Colony

/* @file i2c.c

 * @brief

 * In the case where you have master sends and then a master request to the same

 * address, you will not give up control of the line because the send and

 * request addresses are seen as different addresses. In between it will send a

 * restart but will not give up the line.

 *

 * @author CMU Robotics Club, Kevin Woo, Sursh Nidhiry

 * @bug Not tested.

 */

#include <avr/interrupt.h>

#include <util/twi.h>

#include "i2c.h"

#include "ring_buffer.h"

/**

 * @defgroup i2c I2C 

 *

 * @brief Provides Inter-Interconnected-Communications (I2C)

 * 

 * Initiates I2C functions on an ATMega128 which has a fully hardware Two Wire 

 * Interface (TWI) module. Any Atmel chip with this hardware should be able to

 * use the software.

 *

 * This code will operate in a multi-master enviornment and can be either a

 * slave or a master at any time (as long as they are not one or the other at

 * the moment. You can queue up multiple transmission modes in the buffer up to 

 * the buffer size. The buffer is implemented as a ring buffer.

 *

 * It is implemented using callback functions. Whenever you want to send a packet

 * you can call the built in send function (as a master) and it will send an array

 * of bytes. Master recieve and slave send/receive are all handled by the call back

 * functions. It is up to the end user to create functions that will handle the

 * receiving of packets. Their functions will be called with every byte recieved

 * so you must either buffer the inputs or handle each one separately.

 *

 * On errors we will simply flush the entire buffer.

 * 

 * For information on how I2C operates, read the wikipedia article

 * http://en.wikipedia.org/wiki/I2c

 * for a good explanation of how it works.

 * @{

 */

/** 

 * @brief Set bit rate 12 = 100kbit/s (max speed setting is 10 for an

 *  8 MHz clock). It is a divider, so the lower the number the faster the speed.

 */

#define I2C_BIT_RATE_DIVIDER 0x0C

static int start_flag;

static fun_mrecv_t master_recv_function;

static fun_srecv_t slave_recv_function;

static fun_send_t slave_send_function;

RING_BUFFER_NEW(i2c_buffer, 128, char, i2c_write_buff, i2c_addr_buff);

/**

 * @brief Initializes the i2c module.

 *

 * Initializes the I2C module to start listening on the i2c lines. If the callback functions

 * are not set to null they will be called when that transmission mode is called. The address

 * is your address that you will listen to when you are not the master.

 *

 * @param addr 			Your address on the I2C bus.

 * @param master_recv 	The address of the function to call when you receive a byte when you are a

 *                    	master.

 * @param slave_recv 	The address of the function to call when you are a slave you receive data

 *								from the master

 * @param slave_send		The address of the function to call when you are a slave and the master

 *								requests data from you.

 **/

int i2c_init(char addr, fun_mrecv_t master_recv, fun_srecv_t slave_recv, fun_send_t slave_send) {

    master_recv_function = master_recv;

    slave_recv_function = slave_recv;

    slave_send_function = slave_send;

    RING_BUFFER_CLEAR(i2c_write_buff);

    RING_BUFFER_CLEAR(i2c_addr_buff);

    /* enables twi interrupt, automatic ack sending, and all twi hardware */

    TWCR =  (_BV(TWEA) | _BV(TWEN) | _BV(TWIE));

    /* sets the bit rate of data transmission */

    TWBR = I2C_BIT_RATE_DIVIDER;

    /* sets the address (it is stored in the 7 most significant bits) and allows

     * global messages to be accepted */

    TWAR = (addr << 1) | 1;

    return 0;

}

/**

 * @brief Sends a byte array over I2C as a master

 *

 * Will perform a send over I2C to the destination from data for the ammount of

 * bytes that bytes is.

 *

 * @param dest		Destination address of the data on the I2C bus.

 * @param data 	The pointer to the byte array of data

 * @param bytes	The amount of bytes long that the byte array is. This is how

 *						many bytes from the array that the function will send.

 **/

int i2c_send(char dest, char *data, size_t bytes) {

    int i;

    /* adding data to be sent to ring buffers is not atomic,

     * so disable interrupts */

    cli();

    for(i = 0; i < bytes; i++) {

        if(RING_BUFFER_FULL(i2c_write_buff)) {

            sei();

            return -1;

        }

        RING_BUFFER_ADD(i2c_write_buff, data[i]);

        RING_BUFFER_ADD(i2c_addr_buff, dest << 1);

    }

    /* re-enable the interrupts */

    sei();

    /* send the start bit, only if this device is not currently master */

    if(!start_flag) {

        start_flag = 1;

        TWCR |= _BV(TWSTA);

        TWCR |= _BV(TWINT);

    }

    return 0;

}

/**

 * @brief Send a master request to the destination

 *

 * Sends a request of data from the target address and calls

 * the callback function to handle data as it comes in. This function will

 * not work if the slave has not informationt to send or has nothing implemented

 * to send it.

 *

 * @param dest		The destination that we want to receive information from.

 **/ 

int i2c_request(char dest) {

    if(RING_BUFFER_FULL(i2c_write_buff))

        return -1;

    RING_BUFFER_ADD(i2c_write_buff, 0);

    RING_BUFFER_ADD(i2c_addr_buff, (dest << 1) | 1);

    if(!start_flag) {

        start_flag = 1;

        TWCR |= _BV(TWSTA);

        TWCR |= _BV(TWINT);

    }

    return 0;

}

/**

 * @brief Interrupt to handle I2C interrupts from the I2C hardware.

 * 

 * Uses the status codes from the I2C register to handle the events

 * needed to advance in I2C stages. For instance, you will get a bit for

 * receiving a start ack, then a address ack, then a data ack, etc.

 * The events are handled in each switch case. The status codes are defined

 * by avr-gcc in /util/twi.h but are the same codes as the Atmel documentation.

 *

 * Bytes are sent by popping off the ring buffer. It also will keep track

 * of what modes the send is in.

 *

 * Errors are handled here as well.

 **/ 

 /* @} */

ISR(TWI_vect) {

	static char data_to_send;

	static char addr_to_send = -1;

	char addr, statusCode;

	//Get status code (only upper 5 bits)

	statusCode = (TWSR & 0xF8);

    switch (statusCode) {

        //Start sent successfully

        case TW_START:

        case TW_REP_START:

            /* Send address and write

             * ring_buffer will not be empty */

            RING_BUFFER_REMOVE(i2c_addr_buff, addr_to_send);

            RING_BUFFER_REMOVE(i2c_write_buff, data_to_send);

            /* first send the address */

            TWDR = addr_to_send; 

            //Turn off start bits

            TWCR &= ~_BV(TWSTA);

            break;

        //Master Transmit - Address sent succesfully

        case TW_MT_SLA_ACK:

        //Send byte

            TWDR = data_to_send;

            PORTG &= ~_BV(PG2);

            break;

        //Master Transmit - Data sent succesfully

        case TW_MT_DATA_ACK:    

            //If there is still data to send

            if(!RING_BUFFER_EMPTY(i2c_write_buff)) {

                RING_BUFFER_PEEK(i2c_addr_buff, addr);

                //Still data for this address

                if (addr == addr_to_send) {

                    RING_BUFFER_REMOVE(i2c_addr_buff, addr);

                    RING_BUFFER_REMOVE(i2c_write_buff, TWDR);

                    break;

                //No more data for this address, data for another address -> resend start

                } else {

                    TWCR |= _BV(TWSTA);

                    break;

                }

            }

            /* there are no bytes to send */

            TWCR |= _BV(TWSTO);

            start_flag = 0;

            break; 

        //Master Transmit - Slave sends a nack, transmit is done

        case TW_MT_DATA_NACK:

            PORTG |= _BV(PG2);

            TWCR |= _BV(TWSTO);

            start_flag = 0;

            break;

        //Master Receive - Address sent succesfully

        case TW_MR_SLA_ACK:

            PORTG |= _BV(PG2);

            break;

        //Master Receive - Data received succesfully

        case TW_MR_DATA_ACK:

            if(master_recv_function) {

                if(!master_recv_function(TWDR)) {

                    TWCR &= ~_BV(TWEA);

                }

            }

            break;

        //Master Receive - Slave sends a nack, transmission is done    

        case TW_MR_DATA_NACK:

            TWCR |= _BV(TWEA);

            //If there is still data to send

            if(!RING_BUFFER_EMPTY(i2c_write_buff)) {

                TWCR |= _BV(TWSTA);

                break;

            }

            /* there are no bytes to send */

            TWCR |= _BV(TWSTO);

            start_flag = 0;  

            break;

        //Slave Transmit - Address received

        case TW_ST_SLA_ACK:

            break;

        //Slave Transmit - Nack received, no data requsted

        case TW_ST_DATA_NACK:

            break;

        //Slave Transmit - Data requested, ack received

        case TW_ST_DATA_ACK:

            if (slave_send_function) {

                TWDR = slave_send_function();

            }

            break;

        //Slave Receive - Address received  

        case TW_SR_SLA_ACK:

            break;

        //Slave Receive - Data received, ack returned

        case TW_SR_DATA_ACK:

            if(slave_recv_function) {

                slave_recv_function(TWDR);

            }

            break;

        //Stop sent  

        case TW_SR_STOP:

            break;

        //Problem on the bus, reset everything

        default:

            TWCR |= _BV(TWSTO);

            start_flag = 0;

            RING_BUFFER_CLEAR(i2c_write_buff);

            RING_BUFFER_CLEAR(i2c_addr_buff);  	

    }

  /* Toggle TWINT so that it resets and executes the commands */

  TWCR |= _BV(TWINT);

}