Cnomicon/src/libPIC/pkt_recv.c

/*****************************************************************************
 * Copyright (C) 2008
 * ProbeStar Telematics, LLC
 * All Rights Reserved.  Proprietary and Confidential.
 *============================================================================
 * Packet Receive
 *----------------------------------------------------------------------------
 * Details
*****************************************************************************/

/*****************************************************************************
 * includes
*****************************************************************************/

#include "system.h"
#include "delay.h"
#include "types.h"
#include "serial.h"
#include "packet.h"

/*****************************************************************************
 * defines
*****************************************************************************/

/*****************************************************************************
 * macros
*****************************************************************************/

/*****************************************************************************
 * structs & typedefs
*****************************************************************************/

/*****************************************************************************
 * global constants
*****************************************************************************/

/*****************************************************************************
 * global variables
*****************************************************************************/

/*****************************************************************************
 * static constants
*****************************************************************************/

/*****************************************************************************
 * static variables
*****************************************************************************/

/*****************************************************************************
 * static prototypes
*****************************************************************************/

/*****************************************************************************
 * C functions
*****************************************************************************/

///////////////////////////////////////////////////////////////////////////////
// de-Packetizer
///////////////////////////////////////////////////////////////////////////////

void recvClear( BYTE n )
{
	// clear buffer till end of current packet
	n++;
	while ( n-- && getchavail() )
		getch();
}

void recvFlush( void )
{
	// flush queue
	SerialClear();
}

int recvGet( BYTE n )
{
	int c;
	BYTE i;
	UINT t;
	DWORD v = 0;

	for ( i = 0; i < n; i++ )
	{
		t = TIMEOUT;
		if ( ( c = getchtimeout( &t ) ) < 0 )
			return PACKET_ERR_TIMEOUT;
		v |= ( c << ( i * 8 ) );
	}
	return v;
}

int recvWait( UINT iWait )
{
	iWait /= 10;

	// wait for a packet
	while ( iWait-- )
	{
		if ( getchavail() > 0 )
			return 1;
		DelayUsec( 100 );
	}
	return 0;
}

int recvHeader( WORD *pwCheck, WORD *pwId, BYTE *pbyFlag )
{
	int c = 0;
	WORD n = 0;
	UINT t;

	// software timeouts
	// check if line needs to turn around
	if ( dirRadio( RADIO_LISTEN ) )
	{
		// generous wait for a packet
		if ( !recvWait( PACKET_WAIT_TIME ) )
			return PACKET_ERR_TIMEOUT;
	}
	else
	{
		// wait for next packet
		if ( !recvWait( PACKET_WAIT_TIME/2 ) )
			return PACKET_ERR_TIMEOUT;
	}

	// wait till synchronization string
	while ( n < PACKET_SYNC_LENGTH )
	{
		t = TIMEOUT;
		c = getchtimeout( &t );

		if ( c == PACKET_RECV_SYNC )
		{
			if ( n < PACKET_SYNC_LENGTH - 1 )
				n++;
		}
		else if ( c == PACKET_SYNC_CHAR )
		{
			if ( n == PACKET_SYNC_LENGTH - 1 )
				n++;
			else
				n = 0;
		}
		else if ( c < 0 )
			return c;
		else
			n = 0;
	}

#ifdef PACKET_FILTER
	// got it
	if ( g_byPacketAvail )
		g_byPacketAvail--;
#endif
	// init checksum or CRC
	*pwCheck = 0;

	// id
	*pwId = (WORD) recvGet( PACKET_ID_SIZE );

	// flag byte
	*pbyFlag = (BYTE) recvGet( PACKET_FL_SIZE );

	// byte count
	n = (WORD) recvGet( PACKET_BC_SIZE );

	// check flag
	if ( *pbyFlag )
	{
		// check control flag bits
		if ( *pbyFlag & PACKET_FLAG_STREAM )
			return n;	// ignore rest of bits used for streaming counter

		// check each flag
		if ( *pbyFlag & PACKET_FLAG_CRC )
			g_bPacketCRC = 1;
	}

	return n;
}

int recvByte( WORD *pwCheck )
{
	UINT t = TIMEOUT;
	int c;

	if ( ( c = getchtimeout( &t ) ) < 0 )
		return c;

	if ( g_bPacketCRC )
		*pwCheck = doCRC16( *pwCheck, c );
	else
		*pwCheck += (BYTE) c;
	return (BYTE) c;
}

int recvData( WORD *pwCheck, PKTBANK BYTE * pbyData, WORD nBytes, WORD maxBytes )
{
	WORD nRead = 0;
	UINT t;
	int c;

	// read bytes
	while ( nBytes-- )
	{
		// read
		t = TIMEOUT;
		c = getchtimeout( &t );
		if ( c < 0 )
			return c;

		// store data away
		if ( pbyData && ( nRead < maxBytes ) )
			*pbyData++ = c;

		// CRC or checksum
		if ( g_bPacketCRC )
			*pwCheck = doCRC16( *pwCheck, c );
		else
			*pwCheck += (BYTE) c;

		// count
		nRead++;
	}

	return nRead;
}

int recvTrailer( WORD *pwCheck )
{
	UINT t = TIMEOUT;
	WORD wCheck;
	int c;

	if ( ( c = getchtimeout( &t ) ) < 0 )
		return c;

	// CRC or checksum
	if ( g_bPacketCRC )
	{
		// low byte
		wCheck = c;
		// high byte
		if ( ( c = getchtimeout( &t ) ) < 0 )
			return c;
		wCheck |= (c << 8);

		// compare CRCs
		if ( *pwCheck != wCheck )
			return 0;
	}
	else
	{
		// byte, masked
		*pwCheck += (BYTE) c;
		*pwCheck &= 0xff;

		// good checksum is zero
		if ( *pwCheck )
			return 0;
	}
	return 1;
}

int recvPacket( WORD *pwId, PKTBANK BYTE *pbyPacket, BYTE *pbyFlag, WORD maxBytes )
{
	WORD wCheck;
	int nBytes;

	// header
	if ( ( nBytes = recvHeader( &wCheck, pwId, pbyFlag ) ) < 0 )
		return nBytes;

	// check
	if ( nBytes > maxBytes )
		return PACKET_BUF_TOOBIG;

	// data
	if ( ( nBytes = recvData( &wCheck, pbyPacket, (WORD)nBytes, (WORD)maxBytes ) ) < 0 )
		return nBytes;

	// checksum
	if ( recvTrailer( &wCheck ) )
		return nBytes;
	return PACKET_BAD_CHECKSUM;
}

int recvFinish( WORD nBytes )
{
	WORD wCheck;

	recvData( &wCheck, NULL, nBytes, nBytes );
	if ( recvTrailer( &wCheck ) )
		return nBytes;
	return PACKET_BAD_CHECKSUM;
}