uart.c

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/*! \file uart.c \brief UART driver with buffer support. */
// *****************************************************************************
//
// File Name    : 'uart.c'
// Title        : UART driver with buffer support
// Author       : Pascal Stang - Copyright (C) 2000-2002
// Created      : 11/22/2000
// Revised      : 06/09/2003
// Version      : 1.3
// 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 "buffer.h"
#include "uart.h"

// UART global variables
// flag variables
volatile u08   uartReadyTx;         ///< uartReadyTx flag
volatile u08   uartBufferedTx;      ///< uartBufferedTx flag
// receive and transmit buffers
cBuffer uartRxBuffer;               ///< uart receive buffer
cBuffer uartTxBuffer;               ///< uart transmit buffer
unsigned short uartRxOverflow;      ///< receive overflow counter

#ifndef UART_BUFFERS_EXTERNAL_RAM
    // using internal ram,
    // automatically allocate space in ram for each buffer
    static char uartRxData[UART_RX_BUFFER_SIZE];
    static char uartTxData[UART_TX_BUFFER_SIZE];
#endif

typedef void (*voidFuncPtru08)(unsigned char);
volatile static voidFuncPtru08 UartRxFunc;

// enable and initialize the uart
void uartInit(void)
{
    // initialize the buffers
    uartInitBuffers();
    // initialize user receive handler
    UartRxFunc = 0;

    // enable RxD/TxD and interrupts
    outb(UCR, BV(RXCIE)|BV(TXCIE)|BV(RXEN)|BV(TXEN));

    // set default baud rate
    uartSetBaudRate(UART_DEFAULT_BAUD_RATE);  
    // initialize states
    uartReadyTx = TRUE;
    uartBufferedTx = FALSE;
    // clear overflow count
    uartRxOverflow = 0;
    // enable interrupts
    sei();
}

// create and initialize the uart transmit and receive buffers
void uartInitBuffers(void)
{
    #ifndef UART_BUFFERS_EXTERNAL_RAM
        // initialize the UART receive buffer
        bufferInit(&uartRxBuffer, uartRxData, UART_RX_BUFFER_SIZE);
        // initialize the UART transmit buffer
        bufferInit(&uartTxBuffer, uartTxData, UART_TX_BUFFER_SIZE);
    #else
        // initialize the UART receive buffer
        bufferInit(&uartRxBuffer, (u08*) UART_RX_BUFFER_ADDR, UART_RX_BUFFER_SIZE);
        // initialize the UART transmit buffer
        bufferInit(&uartTxBuffer, (u08*) UART_TX_BUFFER_ADDR, UART_TX_BUFFER_SIZE);
    #endif
}

// redirects received data to a user function
void uartSetRxHandler(void (*rx_func)(unsigned char c))
{
    // set the receive interrupt to run the supplied user function
    UartRxFunc = rx_func;
}

// set the uart baud rate
void uartSetBaudRate(u32 baudrate)
{
    // calculate division factor for requested baud rate, and set it
    u16 bauddiv = ((F_CPU+(baudrate*8L))/(baudrate*16L)-1);
    outb(UBRRL, bauddiv);
    #ifdef UBRRH
    outb(UBRRH, bauddiv>>8);
    #endif
}

// returns the receive buffer structure 
cBuffer* uartGetRxBuffer(void)
{
    // return rx buffer pointer
    return &uartRxBuffer;
}

// returns the transmit buffer structure 
cBuffer* uartGetTxBuffer(void)
{
    // return tx buffer pointer
    return &uartTxBuffer;
}

// transmits a byte over the uart
void uartSendByte(u08 txData)
{
    // wait for the transmitter to be ready
    while(!uartReadyTx);
    // send byte
    outb(UDR, txData);
    // set ready state to FALSE
    uartReadyTx = FALSE;
}

// gets a single byte from the uart receive buffer (getchar-style)
int uartGetByte(void)
{
    u08 c;
    if(uartReceiveByte(&c))
        return c;
    else
        return -1;
}

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

// flush all data out of the receive buffer
void uartFlushReceiveBuffer(void)
{
    // flush all data from receive buffer
    //bufferFlush(&uartRxBuffer);
    // same effect as above
    uartRxBuffer.datalength = 0;
}

// return true if uart receive buffer is empty
u08 uartReceiveBufferIsEmpty(void)
{
    if(uartRxBuffer.datalength == 0)
    {
        return TRUE;
    }
    else
    {
        return FALSE;
    }
}

// add byte to end of uart Tx buffer
u08 uartAddToTxBuffer(u08 data)
{
    // add data byte to the end of the tx buffer
    return bufferAddToEnd(&uartTxBuffer, data);
}

// start transmission of the current uart Tx buffer contents
void uartSendTxBuffer(void)
{
    // turn on buffered transmit
    uartBufferedTx = TRUE;
    // send the first byte to get things going by interrupts
    uartSendByte(bufferGetFromFront(&uartTxBuffer));
}
/*
// transmit nBytes from buffer out the uart
u08 uartSendBuffer(char *buffer, u16 nBytes)
{
    register u08 first;
    register u16 i;

    // check if there's space (and that we have any bytes to send at all)
    if((uartTxBuffer.datalength + nBytes < uartTxBuffer.size) && nBytes)
    {
        // grab first character
        first = *buffer++;
        // copy user buffer to uart transmit buffer
        for(i = 0; i < nBytes-1; i++)
        {
            // put data bytes at end of buffer
            bufferAddToEnd(&uartTxBuffer, *buffer++);
        }

        // send the first byte to get things going by interrupts
        uartBufferedTx = TRUE;
        uartSendByte(first);
        // return success
        return TRUE;
    }
    else
    {
        // return failure
        return FALSE;
    }
}
*/
// UART Transmit Complete Interrupt Handler
UART_INTERRUPT_HANDLER(SIG_UART_TRANS)
{
    // check if buffered tx is enabled
    if(uartBufferedTx)
    {
        // check if there's data left in the buffer
        if(uartTxBuffer.datalength)
        {
            // send byte from top of buffer
            outb(UDR, bufferGetFromFront(&uartTxBuffer));
        }
        else
        {
            // no data left
            uartBufferedTx = FALSE;
            // return to ready state
            uartReadyTx = TRUE;
        }
    }
    else
    {
        // we're using single-byte tx mode
        // indicate transmit complete, back to ready
        uartReadyTx = TRUE;
    }
}

// UART Receive Complete Interrupt Handler
UART_INTERRUPT_HANDLER(SIG_UART_RECV)
{
    u08 c;
    
    // get received char
    c = inb(UDR);

    // if there's a user function to handle this receive event
    if(UartRxFunc)
    {
        // call it and pass the received data
        UartRxFunc(c);
    }
    else
    {
        // otherwise do default processing
        // put received char in buffer
        // check if there's space
        if( !bufferAddToEnd(&uartRxBuffer, c) )
        {
            // no space in buffer
            // count overflow
            uartRxOverflow++;
        }
    }
}

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