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i2c.c

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/*! \file i2c.c \brief I2C interface using AVR Two-Wire Interface (TWI) hardware. */
//*****************************************************************************
//
// File Name    : 'i2c.c'
// Title        : I2C interface using AVR Two-Wire Interface (TWI) hardware
// Author       : Pascal Stang
// Created      : 2002.06.25
// Revised      : 2002.08.22
// Version      : 0.7
// Target MCU   : Atmel AVR series
// Editor Tabs  : 4
//
// Description : I2C (pronounced "eye-squared-see") is a two-wire bidirectional
//      network designed for easy transfer of information between a wide variety
//      of intelligent devices.  Many of the Atmel AVR series processors have
//      hardware support for transmitting and receiving using an I2C-type bus.
//      In addition to the AVRs, there are thousands of other parts made by
//      manufacturers like Philips, Maxim, National, TI, etc that use I2C as
//      their primary means of communication and control.  Common device types
//      are A/D & D/A converters, temp sensors, intelligent battery monitors,
//      MP3 decoder chips, EEPROM chips, multiplexing switches, etc.
//
//      I2C uses only two wires (SDA and SCL) to communicate bidirectionally
//      between devices.  I2C is a multidrop network, meaning that you can have
//      several devices on a single bus.  Because I2C uses a 7-bit number to
//      identify which device it wants to talk to, you cannot have more than
//      127 devices on a single bus.
//
//      I2C ordinarily requires two 4.7K pull-up resistors to power (one each on
//      SDA and SCL), but for small numbers of devices (maybe 1-4), it is enough
//      to activate the internal pull-up resistors in the AVR processor.  To do
//      this, set the port pins, which correspond to the I2C pins SDA/SCL, high.
//      For example, on the mega163, sbi(PORTC, 0); sbi(PORTC, 1);.
//
//      For complete information about I2C, see the Philips Semiconductor
//      website.  They created I2C and have the largest family of devices that
//      work with I2C.
//
// Note: Many manufacturers market I2C bus devices under a different or generic
//      bus name like "Two-Wire Interface".  This is because Philips still holds
//      "I2C" as a trademark.  For example, SMBus and SMBus devices are hardware
//      compatible and closely related to I2C.  They can be directly connected
//      to an I2C bus along with other I2C devices are are generally accessed in
//      the same way as I2C devices.  SMBus is often found on modern motherboards
//      for temp sensing and other low-level control tasks.
//
// This code is distributed under the GNU Public License
//      which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************

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

#include "i2c.h"

// Standard I2C bit rates are:
// 100KHz for slow speed
// 400KHz for high speed

#define I2C_IDLE                0
#define I2C_BUSY                1
#define I2C_SENT_START          2
#define I2C_SENT_DEVICEADDR     3
#define I2C_SENT_REGADDR        4
#define I2C_SENT_DATA           5

static volatile u08 I2cState;
static u08 I2cDeviceAddrRW;
static u08 I2cData[0x10];
static u08 I2cDataIndex;
static u08 I2cDataLength;

// function pointer to i2c byte receive routine
static void (*i2cSlaveReceive)(u08 data);

// functions
void i2cInit(void)
{
    // set pull-up resistors on I2C bus pins
    sbi(PORTC, 0);  // i2c SCL on ATmega163,323,16,32,etc
    sbi(PORTC, 1);  // i2c SDA on ATmega163,323,16,32,etc
    sbi(PORTD, 0);  // i2c SCL on ATmega128,103,64
    sbi(PORTD, 1);  // i2c SDA on ATmega128,103,64

    // clear SlaveReceive handler to null
    i2cSlaveReceive = 0;
    // set i2c bit rate to 100KHz
    i2cSetBitrate(100);
    // enable TWI (two-wire interface)
    sbi(TWCR, TWEN);
    // set state
    I2cState = I2C_IDLE;
    // enable TWI interrupt and slave address ACK
    sbi(TWCR, TWIE);
    sbi(TWCR, TWEA);
    // enable interrupts
    sei();
}

void i2cSetBitrate(u16 bitrateKHz)
{
    u08 bitrate_div;
    // set i2c bitrate
    // SCL freq = F_CPU/(16+2*TWBR))
    #ifdef TWPS0
        // for processors with additional bitrate division (mega128)
        // SCL freq = F_CPU/(16+2*TWBR*4^TWPS)
        // set TWPS to zero
        cbi(TWSR, TWPS0);
        cbi(TWSR, TWPS1);
    #endif
    // calculate bitrate division   
    bitrate_div = (((F_CPU/1000l)/bitrateKHz)-16)/2;
    //outb(TWBR, bitrate_div);
    outb(TWBR, 0xFF);
}

void i2cSetLocalDeviceAddr(u08 deviceAddr, u08 genCallEn)
{
    // set local device address (used in slave mode only)
    outb(TWAR, ((deviceAddr&0xFE) | (genCallEn?1:0)) );
}

void i2cSetReceiveHandler(void (*i2cRx_func)(u08 data))
{
    i2cSlaveReceive = i2cRx_func;
}

void i2cSend(u08 deviceAddr, u08 length, u08* data)
{
    u08 i;
    // wait for interface to be ready
    while(I2cState);
    // save data
    I2cDeviceAddrRW = (deviceAddr&0xFE);    // RW cleared: write operation
    for(i=0; i<length; i++)
        I2cData[i] = *data++;
    I2cDataIndex = 0;
    I2cDataLength = length;
    // set state
    I2cState = I2C_BUSY;
    // send start condition
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTA));
}

void i2cReceive(u08 deviceAddr, u08 length, u08* data)
{
    u08 i;
    // wait for interface to be ready
    while(I2cState);
    // save data
    I2cDeviceAddrRW = (deviceAddr&0xFE);    // RW set: read operation
    I2cDataIndex = 0;
    I2cDataLength = length;
    // set state
    I2cState = I2C_BUSY;
    // send start condition
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTA));
    // wait for data
    while(I2cState);
    // return data
    for(i=0; i<length; i++)
        *data++ = I2cData[i];
}

//! TWI interrupt service routine
SIGNAL(SIG_2WIRE_SERIAL)
{
    u08 data=0;
    // read status bits
    u08 status = inb(TWSR) & TWSR_STATUS_MASK;

    switch(status)
    {

    // Master General
    case TW_START:                          // 0x08: Sent start condition
        // send device address
        outb(TWDR, I2cDeviceAddrRW);
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
        break;
    case TW_REP_START:                  // 0x10: Sent repeated start condition
        break;
    
    // Master Transmitter & Receiver status codes
    case TW_MT_SLA_ACK:                 // 0x18: Slave address acknowledged
    case TW_MT_DATA_ACK:                    // 0x28: Data acknowledged
        if(I2cDataIndex < I2cDataLength)
        {
            // send data
            outb(TWDR, I2cData[I2cDataIndex++]);
            outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
        }
        else
        {
            // transmit stop condition, enable SLA ACK
            outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTO)|BV(TWEA));
            // set state
            I2cState = I2C_IDLE;
        }
        break;
    case TW_MR_DATA_NACK:               // 0x58: Data received, NACK reply issued
        // store final received data byte
        I2cData[I2cDataIndex++] = inb(TWDR);
        // continue to transmit STOP condition
    case TW_MR_SLA_NACK:                    // 0x48: Slave address not acknowledged
    case TW_MT_SLA_NACK:                    // 0x20: Slave address not acknowledged
    case TW_MT_DATA_NACK:               // 0x30: Data not acknowledged
        // transmit stop condition, enable SLA ACK
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTO)|BV(TWEA));
        // set state
        I2cState = I2C_IDLE;
        break;
    case TW_MT_ARB_LOST:                    // 0x38: Bus arbitration lost
    //case TW_MR_ARB_LOST:              // 0x38: Bus arbitration lost
        // release bus
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
        // set state
        I2cState = I2C_IDLE;
        // release bus and transmit start when bus is free
        //outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTA));
        break;
    case TW_MR_DATA_ACK:                    // 0x50: Data acknowledged
        // store received data byte
        I2cData[I2cDataIndex++] = inb(TWDR);
        // continue to see if more bytes will be received
    case TW_MR_SLA_ACK:                 // 0x40: Slave address acknowledged
        if(I2cDataIndex < (I2cDataLength-1))
            // data byte will be received, reply with ACK (more bytes in transfer)
            outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA));
        else
            // data byte will be received, reply with NACK (final byte in transfer)
            outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
        break;

    // Slave Receiver status codes
    case TW_SR_SLA_ACK:                 // 0x60:
    case TW_SR_ARB_LOST_SLA_ACK:        // 0x68:
    case TW_SR_GCALL_ACK:               // 0x70:
    case TW_SR_ARB_LOST_GCALL_ACK:  // 0x78:
        // receive data byte and return ACK
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA));
        break;
    case TW_SR_DATA_ACK:                    // 0x80:
    case TW_SR_GCALL_DATA_ACK:          // 0x90:
        // get received data byte
        data = inb(TWDR);
        if(i2cSlaveReceive) i2cSlaveReceive(data);
        // receive data byte and return ACK
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA));
        break;
    case TW_SR_DATA_NACK:               // 0x88:
    case TW_SR_GCALL_DATA_NACK:     // 0x98:
        break;
    case TW_SR_STOP:                        // 0xA0:
        // switch to SR mode with SLA ACK
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA));
        // set state
        I2cState = I2C_IDLE;
        break;

    // Slave Transmitter
    case TW_ST_SLA_ACK:                 // 0xA8:
    case TW_ST_ARB_LOST_SLA_ACK:        // 0xB0:
    case TW_ST_DATA_ACK:                    // 0xB8:
    case TW_ST_DATA_NACK:               // 0xC0:
    case TW_ST_LAST_DATA:               // 0xC8:
    // Misc
    case TW_NO_INFO:                        // 0xF8:
    case TW_BUS_ERROR:                  // 0x00:
        break;
    }
}

void i2cSendNI(u08 deviceAddr, u08 length, u08* data)
{
    // disable TWI interrupt
    cbi(TWCR, TWIE);

    // send start condition
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTA));
    while( !(inb(TWCR) & BV(TWINT)) );

    // send device address with write
    outb(TWDR, (deviceAddr&0xFE) );
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
    while( !(inb(TWCR) & BV(TWINT)) );
    
    // send data
    while(length)
    {
        outb(TWDR, *data++);
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
        while( !(inb(TWCR) & BV(TWINT)) );
        length--;
    }
    
    // transmit stop condition
    // leave with TWEA on for slave receiving
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA)|BV(TWSTO));
    // enable TWI interrupt
    sbi(TWCR, TWIE);
}

void i2cReceiveNI(u08 deviceAddr, u08 length, u08 *data)
{
    // disable TWI interrupt
    cbi(TWCR, TWIE);

    // send start condition
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWSTA));
    while( !(inb(TWCR) & BV(TWINT)) );

    // send device address with read
    outb(TWDR, (deviceAddr&0xFE) | 0x01);
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
    while( !(inb(TWCR) & BV(TWINT)) );

    // accept receive data and ack it
    while(length > 1)
    {
        outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA));
        while( !(inb(TWCR) & BV(TWINT)) );
        *data++ = inb(TWDR);
        length--;
    }

    // accept receive data and nack it (last-byte signal)
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT));
    while( !(inb(TWCR) & BV(TWINT)) );
    *data++ = inb(TWDR);

    // transmit stop condition
    // leave with TWEA on for slave receiving
    outb(TWCR, (inb(TWCR)&TWCR_CMD_MASK)|BV(TWINT)|BV(TWEA)|BV(TWSTO));
    // enable TWI interrupt
    sbi(TWCR, TWIE);
}

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