isdnhdlc.c

linux-2.6.15.6

/*
 * isdnhdlc.c  --  General purpose ISDN HDLC decoder.
 *
 *Copyright (C) 2002	Wolfgang M黣s      <[e-mail]>
 *		2001 	Frode Isaksen      <[e-mail]>
 *              2001 	Kai Germaschewski  <[e-mail]>
 *
 *      This program is free software; you can redistribute it and/or modify
 *      it under the terms of the GNU General Public License as published by
 *      the Free Software Foundation; either version 2 of the License, or
 *      (at your option) any later version.
 *
 *      This program is distributed in the hope that it will be useful,
 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *      GNU General Public License for more details.
 *
 *      You should have received a copy of the GNU General Public License
 *      along with this program; if not, write to the Free Software
 *      Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/crc-ccitt.h>
#include "isdnhdlc.h"

/*-------------------------------------------------------------------*/

MODULE_AUTHOR("Wolfgang M黣s <[e-mail]>, "
	      "Frode Isaksen <[e-mail]>, "
	      "Kai Germaschewski <[e-mail]>");
MODULE_DESCRIPTION("General purpose ISDN HDLC decoder");
MODULE_LICENSE("GPL");

/*-------------------------------------------------------------------*/

/* bit swap table.
 * Very handy for devices with different bit order,
 * and neccessary for each transparent B-channel access for all
 * devices which works with this HDLC decoder without bit reversal.
 */
const unsigned char isdnhdlc_bit_rev_tab[256] = {
	0x00,0x80,0x40,0xC0,0x20,0xA0,0x60,0xE0,0x10,0x90,0x50,0xD0,0x30,0xB0,0x70,0xF0,
	0x08,0x88,0x48,0xC8,0x28,0xA8,0x68,0xE8,0x18,0x98,0x58,0xD8,0x38,0xB8,0x78,0xF8,
	0x04,0x84,0x44,0xC4,0x24,0xA4,0x64,0xE4,0x14,0x94,0x54,0xD4,0x34,0xB4,0x74,0xF4,
	0x0C,0x8C,0x4C,0xCC,0x2C,0xAC,0x6C,0xEC,0x1C,0x9C,0x5C,0xDC,0x3C,0xBC,0x7C,0xFC,
	0x02,0x82,0x42,0xC2,0x22,0xA2,0x62,0xE2,0x12,0x92,0x52,0xD2,0x32,0xB2,0x72,0xF2,
	0x0A,0x8A,0x4A,0xCA,0x2A,0xAA,0x6A,0xEA,0x1A,0x9A,0x5A,0xDA,0x3A,0xBA,0x7A,0xFA,
	0x06,0x86,0x46,0xC6,0x26,0xA6,0x66,0xE6,0x16,0x96,0x56,0xD6,0x36,0xB6,0x76,0xF6,
	0x0E,0x8E,0x4E,0xCE,0x2E,0xAE,0x6E,0xEE,0x1E,0x9E,0x5E,0xDE,0x3E,0xBE,0x7E,0xFE,
	0x01,0x81,0x41,0xC1,0x21,0xA1,0x61,0xE1,0x11,0x91,0x51,0xD1,0x31,0xB1,0x71,0xF1,
	0x09,0x89,0x49,0xC9,0x29,0xA9,0x69,0xE9,0x19,0x99,0x59,0xD9,0x39,0xB9,0x79,0xF9,
	0x05,0x85,0x45,0xC5,0x25,0xA5,0x65,0xE5,0x15,0x95,0x55,0xD5,0x35,0xB5,0x75,0xF5,
	0x0D,0x8D,0x4D,0xCD,0x2D,0xAD,0x6D,0xED,0x1D,0x9D,0x5D,0xDD,0x3D,0xBD,0x7D,0xFD,
	0x03,0x83,0x43,0xC3,0x23,0xA3,0x63,0xE3,0x13,0x93,0x53,0xD3,0x33,0xB3,0x73,0xF3,
	0x0B,0x8B,0x4B,0xCB,0x2B,0xAB,0x6B,0xEB,0x1B,0x9B,0x5B,0xDB,0x3B,0xBB,0x7B,0xFB,
	0x07,0x87,0x47,0xC7,0x27,0xA7,0x67,0xE7,0x17,0x97,0x57,0xD7,0x37,0xB7,0x77,0xF7,
	0x0F,0x8F,0x4F,0xCF,0x2F,0xAF,0x6F,0xEF,0x1F,0x9F,0x5F,0xDF,0x3F,0xBF,0x7F,0xFF
};

enum {
	HDLC_FAST_IDLE,HDLC_GET_FLAG_B0,HDLC_GETFLAG_B1A6,HDLC_GETFLAG_B7,
	HDLC_GET_DATA,HDLC_FAST_FLAG
};

enum {
	HDLC_SEND_DATA,HDLC_SEND_CRC1,HDLC_SEND_FAST_FLAG,
	HDLC_SEND_FIRST_FLAG,HDLC_SEND_CRC2,HDLC_SEND_CLOSING_FLAG,
	HDLC_SEND_IDLE1,HDLC_SEND_FAST_IDLE,HDLC_SENDFLAG_B0,
	HDLC_SENDFLAG_B1A6,HDLC_SENDFLAG_B7,STOPPED
};

void isdnhdlc_rcv_init (struct isdnhdlc_vars *hdlc, int do_adapt56)
{
   	hdlc->bit_shift = 0;
	hdlc->hdlc_bits1 = 0;
	hdlc->data_bits = 0;
	hdlc->ffbit_shift = 0;
	hdlc->data_received = 0;
	hdlc->state = HDLC_GET_DATA;
	hdlc->do_adapt56 = do_adapt56;
	hdlc->dchannel = 0;
	hdlc->crc = 0;
	hdlc->cbin = 0;
	hdlc->shift_reg = 0;
	hdlc->ffvalue = 0;
	hdlc->dstpos = 0;
}

void isdnhdlc_out_init (struct isdnhdlc_vars *hdlc, int is_d_channel, int do_adapt56)
{
   	hdlc->bit_shift = 0;
	hdlc->hdlc_bits1 = 0;
	hdlc->data_bits = 0;
	hdlc->ffbit_shift = 0;
	hdlc->data_received = 0;
	hdlc->do_closing = 0;
	hdlc->ffvalue = 0;
	if (is_d_channel) {
		hdlc->dchannel = 1;
		hdlc->state = HDLC_SEND_FIRST_FLAG;
	} else {
		hdlc->dchannel = 0;
		hdlc->state = HDLC_SEND_FAST_FLAG;
		hdlc->ffvalue = 0x7e;
	}
	hdlc->cbin = 0x7e;
	hdlc->bit_shift = 0;
	if(do_adapt56){
		hdlc->do_adapt56 = 1;
		hdlc->data_bits = 0;
		hdlc->state = HDLC_SENDFLAG_B0;
	} else {
		hdlc->do_adapt56 = 0;
		hdlc->data_bits = 8;
	}
	hdlc->shift_reg = 0;
}

/*
  isdnhdlc_decode - decodes HDLC frames from a transparent bit stream.

  The source buffer is scanned for valid HDLC frames looking for
  flags (01111110) to indicate the start of a frame. If the start of
  the frame is found, the bit stuffing is removed (0 after 5 1's).
  When a new flag is found, the complete frame has been received
  and the CRC is checked.
  If a valid frame is found, the function returns the frame length
  excluding the CRC with the bit HDLC_END_OF_FRAME set.
  If the beginning of a valid frame is found, the function returns
  the length.
  If a framing error is found (too many 1s and not a flag) the function
  returns the length with the bit HDLC_FRAMING_ERROR set.
  If a CRC error is found the function returns the length with the
  bit HDLC_CRC_ERROR set.
  If the frame length exceeds the destination buffer size, the function
  returns the length with the bit HDLC_LENGTH_ERROR set.

  src - source buffer
  slen - source buffer length
  count - number of bytes removed (decoded) from the source buffer
  dst _ destination buffer
  dsize - destination buffer size
  returns - number of decoded bytes in the destination buffer and status
  flag.
 */
int isdnhdlc_decode (struct isdnhdlc_vars *hdlc, const unsigned char *src,
		     int slen, int *count, unsigned char *dst, int dsize)
{
	int status=0;

	static const unsigned char fast_flag[]={
		0x00,0x00,0x00,0x20,0x30,0x38,0x3c,0x3e,0x3f
	};

	static const unsigned char fast_flag_value[]={
		0x00,0x7e,0xfc,0xf9,0xf3,0xe7,0xcf,0x9f,0x3f
	};

	static const unsigned char fast_abort[]={
		0x00,0x00,0x80,0xc0,0xe0,0xf0,0xf8,0xfc,0xfe,0xff
	};

	*count = slen;

	while(slen > 0){
		if(hdlc->bit_shift==0){
			hdlc->cbin = *src++;
			slen--;
			hdlc->bit_shift = 8;
			if(hdlc->do_adapt56){
				hdlc->bit_shift --;
			}
		}

		switch(hdlc->state){
		case STOPPED:
			return 0;
		case HDLC_FAST_IDLE:
			if(hdlc->cbin == 0xff){
				hdlc->bit_shift = 0;
				break;
			}
			hdlc->state = HDLC_GET_FLAG_B0;
			hdlc->hdlc_bits1 = 0;
			hdlc->bit_shift = 8;
			break;
		case HDLC_GET_FLAG_B0:
			if(!(hdlc->cbin & 0x80)) {
				hdlc->state = HDLC_GETFLAG_B1A6;
				hdlc->hdlc_bits1 = 0;
			} else {
				if(!hdlc->do_adapt56){
					if(++hdlc->hdlc_bits1 >=8 ) if(hdlc->bit_shift==1)
						hdlc->state = HDLC_FAST_IDLE;
				}
			}
			hdlc->cbin<<=1;
			hdlc->bit_shift --;
			break;
		case HDLC_GETFLAG_B1A6:
			if(hdlc->cbin & 0x80){
				hdlc->hdlc_bits1++;
				if(hdlc->hdlc_bits1==6){
					hdlc->state = HDLC_GETFLAG_B7;
				}
			} else {
				hdlc->hdlc_bits1 = 0;
			}
			hdlc->cbin<<=1;
			hdlc->bit_shift --;
			break;
		case HDLC_GETFLAG_B7:
			if(hdlc->cbin & 0x80) {
				hdlc->state = HDLC_GET_FLAG_B0;
			} else {
				hdlc->state = HDLC_GET_DATA;
				hdlc->crc = 0xffff;
				hdlc->shift_reg = 0;
				hdlc->hdlc_bits1 = 0;
				hdlc->data_bits = 0;
				hdlc->data_received = 0;
			}
			hdlc->cbin<<=1;
			hdlc->bit_shift --;
			break;
		case HDLC_GET_DATA:
			if(hdlc->cbin & 0x80){
				hdlc->hdlc_bits1++;
				switch(hdlc->hdlc_bits1){
				case 6:
					break;
				case 7:
					if(hdlc->data_received) {
						// bad frame
						status = -HDLC_FRAMING_ERROR;
					}
					if(!hdlc->do_adapt56){
						if(hdlc->cbin==fast_abort[hdlc->bit_shift+1]){
							hdlc->state = HDLC_FAST_IDLE;
							hdlc->bit_shift=1;
							break;
						}
					} else {
						hdlc->state = HDLC_GET_FLAG_B0;
					}
					break;
				default:
					hdlc->shift_reg>>=1;
					hdlc->shift_reg |= 0x80;
					hdlc->data_bits++;
					break;
				}
			} else {
				switch(hdlc->hdlc_bits1){
				case 5:
					break;
				case 6:
					if(hdlc->data_received){
						if (hdlc->dstpos < 2) {
							status = -HDLC_FRAMING_ERROR;
						} else if (hdlc->crc != 0xf0b8){
							// crc error
							status = -HDLC_CRC_ERROR;
						} else {
							// remove CRC
							hdlc->dstpos -= 2;
							// good frame
							status = hdlc->dstpos;
						}
					}
					hdlc->crc = 0xffff;
					hdlc->shift_reg = 0;
					hdlc->data_bits = 0;
					if(!hdlc->do_adapt56){
						if(hdlc->cbin==fast_flag[hdlc->bit_shift]){
							hdlc->ffvalue = fast_flag_value[hdlc->bit_shift];
							hdlc->state = HDLC_FAST_FLAG;
							hdlc->ffbit_shift = hdlc->bit_shift;
							hdlc->bit_shift = 1;
						} else {
							hdlc->state = HDLC_GET_DATA;
							hdlc->data_received = 0;
						}
					} else {
						hdlc->state = HDLC_GET_DATA;
						hdlc->data_received = 0;
					}
					break;
				default:
					hdlc->shift_reg>>=1;
					hdlc->data_bits++;
					break;
				}
				hdlc->hdlc_bits1 = 0;
			}
			if (status) {
				hdlc->dstpos = 0;
				*count -= slen;
				hdlc->cbin <<= 1;
				hdlc->bit_shift--;
				return status;
			}
			if(hdlc->data_bits==8){
				hdlc->data_bits = 0;
				hdlc->data_received = 1;
				hdlc->crc = crc_ccitt_byte(hdlc->crc, hdlc->shift_reg);

				// good byte received
				if (hdlc->dstpos < dsize) {
					dst[hdlc->dstpos++] = hdlc->shift_reg;
				} else {
					// frame too long
					status = -HDLC_LENGTH_ERROR;