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uartsw.c

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/*! \file uartsw.c \brief Software Interrupt-driven UART function library. */
//*****************************************************************************
//
// File Name    : 'uartsw.c'
// Title        : Software Interrupt-driven UART function library
// Author       : Pascal Stang - Copyright (C) 2002-2003
// Created      : 7/20/2002
// Revised      : 6/03/2003
// Version      : 0.1
// Target MCU   : Atmel AVR Series
// Editor Tabs  : 4
//
// 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/interrupt.h>
#include <avr/signal.h>

#include "global.h"
#include "timer.h"
#include "uartsw.h"

// Program ROM constants

// Global variables

// uartsw transmit status and data variables
volatile u08 UartswTxBusy;
volatile u16 UartswBaudRateDiv;
volatile u08 UartswTxData;
volatile u08 UartswTxBitNum;

// receive buffer
cBuffer uartswRxBuffer;               ///< uartsw receive buffer
// automatically allocate space in ram for each buffer
static char uartswRxData[UARTSW_RX_BUFFER_SIZE];
// uartsw receive status and data variables
volatile u08 UartswRxStartBit;
volatile u08 UartswRxData;
volatile u08 UartswRxBitNum;


// functions

//! enable and initialize the software uart
void uartswInit(void)
{
    // initialize the buffers
    uartswInitBuffers();
    // initialize the ports
    sbi(DDRD, 5);
    cbi(DDRD, 6);
    cbi(PORTD, 6);
    // initialize baud rate
    uartswSetBaudRate(9600);
    // set timer prescaler
    timer1SetPrescaler(TIMER_CLK_DIV1);
    // attach TxBit service routine to OC1A
    timerAttach(TIMER1OUTCOMPAREA_INT, uartswTxBitService);
    // attach RxStart service routine to ICP
    timerAttach(TIMER1INPUTCAPTURE_INT, uartswRxBitService);
    // attach RxBit service routine to OC1B
    timerAttach(TIMER1OUTCOMPAREB_INT, uartswRxBitService);
    // enable OC1A interrupt
    sbi(TIMSK, OCIE1A);
    // enable ICP interrupt
    sbi(TIMSK, TICIE1);
    // trigger on rising edge
    sbi(TCCR1B, ICES1);
    // turn on interrupts
    sei();
}

//! create and initialize the uart buffers
void uartswInitBuffers(void)
{
    // initialize the UART receive buffer
    bufferInit(&uartswRxBuffer, uartswRxData, UARTSW_RX_BUFFER_SIZE);
}

//! turns off software UART
void uartswOff(void)
{
    // disable interrupts
    cbi(TIMSK, OCIE1A);
    cbi(TIMSK, OCIE1B);
    cbi(TIMSK, TICIE1);
    // detach the service routines
    timerDetach(TIMER1OUTCOMPAREA_INT);
    timerDetach(TIMER1OUTCOMPAREB_INT);
    timerDetach(TIMER1INPUTCAPTURE_INT);
}

void uartswSetBaudRate(u32 baudrate)
{
    // calculate division factor for requested baud rate, and set it
    UartswBaudRateDiv = (u16)((F_CPU+(baudrate/2L))/(baudrate*1L));
}

//! returns the receive buffer structure 
cBuffer* uartswGetRxBuffer(void)
{
    // return rx buffer pointer
    return &uartswRxBuffer;
}

void uartswSendByte(u08 data)
{
    // wait until uart is ready
    while(UartswTxBusy);
    // set busy flag
    UartswTxBusy = TRUE;
    // save data
    UartswTxData = data;
    // set number of bits (+1 for stop bit)
    UartswTxBitNum = 9;
    
    // set the start bit
    sbi(PORTD, PD5);
    // schedule the next bit
    outw(OCR1A, inw(TCNT1) + UartswBaudRateDiv);
}

//! gets a byte (if available) from the uart receive buffer
u08 uartswReceiveByte(u08* rxData)
{
    // make sure we have a receive buffer
    if(uartswRxBuffer.size)
    {
        // make sure we have data
        if(uartswRxBuffer.datalength)
        {
            // get byte from beginning of buffer
            *rxData = bufferGetFromFront(&uartswRxBuffer);
            return TRUE;
        }
        else
        {
            // no data
            return FALSE;
        }
    }
    else
    {
        // no buffer
        return FALSE;
    }
}

void uartswTxBitService(void)
{
    if(UartswTxBitNum)
    {
        // there are bits still waiting to be transmitted
        if(UartswTxBitNum > 1)
        {
            // transmit data bits (inverted, LSB first)
            if( !(UartswTxData & 0x01) )
                sbi(PORTD, PD5);
            else
                cbi(PORTD, PD5);
            // shift bits down
            UartswTxData = UartswTxData>>1;
        }
        else
        {
            // transmit stop bit
            cbi(PORTD, PD5);
        }
        // schedule the next bit
        outw(OCR1A, inw(OCR1A) + UartswBaudRateDiv);
        // count down
        UartswTxBitNum--;
    }
    else
    {
        // transmission is done
        // clear busy flag
        UartswTxBusy = FALSE;
    }
}

void uartswRxBitService(void)
{
    // this function runs on either:
    // - a rising edge interrupt
    // - OC1B
    if(!UartswRxStartBit)
    {
        // this is a start bit
        // disable ICP interrupt
        cbi(TIMSK, TICIE1);
        // schedule data bit sampling 1.5 bit periods from now
        outw(OCR1B, inw(TCNT1) + UartswBaudRateDiv + UartswBaudRateDiv/2);
        // clear OC1B interrupt flag
        sbi(TIFR, OCF1B);
        // enable OC1B interrupt
        sbi(TIMSK, OCIE1B);
        // set start bit flag
        UartswRxStartBit = TRUE;
        // reset bit counter
        UartswRxBitNum = 0;
        // reset data
        UartswRxData = 0;
    }
    else
    {
        // start bit has already been received
        // we're in the data bits
        
        // shift data byte to make room for new bit
        UartswRxData = UartswRxData>>1;

        // sample the data line
        if( !(inb(PIND) & (1<<6)) )
        {
            // serial line is low
            // record '1' bit (data inverted)
            UartswRxData |= 0x80;
        }

        // increment bit counter
        UartswRxBitNum++;
        // schedule next bit sample
        outw(OCR1B, inw(OCR1B) + UartswBaudRateDiv);

        // check if we have a full byte
        if(UartswRxBitNum >= 8)
        {
            // save data in receive buffer
            bufferAddToEnd(&uartswRxBuffer, UartswRxData);
            // disable OC1B interrupt
            cbi(TIMSK, OCIE1B);
            // clear ICP interrupt flag
            sbi(TIFR, ICF1);
            // enable ICP interrupt
            sbi(TIMSK, TICIE1);
            // clear start bit flag
            UartswRxStartBit = FALSE;
        }
    }
}

/*
void uartswRxBitService(void)
{
    u16 thisBitTime;
    u08 bitperiods;
    u08 i;

    // bit transition was detected
    // record bit's edge time
    thisBitTime = inw(ICR1);

    cbi(PORTB, 0);

    if(!UartswRxStartBit)
    {
        // this is a start bit
        // switch to falling-edge trigger
        cbi(TCCR1B, ICES1);
        // record bit time
        UartswRxBitTime = thisBitTime;
        // set start bit flag
        UartswRxStartBit = TRUE;
        // reset bit counter
        UartswRxBitNum = 0;
        // reset data
        UartswRxData = 0;
    }
    else
    {
        // start bit has already been received
        // we're in the data bits
        
        // how many bit periods since last edge?
        bitperiods = (thisBitTime - UartswRxBitTime + UartswBaudRateDiv/2)/UartswBaudRateDiv;
        // set last edge time
        UartswRxBitTime = thisBitTime;

        if(bitperiods > 10)
        {
            // switch to trigger on rising edge
            sbi(TCCR1B, ICES1);
            // clear start bit flag
            UartswRxStartBit = FALSE;
        }
        else
        {


        if( inb(TCCR1B) & (1<<ICES1) )
        {
            // just triggered on a rising edge
            // previous bits were zero
            // shift in the data (data bits are inverted)
            for(i=0; i<bitperiods; i++)
            {
                UartswRxData = UartswRxData<<1;
                UartswRxData |= 0x01;
            }
            // switch to trigger on falling edge
            cbi(TCCR1B, ICES1);
        }
        else
        {
            // just triggered on a falling edge
            // previous bits were one
            // shift in the data (data bits are inverted)
            for(i=0; i<bitperiods; i++)
            {
                UartswRxData = UartswRxData<<1;
            }
            // switch to trigger on rising edge
            sbi(TCCR1B, ICES1);
        }
        
        // increment bit counter
        UartswRxBitNum += bitperiods;
        
        // check if we have a full byte + start bit
        if(bitperiods > 8)
        {
            // save data in receive buffer
            bufferAddToEnd(&uartswRxBuffer, UartswRxData);
            // switch to trigger on rising edge
            sbi(TCCR1B, ICES1);
            // clear start bit flag
            UartswRxStartBit = FALSE;
        }
        }
    }

    // turn off debug LEDs
    delay(10);
    sbi(PORTB, 0);
    sbi(PORTB, 1);
}
*/

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