/*
* Copyright (c) 2006 Nokia Corporation and/or its subsidiary(-ies).
* All rights reserved.
* This component and the accompanying materials are made available
* under the terms of "Eclipse Public License v1.0"
* which accompanies this distribution, and is available
* at the URL "http://www.eclipse.org/legal/epl-v10.html".
*
* Initial Contributors:
* Nokia Corporation - initial contribution.
*
* Contributors:
*
* Description: 
*
*	Frame Check Sequence checksums (FCS) for 16 and 32 bits.
*
*	The 16-bit version uses a 512-byte table (2 bytes * 256 elements)
*	and the 32-bit version uses a 1024-byte table (4 bytes * 256 elements)
*
*	Serial-based HDLC-like framing (RFC 1662) for use with the
*	CWDS serial protocol.
*	
*	Serial data is transmitted using an HDLC-like framing convention.
*	Byte-oriented streams are transmitted with a starting frame byte
*	and also followed by an ending frame byte and a checksum (FCS).
*	
*	Errors can be detected with high probability using the FCS.
*	While this is not intended to be used in an environment that
*	generates a large number of errors, nevertheless it can be
*	useful to help ensure that packets arrive with a high degree of
*	certainty and to allow data to be dropped and still allow
*	continuous data.
*	
*	Sender and receiver can be resynchronized with the receipt of a new
*	framing byte.
*	
*	
*	Frame Format
*	
*	The general frame format specified in RFC 1662 is described as:
*
*		+----------+----------+----------+
*		|   Flag   | Address  | Control  |
*		| 01111110 | 11111111 | 00000011 |
*		+----------+----------+----------+
*		+----------+-------------+---------+
*		| Protocol | Information | Padding |
*		| 8/16 bits|      *      |    *    |
*		+----------+-------------+---------+
*		+----------+----------+-----------------
*		|   FCS    |   Flag   | Inter-frame Fill
*		|16/32 bits| 01111110 | or next Address
*		+----------+----------+-----------------
*
*	The routines in this file use a subset and are not negotiated;
*	they are simply assumed. These are:
*	
*	Address and Control Field Compression is always ON.
*	Protocol Field Compression is always ON.
*	Protocol value is implied, but undefined.
*	Padding is OFF.
*	MRU is 1500 bytes.
*	FCS is 32 bits.
*	Trailing Flag is always transmitted.
*	
*	
*	The resulting frame format is:
*
*		+----------+
*		|   Flag   |
*		| 01111110 |
*		+----------+
*		+-------------+
*		| Information |
*		|      *      |
*		+-------------+
*		+----------+----------+-----------------
*		|   FCS    |   Flag   | Inter-frame Fill
*		|16/32 bits| 01111110 | or next Address
*		+----------+----------+-----------------
*	
*	Macros & Typedefs
*		
*		FCSBITSIZE
*		
*			This header file must first define FCSBITSIZE to be either one of:
*			FCS16 or FCS32.  These control the definitions for the rest of the header
*			file and the underlying tables.  Selecting FCS16 will cause the header
*			file to define 16-bit types, table, and functions for calculating the
*			16-bit FCS.  Selecting FCS32 is identical, except it uses 32-bit FCS values.
*			
*			FCS16 will use 512 bytes (2 bytes * 256 entries) of constant data space.
*			FCS32 will use 1024 bytes.
*	
*		FCSType
*		
*			The 16- or 32-bit type used for the FCS register and datum.
*
*		PPPINITFCS
*			
*			Initialize the FCS register with this value.
*		
*		PPPGOODFCS
*		
*			On the receiver side, after the FCS compute function is applied
*			to all data bytes plus the two or four FCS bytes, the correct FCS
*			value will be PPPGOODFCS, a constant.
*		
*		PPPCOMPFCS
*
*
*	REFERENCES
*
*	[RFC1662.94]	Simpson, W., Editor, "PPP in HDLC-like Framing,"
*					STD 51, RFC 1662, Daydreamer, July 1994.
*
*/
	
	
#ifndef TRK_SERFRAME_H
#define TRK_SERFRAME_H

#define FCS8  0					/* SCM: Added for simple 8-bit checksums */
#define FCS16 1
#define FCS32 2

#define	FCSBITSIZE FCS8			/* define as either FCS8, FCS16 or FCS32 */


#if FCSBITSIZE == FCS8

	/*
	 *	Definitions for 8-bit simple Frame Check Sequences
	 */
	 
	typedef unsigned char FCSType;	/* 8-bit type */

	#define PPPINITFCS8		0x00		/* Initial FCS value */
	#define PPPGOODFCS8		0xFF		/* Good final FCS value */

	#define PPPINITFCS		PPPINITFCS8
	#define PPPGOODFCS		PPPGOODFCS8
	#define PPPCOMPFCS		0xFF		/* complement FCS value */

	#ifdef __cplusplus	
		inline FCSType PPPFCS(FCSType fcs, unsigned char c)
		{
			return (fcs + c);
		}

	#else
		#define PPPFCS(fcs, c)	(fcs + c)
	#endif

	
#elif FCSBITSIZE == FCS16

	/*
	 *	Definitions for 16-bit Frame Check Sequences
	 */
	 
	typedef unsigned short FCSType;	/* 16-bit type */
/*	extern FCSType fcstab[]; */
	extern const FCSType fcstab[256];

	#define PPPINITFCS16	0xffff		/* Initial FCS value */
	#define PPPGOODFCS16	0xf0b8		/* Good final FCS value */

	#define PPPINITFCS		PPPINITFCS16
	#define PPPGOODFCS		PPPGOODFCS16
	#define PPPCOMPFCS		0xffff		/* complement FCS value */

	#if __cplusplus	
		inline FCSType PPPFCS(FCSType fcs, unsigned char c)
		{
			return (((fcs) >> 8) ^ fcstab[((fcs) ^ (c)) & 0xff]);
		}

	#else
		#define PPPFCS(fcs, c)	(((fcs) >> 8) ^ fcstab[((fcs) ^ (c)) & 0xff])
	#endif

#elif FCSBITSIZE == FCS32

	/*
	 *	Definitions for 32-bit Frame Check Sequences
	 */

	typedef unsigned long FCSType;	/* 32-bit FCS */
/*	extern FCSType fcstab_32[]; */
	extern const FCSType fcstab_32[256];

	#define PPPINITFCS32 	0xffffffff	/* Initial FCS value */
	#define PPPGOODFCS32 	0xdebb20e3	/* Good final FCS value */

	#define PPPINITFCS		PPPINITFCS32
	#define PPPGOODFCS		PPPGOODFCS32
	#define PPPCOMPFCS		0xffffffff	/* complement FCS value */
	
	#if __cplusplus
		inline FCSType PPPFCS(FCSType fcs, unsigned char c)
		{
			return (((fcs) >> 8) ^ fcstab_32[((fcs) ^ (c)) & 0xff]);
		}
	#else
		#define PPPFCS(fcs, c) (((fcs) >> 8) ^ fcstab_32[((fcs) ^ (c)) & 0xff])
	#endif

#endif


/****************************************************************************/
/*
 *	Constants used for framing serial data
 */
/****************************************************************************/

#define	PPP_UI			0x03	/* Unnumbered Information */
#define	PPP_FLAG		0x7e	/* Flag Sequence */
#define	PPP_ESCAPE		0x7d	/* Asynchronous Control Escape */
#define	PPP_TRANS		0x20	/* Asynchronous transparency modifier */

#define MAXFRAMESIZE	0x1000	/* maximum unframed/unescaped data size */

#endif /* ndef TRK_SERFRAME_H */