/*******************************************************************************

FILE NAME: rfmodem.c



Copyright 1999-2000 SAGE Telecommunications Pty Ltd

All rights Reserved

The information contained herein is confidential property of the company. The

use, copying, transfer or disclosure of such information is prohibited except

by express written agreement with the Company.

Permission is hereby granted to use this software for non-commercial purposes.



AUTHOR: Rod Egan from SAGE Telecommunications Pty Ltd

	http://www.sages.com.au

DESCRIPTION:

	RF modem packet rx/tx routines



REVISION HISTORY:

        0.0    11-Dec-99    initial source

	0.1    12-May-00    released for private use

*******************************************************************************/





#include "picreg.h"



#fuses HS,NOPROTECT,WDT

#zero_ram

#use delay(clock=4000000, RESTART_WDT )



#define BUF_SIZE 32



// 5mSec of chars at 2400 ( 10 bits per char ~= 4.2mSec per char

#define PREAMBLE_LEN 4

#define PREAMBLE 0xaa



// rx uart sync delay in mSec ( 2 char times )

#define SYNC_DELAY 9

#define HDR1 0x55

#define HDR2 0xaa



// postamble in mSec

#define POSTAMBLE 1



// rx delay loops are ~12uSec

// wait for 1st char 100mSec

#define PREAMBLE_DLY 8500



// delay between chars after preamble ~1.5 char times 6mSec

#define INTERCHAR_DLY 500



enum OPM

{

    MS_MODE, PKT_MODE, STATS_MODE,

    LAST_MODE

}op_mode;





/* global variable storage */

byte buffer[ BUF_SIZE ];

byte buf_len;

byte cksm;

byte rx_len;





/* global prototypes declaration */



/* local prototypes declaration */

byte get_packet( void );

void send_packet( void );



/****************************************************************************/

/* modem receive packet routine                                             */

/*  Receive encapsulated packet                                             */

/*  entry: na                                                               */

/*  exit:  True is packet rx'd ok with data in buffer                       */

/*         else                                                             */

/*         False if timeout or error                                        */

/****************************************************************************/





byte get_packet( void )

{

    short status = FALSE;

    short got_hdr1 = FALSE;

    short got_hdr2 = FALSE;



    byte *ptr;



    byte c;

    long timeout;



    timeout = PREAMBLE_DLY;



        // wait for 1st header char

    do

    {

        if( kbhit() )

        {

            if( getc() == HDR1 )

            {

                got_hdr1 = TRUE;

                timeout = PREAMBLE_DLY;

                break;

            }

        }

    }while( --timeout );



        // if we have 1st char then wait for 2nd header char

    if( got_hdr1 )

    {

        do

        {

            if( kbhit() )

            {

                c = getc();

                if( c == HDR2 )

                {

                        // got 2nd header so flag and exit

                    got_hdr2 = TRUE;

                    timeout = INTERCHAR_DLY;

                    break;

                }

                else if( c == HDR1 )

                {

                    // another chance at rx'ing 1st header

                    timeout = PREAMBLE_DLY;

                }

            }

        }while( --timeout );

    }



        // if rx'd 2nd header then get len byte

    if( got_hdr2 )

    {

        do

        {

            if( kbhit() )

            {

                cksm = buf_len = rx_len = getc();

                    // got len byte, abort if absurd value

                if( buf_len <= sizeof( buffer ) )

                {

                        // got len and it's ok now get data

                    ptr = buffer;

                    timeout = INTERCHAR_DLY;

                    do

                    {

                        if( kbhit() )

                        {

                            c = getc();

                            *ptr++ = c;

                            cksm ^= c;

                            timeout = INTERCHAR_DLY;

                            if( !(--rx_len ) )

                                break;

                        }

                    }while( --timeout );

                        // if got all rx data then check CRC

                    if( !rx_len )

                    {

                        do

                        {

                            if( kbhit() )

                            {

                                if( cksm == getc() )

                                {

                                        // crc ok, so flag and exit

                                    status = TRUE;

                                }

                                    // break anyway even if bad CRC

                                break;

                            }

                        }while( --timeout );

                    }

                }

                break;

            }

        }while( --timeout );

    }

    return( status );

}



/****************************************************************************/

/* modem send packet routine                                                */

/*  Encapsulate packet buffer and send to RF modem                          */

/*  entry: na                                                               */

/*  exit:  na                                                               */

/****************************************************************************/

void send_packet( void )

{

    byte i, c;



    byte *ptr;

    

        // send preamble to help sync rx module data slicer

    i = PREAMBLE_LEN;

    do

    {

        putc( PREAMBLE );

    }while( --i );

    restart_wdt();

        // send a continual 'high' for ~2 char periods to allow RX uart to sync

    io_portb.tx_m = TRUE;

    delay_ms( SYNC_DELAY );

    restart_wdt();

        // send data packet header, lenght byte then data

    putc( HDR1 );

    putc( HDR2 );

    putc( buf_len );

        // seed checksum with data length

    cksm = i = buf_len;

    ptr = buffer;

    do

    {

        c = *ptr++;

        putc( c );

        cksm ^= c;

    }while( --i );

        // send checksum

    putc( cksm );

        // make sure Tx is turned off

    io_portb.tx_m = FALSE;

    sent_count++;

}



/* end of file rfmodem.c */