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linux/drivers/isdn/i4l/isdnhdlc.c
Karsten Keil f3fad223ed ISDN: Fix isdnhdlc for one byte hdlc packets 
Normally HDLC packets contain more as one byte (e.g a X25/X75 header).
But if you use plain HDLC framing, the current code do not encode
1 byte payloads, this patch fix that.

Signed-off-by: Karsten Keil <keil@b1-systems.de>
2009-07-25 20:16:17 +02:00

631 lines
15 KiB
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/*
* isdnhdlc.c -- General purpose ISDN HDLC decoder.
*
* Copyright (C)
* 2009 Karsten Keil <keil@b1-systems.de>
* 2002 Wolfgang Mües <wolfgang@iksw-muees.de>
* 2001 Frode Isaksen <fisaksen@bewan.com>
* 2001 Kai Germaschewski <kai.germaschewski@gmx.de>
*
* 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 <linux/isdn/hdlc.h>
#include <linux/bitrev.h>
/*-------------------------------------------------------------------*/
MODULE_AUTHOR("Wolfgang Mües <wolfgang@iksw-muees.de>, "
"Frode Isaksen <fisaksen@bewan.com>, "
"Kai Germaschewski <kai.germaschewski@gmx.de>");
MODULE_DESCRIPTION("General purpose ISDN HDLC decoder");
MODULE_LICENSE("GPL");
/*-------------------------------------------------------------------*/
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, HDLC_SENDFLAG_ONE
};
void isdnhdlc_rcv_init(struct isdnhdlc_vars *hdlc, u32 features)
{
memset(hdlc, 0, sizeof(struct isdnhdlc_vars));
hdlc->state = HDLC_GET_DATA;
if (features & HDLC_56KBIT)
hdlc->do_adapt56 = 1;
if (features & HDLC_BITREVERSE)
hdlc->do_bitreverse = 1;
}
EXPORT_SYMBOL(isdnhdlc_out_init);
void isdnhdlc_out_init(struct isdnhdlc_vars *hdlc, u32 features)
{
memset(hdlc, 0, sizeof(struct isdnhdlc_vars));
if (features & HDLC_DCHANNEL) {
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;
if (features & HDLC_56KBIT) {
hdlc->do_adapt56 = 1;
hdlc->state = HDLC_SENDFLAG_B0;
} else
hdlc->data_bits = 8;
if (features & HDLC_BITREVERSE)
hdlc->do_bitreverse = 1;
}
EXPORT_SYMBOL(isdnhdlc_rcv_init);
static int
check_frame(struct isdnhdlc_vars *hdlc)
{
int status;
if (hdlc->dstpos < 2) /* too small - framing error */
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;
}
return status;
}
/*
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 u8 *src, int slen,
int *count, u8 *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
};
#define handle_fast_flag(h) \
do {\
if (h->cbin == fast_flag[h->bit_shift]) {\
h->ffvalue = fast_flag_value[h->bit_shift];\
h->state = HDLC_FAST_FLAG;\
h->ffbit_shift = h->bit_shift;\
h->bit_shift = 1;\
} else {\
h->state = HDLC_GET_DATA;\
h->data_received = 0;\
} \
} while (0)
#define handle_abort(h) \
do {\
h->shift_reg = fast_abort[h->ffbit_shift - 1];\
h->hdlc_bits1 = h->ffbit_shift - 2;\
if (h->hdlc_bits1 < 0)\
h->hdlc_bits1 = 0;\
h->data_bits = h->ffbit_shift - 1;\
h->state = HDLC_GET_DATA;\
h->data_received = 0;\
} while (0)
*count = slen;
while (slen > 0) {
if (hdlc->bit_shift == 0) {
/* the code is for bitreverse streams */
if (hdlc->do_bitreverse == 0)
hdlc->cbin = bitrev8(*src++);
else
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) &&
(++hdlc->hdlc_bits1 >= 8) &&
(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)
status = check_frame(hdlc);
hdlc->crc = 0xffff;
hdlc->shift_reg = 0;
hdlc->data_bits = 0;
if (!hdlc->do_adapt56)
handle_fast_flag(hdlc);
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;
hdlc->dstpos = 0;
}
}
hdlc->cbin <<= 1;
hdlc->bit_shift--;
break;
case HDLC_FAST_FLAG:
if (hdlc->cbin == hdlc->ffvalue) {
hdlc->bit_shift = 0;
break;
} else {
if (hdlc->cbin == 0xff) {
hdlc->state = HDLC_FAST_IDLE;
hdlc->bit_shift = 0;
} else if (hdlc->ffbit_shift == 8) {
hdlc->state = HDLC_GETFLAG_B7;
break;
} else
handle_abort(hdlc);
}
break;
default:
break;
}
}
*count -= slen;
return 0;
}
EXPORT_SYMBOL(isdnhdlc_decode);
/*
isdnhdlc_encode - encodes HDLC frames to a transparent bit stream.
The bit stream starts with a beginning flag (01111110). After
that each byte is added to the bit stream with bit stuffing added
(0 after 5 1's).
When the last byte has been removed from the source buffer, the
CRC (2 bytes is added) and the frame terminates with the ending flag.
For the dchannel, the idle character (all 1's) is also added at the end.
If this function is called with empty source buffer (slen=0), flags or
idle character will be generated.
src - source buffer
slen - source buffer length
count - number of bytes removed (encoded) from source buffer
dst _ destination buffer
dsize - destination buffer size
returns - number of encoded bytes in the destination buffer
*/
int isdnhdlc_encode(struct isdnhdlc_vars *hdlc, const u8 *src, u16 slen,
int *count, u8 *dst, int dsize)
{
static const unsigned char xfast_flag_value[] = {
0x7e, 0x3f, 0x9f, 0xcf, 0xe7, 0xf3, 0xf9, 0xfc, 0x7e
};
int len = 0;
*count = slen;
/* special handling for one byte frames */
if ((slen == 1) && (hdlc->state == HDLC_SEND_FAST_FLAG))
hdlc->state = HDLC_SENDFLAG_ONE;
while (dsize > 0) {
if (hdlc->bit_shift == 0) {
if (slen && !hdlc->do_closing) {
hdlc->shift_reg = *src++;
slen--;
if (slen == 0)
/* closing sequence, CRC + flag(s) */
hdlc->do_closing = 1;
hdlc->bit_shift = 8;
} else {
if (hdlc->state == HDLC_SEND_DATA) {
if (hdlc->data_received) {
hdlc->state = HDLC_SEND_CRC1;
hdlc->crc ^= 0xffff;
hdlc->bit_shift = 8;
hdlc->shift_reg =
hdlc->crc & 0xff;
} else if (!hdlc->do_adapt56)
hdlc->state =
HDLC_SEND_FAST_FLAG;
else
hdlc->state =
HDLC_SENDFLAG_B0;
}
}
}
switch (hdlc->state) {
case STOPPED:
while (dsize--)
*dst++ = 0xff;
return dsize;
case HDLC_SEND_FAST_FLAG:
hdlc->do_closing = 0;
if (slen == 0) {
/* the code is for bitreverse streams */
if (hdlc->do_bitreverse == 0)
*dst++ = bitrev8(hdlc->ffvalue);
else
*dst++ = hdlc->ffvalue;
len++;
dsize--;
break;
}
/* fall through */
case HDLC_SENDFLAG_ONE:
if (hdlc->bit_shift == 8) {
hdlc->cbin = hdlc->ffvalue >>
(8 - hdlc->data_bits);
hdlc->state = HDLC_SEND_DATA;
hdlc->crc = 0xffff;
hdlc->hdlc_bits1 = 0;
hdlc->data_received = 1;
}
break;
case HDLC_SENDFLAG_B0:
hdlc->do_closing = 0;
hdlc->cbin <<= 1;
hdlc->data_bits++;
hdlc->hdlc_bits1 = 0;
hdlc->state = HDLC_SENDFLAG_B1A6;
break;
case HDLC_SENDFLAG_B1A6:
hdlc->cbin <<= 1;
hdlc->data_bits++;
hdlc->cbin++;
if (++hdlc->hdlc_bits1 == 6)
hdlc->state = HDLC_SENDFLAG_B7;
break;
case HDLC_SENDFLAG_B7:
hdlc->cbin <<= 1;
hdlc->data_bits++;
if (slen == 0) {
hdlc->state = HDLC_SENDFLAG_B0;
break;
}
if (hdlc->bit_shift == 8) {
hdlc->state = HDLC_SEND_DATA;
hdlc->crc = 0xffff;
hdlc->hdlc_bits1 = 0;
hdlc->data_received = 1;
}
break;
case HDLC_SEND_FIRST_FLAG:
hdlc->data_received = 1;
if (hdlc->data_bits == 8) {
hdlc->state = HDLC_SEND_DATA;
hdlc->crc = 0xffff;
hdlc->hdlc_bits1 = 0;
break;
}
hdlc->cbin <<= 1;
hdlc->data_bits++;
if (hdlc->shift_reg & 0x01)
hdlc->cbin++;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
if (hdlc->bit_shift == 0) {
hdlc->state = HDLC_SEND_DATA;
hdlc->crc = 0xffff;
hdlc->hdlc_bits1 = 0;
}
break;
case HDLC_SEND_DATA:
hdlc->cbin <<= 1;
hdlc->data_bits++;
if (hdlc->hdlc_bits1 == 5) {
hdlc->hdlc_bits1 = 0;
break;
}
if (hdlc->bit_shift == 8)
hdlc->crc = crc_ccitt_byte(hdlc->crc,
hdlc->shift_reg);
if (hdlc->shift_reg & 0x01) {
hdlc->hdlc_bits1++;
hdlc->cbin++;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
} else {
hdlc->hdlc_bits1 = 0;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
}
break;
case HDLC_SEND_CRC1:
hdlc->cbin <<= 1;
hdlc->data_bits++;
if (hdlc->hdlc_bits1 == 5) {
hdlc->hdlc_bits1 = 0;
break;
}
if (hdlc->shift_reg & 0x01) {
hdlc->hdlc_bits1++;
hdlc->cbin++;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
} else {
hdlc->hdlc_bits1 = 0;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
}
if (hdlc->bit_shift == 0) {
hdlc->shift_reg = (hdlc->crc >> 8);
hdlc->state = HDLC_SEND_CRC2;
hdlc->bit_shift = 8;
}
break;
case HDLC_SEND_CRC2:
hdlc->cbin <<= 1;
hdlc->data_bits++;
if (hdlc->hdlc_bits1 == 5) {
hdlc->hdlc_bits1 = 0;
break;
}
if (hdlc->shift_reg & 0x01) {
hdlc->hdlc_bits1++;
hdlc->cbin++;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
} else {
hdlc->hdlc_bits1 = 0;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
}
if (hdlc->bit_shift == 0) {
hdlc->shift_reg = 0x7e;
hdlc->state = HDLC_SEND_CLOSING_FLAG;
hdlc->bit_shift = 8;
}
break;
case HDLC_SEND_CLOSING_FLAG:
hdlc->cbin <<= 1;
hdlc->data_bits++;
if (hdlc->hdlc_bits1 == 5) {
hdlc->hdlc_bits1 = 0;
break;
}
if (hdlc->shift_reg & 0x01)
hdlc->cbin++;
hdlc->shift_reg >>= 1;
hdlc->bit_shift--;
if (hdlc->bit_shift == 0) {
hdlc->ffvalue =
xfast_flag_value[hdlc->data_bits];
if (hdlc->dchannel) {
hdlc->ffvalue = 0x7e;
hdlc->state = HDLC_SEND_IDLE1;
hdlc->bit_shift = 8-hdlc->data_bits;
if (hdlc->bit_shift == 0)
hdlc->state =
HDLC_SEND_FAST_IDLE;
} else {
if (!hdlc->do_adapt56) {
hdlc->state =
HDLC_SEND_FAST_FLAG;
hdlc->data_received = 0;
} else {
hdlc->state = HDLC_SENDFLAG_B0;
hdlc->data_received = 0;
}
/* Finished this frame, send flags */
if (dsize > 1)
dsize = 1;
}
}
break;
case HDLC_SEND_IDLE1:
hdlc->do_closing = 0;
hdlc->cbin <<= 1;
hdlc->cbin++;
hdlc->data_bits++;
hdlc->bit_shift--;
if (hdlc->bit_shift == 0) {
hdlc->state = HDLC_SEND_FAST_IDLE;
hdlc->bit_shift = 0;
}
break;
case HDLC_SEND_FAST_IDLE:
hdlc->do_closing = 0;
hdlc->cbin = 0xff;
hdlc->data_bits = 8;
if (hdlc->bit_shift == 8) {
hdlc->cbin = 0x7e;
hdlc->state = HDLC_SEND_FIRST_FLAG;
} else {
/* the code is for bitreverse streams */
if (hdlc->do_bitreverse == 0)
*dst++ = bitrev8(hdlc->cbin);
else
*dst++ = hdlc->cbin;
hdlc->bit_shift = 0;
hdlc->data_bits = 0;
len++;
dsize = 0;
}
break;
default:
break;
}
if (hdlc->do_adapt56) {
if (hdlc->data_bits == 7) {
hdlc->cbin <<= 1;
hdlc->cbin++;
hdlc->data_bits++;
}
}
if (hdlc->data_bits == 8) {
/* the code is for bitreverse streams */
if (hdlc->do_bitreverse == 0)
*dst++ = bitrev8(hdlc->cbin);
else
*dst++ = hdlc->cbin;
hdlc->data_bits = 0;
len++;
dsize--;
}
}
*count -= slen;
return len;
}
EXPORT_SYMBOL(isdnhdlc_encode);
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