: data send, nack received else return 4; // other twi error } /* * Function twi_transmit * Desc fills slave tx buffer with data * must be called in slave tx event callback * Input data: pointer to byte array * length: number of bytes in array * Output 1 length too long for buffer * 2 not slave transmitter * 0 ok */ uint8_t twi_transmit(const uint8_t* data, uint8_t length) { uint8_t i; // ensure data will fit into buffer if(TWI_BUFFER_LENGTH < length){ return 1; } // ensure we are currently a slave transmitter if(TWI_STX != twi_state){ return 2; } // set length and copy data into tx buffer twi_txBufferLength = length; for(i = 0; i < length; ++i){ twi_txBuffer[i] = data[i]; } return 0; } /* * Function twi_attachSlaveRxEvent * Desc sets function called before a slave read operation * Input function: callback function to use * Output none */ void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) ) { twi_onSlaveReceive = function; } /* * Function twi_attachSlaveTxEvent * Desc sets function called before a slave write operation * Input function: callback function to use * Output none */ void twi_attachSlaveTxEvent( void (*function)(void) ) { twi_onSlaveTransmit = function; } /* * Function twi_reply * Desc sends byte or readys receive line * Input ack: byte indicating to ack or to nack * Output none */ void twi_reply(uint8_t ack) { // transmit master read ready signal, with or without ack if(ack){ TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA); }else{ TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT); } } /* * Function twi_stop * Desc relinquishes bus master status * Input none * Output none */ void twi_stop(void) { // send stop condition TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO); // wait for stop condition to be exectued on bus // TWINT is not set after a stop condition! while(TWCR & _BV(TWSTO)){ continue; } // update twi state twi_state = TWI_READY; } /* * Function twi_releaseBus * Desc releases bus control * Input none * Output none */ void twi_releaseBus(void) { // release bus TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT); // update twi state twi_state = TWI_READY; } ISR(TWI_vect) { switch(TW_STATUS){ // All Master case TW_START: // sent start condition case TW_REP_START: // sent repeated start condition // copy device address and r/w bit to output register and ack TWDR = twi_slarw; twi_reply(1); break; // Master Transmitter case TW_MT_SLA_ACK: // slave receiver acked address case TW_MT_DATA_ACK: // slave receiver acked data // if there is data to send, send it, otherwise stop if(twi_masterBufferIndex < twi_masterBufferLength){ // copy data to output register and ack TWDR = twi_masterBuffer[twi_masterBufferIndex++]; twi_reply(1); }else{ if (twi_sendStop) twi_stop(); else { twi_inRepStart = true; // we're gonna send the START // don't enable the interrupt. We'll generate the start, but we // avoid handling the interrupt until we're in the next transaction, // at the point where we would normally issue the start. TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ; twi_state = TWI_READY; } } break; case TW_MT_SLA_NACK: // address sent, nack received twi_error = TW_MT_SLA_NACK; twi_stop(); break; case TW_MT_DATA_NACK: // data sent, nack received twi_error = TW_MT_DATA_NACK; twi_stop(); break; case TW_MT_ARB_LOST: // lost bus arbitration twi_error = TW_MT_ARB_LOST; twi_releaseBus(); break; // Master Receiver case TW_MR_DATA_ACK: // data received, ack sent // put byte into buffer twi_masterBuffer[twi_masterBufferIndex++] = TWDR; case TW_MR_SLA_ACK: // address sent, ack received // ack if more bytes are expected, otherwise nack if(twi_masterBufferIndex < twi_masterBufferLength){ twi_reply(1); }else{ twi_reply(0); } break; case TW_MR_DATA_NACK: // data received, nack sent // put final byte into buffer twi_masterBuffer[twi_masterBufferIndex++] = TWDR; if (twi_sendStop) twi_stop(); else { twi_inRepStart = true; // we're gonna send the START // don't enable the interrupt. We'll generate the start, but we // avoid handling the interrupt until we're in the next transaction, // at the point where we would normally issue the start. TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ; twi_state = TWI_READY; } break; case TW_MR_SLA_NACK: // address sent, nack received twi_stop(); break; // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case // Slave Receiver case TW_SR_SLA_ACK: // addressed, returned ack case TW_SR_GCALL_ACK: // addressed generally, returned ack case TW_SR_ARB_LOST_SLA_ACK: // lost arbitration, returned ack case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack // enter slave receiver mode twi_state = TWI_SRX; // indicate that rx buffer can be overwritten and ack twi_rxBufferIndex = 0; twi_reply(1); break; case TW_SR_DATA_ACK: // data received, returned ack case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack // if there is still room in the rx buffer if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){ // put byte in buffer and ack twi_rxBuffer[twi_rxBufferIndex++] = TWDR; twi_reply(1); }else{ // otherwise nack twi_reply(0); } break; case TW_SR_STOP: // stop or repeated start condition received // ack future responses and leave slave receiver state twi_releaseBus(); // put a null char after data if there's room if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){ twi_rxBuffer[twi_rxBufferIndex] = '\0'; } // callback to user defined callback twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex); // since we submit rx buffer to "wire" library, we can reset it twi_rxBufferIndex = 0; break; case TW_SR_DATA_NACK: // data received, returned nack case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack // nack back at master twi_reply(0); break; // Slave Transmitter case TW_ST_SLA_ACK: // addressed, returned ack case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack // enter slave transmitter mode twi_state = TWI_STX; // ready the tx buffer index for iteration twi_txBufferIndex = 0; // set tx buffer length to be zero, to verify if user changes it twi_txBufferLength = 0; // request for txBuffer to be filled and length to be set // note: user must call twi_transmit(bytes, length) to do this twi_onSlaveTransmit(); // if they didn't change buffer & length, initialize it if(0 == twi_txBufferLength){ twi_txBufferLength = 1; twi_txBuffer[0] = 0x00; } // transmit first byte from buffer, fall case TW_ST_DATA_ACK: // byte sent, ack returned // copy data to output register TWDR = twi_txBuffer[twi_txBufferIndex++]; // if there is more to send, ack, otherwise nack if(twi_txBufferIndex < twi_txBufferLength){ twi_reply(1); }else{ twi_reply(0); } break; case TW_ST_DATA_NACK: // received nack, we are done case TW_ST_LAST_DATA: // received ack, but we are done already! // ack future responses twi_reply(1); // leave slave receiver state twi_state = TWI_READY; break; // All case TW_NO_INFO: // no state information break; case TW_BUS_ERROR: // bus error, illegal stop/start twi_error = TW_BUS_ERROR; twi_stop(); break; } }