CommandStation-EX/I2CManager_SAMD.h

/*
 *  © 2021, Neil McKechnie. All rights reserved.
 *
 *  This file is part of CommandStation-EX
 *
 *  This is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  It 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef I2CMANAGER_SAMD_H
#define I2CMANAGER_SAMD_H

#include <Arduino.h>
#include "I2CManager.h"

//#include <avr/io.h>
//#include <avr/interrupt.h>

#if defined(I2C_USE_INTERRUPTS) && defined(ARDUINO_SAMD_ZERO)
// PMA - IRQ handler, based on SERCOM3 being used for I2C, as per Arduino Zero & Sparkfun SAMD21
// TODO: test
void SERCOM3_Handler() {
  I2CManagerClass::handleInterrupt();
}
#endif

/***************************************************************************
 *  Set I2C clock speed register.
 ***************************************************************************/
void I2CManagerClass::I2C_setClock(unsigned long i2cClockSpeed) {
  unsigned long temp = ((F_CPU / i2cClockSpeed) - 16) / 2;
  for (uint8_t preScaler = 0; preScaler<=3; preScaler++) {
    if (temp <= 255) {
      TWBR = temp;
      TWSR = (TWSR & 0xfc) | preScaler;
      return;
    } else 
      temp /= 4;
  }
  // Set slowest speed ~= 500 bits/sec
  TWBR = 255;
  TWSR |= 0x03;
}

/***************************************************************************
 *  Initialise I2C registers.
 ***************************************************************************/
void I2CManagerClass::I2C_init()
{
  // PMA - broadly we do the following
  initialise the clock
  initialise the NVIC
  software reset the I2C for the sercom
  set master mode
  do we need smart mode and quick command??
  configure interrupt handlers
  enable interrupts
  set default baud rate
  set SDA/SCL pins as outputs and enable pullups
}

/***************************************************************************
 *  Initiate a start bit for transmission.
 ***************************************************************************/
void I2CManagerClass::I2C_sendStart() {
  bytesToSend = currentRequest->writeLen;
  bytesToReceive = currentRequest->readLen;
  // We may have initiated a stop bit before this without waiting for it.
  // Wait for stop bit to be sent before sending start.
  while (TWCR & (1<<TWSTO)) {}
  TWCR = (1<<TWEN)|ENABLE_TWI_INTERRUPT|(1<<TWINT)|(1<<TWEA)|(1<<TWSTA);  // Send Start
}

/***************************************************************************
 *  Initiate a stop bit for transmission (does not interrupt)
 ***************************************************************************/
void I2CManagerClass::I2C_sendStop() {
  TWDR = 0xff;  // Default condition = SDA released
  TWCR = (1<<TWEN)|(1<<TWINT)|(1<<TWEA)|(1<<TWSTO);  // Send Stop
}

/***************************************************************************
 *  Close I2C down
 ***************************************************************************/
void I2CManagerClass::I2C_close() {
  // disable TWI
  I2C_sendStop();
  while (TWCR & (1<<TWSTO)) {}
  TWCR = (1<<TWINT);                 // clear any interrupt and stop twi.
}

/***************************************************************************
 *  Main state machine for I2C, called from interrupt handler or,
 *  if I2C_USE_INTERRUPTS isn't defined, from the I2CManagerClass::loop() function
 *  (and therefore, indirectly, from I2CRB::wait() and I2CRB::isBusy()).
 ***************************************************************************/
void I2CManagerClass::I2C_handleInterrupt() {
  if (!(TWCR & (1<<TWINT))) return;  // Nothing to do.

  uint8_t twsr = TWSR & 0xF8;

  // Cases are ordered so that the most frequently used ones are tested first.
  switch (twsr) {
    case TWI_MTX_DATA_ACK:      // Data byte has been transmitted and ACK received
    case TWI_MTX_ADR_ACK:       // SLA+W has been transmitted and ACK received
      if (bytesToSend) {  // Send first.
        if (operation == OPERATION_SEND_P)
          TWDR = GETFLASH(currentRequest->writeBuffer + (txCount++));
        else
          TWDR = currentRequest->writeBuffer[txCount++];
        bytesToSend--;
        TWCR = (1<<TWEN)|ENABLE_TWI_INTERRUPT|(1<<TWINT)|(1<<TWEA);
      } else if (bytesToReceive) {  // All sent, anything to receive?
        while (TWCR & (1<<TWSTO)) {}    // Wait for stop to be sent
        TWCR = (1<<TWEN)|ENABLE_TWI_INTERRUPT|(1<<TWINT)|(1<<TWEA)|(1<<TWSTA);  // Send Start
      } else {  // Nothing left to send or receive
        TWDR = 0xff;  // Default condition = SDA released
        TWCR = (1<<TWEN)|(1<<TWINT)|(1<<TWEA)|(1<<TWSTO);  // Send Stop
        state = I2C_STATUS_OK;
      }
      break;
    case TWI_MRX_DATA_ACK:      // Data byte has been received and ACK transmitted
      if (bytesToReceive > 0) {
        currentRequest->readBuffer[rxCount++] = TWDR;
        bytesToReceive--;
      }
      /* fallthrough */
    case TWI_MRX_ADR_ACK:      // SLA+R has been sent and ACK received
      if (bytesToReceive <= 1) {
        TWCR = (1<<TWEN)|ENABLE_TWI_INTERRUPT|(1<<TWINT); // Send NACK after next reception
      } else {
        // send ack
        TWCR = (1<<TWEN)|ENABLE_TWI_INTERRUPT|(1<<TWINT)|(1<<TWEA);
      }
      break;
    case TWI_MRX_DATA_NACK:     // Data byte has been received and NACK transmitted
      if (bytesToReceive > 0) {
        currentRequest->readBuffer[rxCount++] = TWDR;
        bytesToReceive--;
      }
      TWCR = (1<<TWEN)|(1<<TWINT)|(1<<TWEA)|(1<<TWSTO);  // Send Stop
      state = I2C_STATUS_OK;
      break;
    case TWI_START:             // START has been transmitted  
    case TWI_REP_START:         // Repeated START has been transmitted
      // Set up address and R/W
      if (operation == OPERATION_READ || (operation==OPERATION_REQUEST && !bytesToSend))
        TWDR = (currentRequest->i2cAddress << 1) | 1; // SLA+R
      else
        TWDR = (currentRequest->i2cAddress << 1) | 0; // SLA+W
      TWCR = (1<<TWEN)|ENABLE_TWI_INTERRUPT|(1<<TWINT)|(1<<TWEA);
      break;
    case TWI_MTX_ADR_NACK:      // SLA+W has been transmitted and NACK received
    case TWI_MRX_ADR_NACK:      // SLA+R has been transmitted and NACK received
    case TWI_MTX_DATA_NACK:     // Data byte has been transmitted and NACK received
      TWDR = 0xff;  // Default condition = SDA released
      TWCR = (1<<TWEN)|(1<<TWINT)|(1<<TWEA)|(1<<TWSTO);  // Send Stop
      state = I2C_STATUS_NEGATIVE_ACKNOWLEDGE;
      break;
    case TWI_ARB_LOST:          // Arbitration lost
      // Restart transaction from start.
      I2C_sendStart();
      break;
    case TWI_BUS_ERROR:         // Bus error due to an illegal START or STOP condition
    default:
      TWDR = 0xff;  // Default condition = SDA released
      TWCR = (1<<TWEN)|(1<<TWINT)|(1<<TWEA)|(1<<TWSTO);  // Send Stop
      state = I2C_STATUS_TRANSMIT_ERROR;
  }
}

#if defined(I2C_USE_INTERRUPTS)
ISR(TWI_vect) {
  I2CManagerClass::handleInterrupt();
}
#endif

#endif /* I2CMANAGER_AVR_H */