drivers/isdn/i4l/isdnhdlc.c

   1 /*
   2  * isdnhdlc.c  --  General purpose ISDN HDLC decoder.
   3  *
   4  * Copyright (C)
   5  *      2009    Karsten Keil            <keil@b1-systems.de>
   6  *      2002    Wolfgang Mües          <wolfgang@iksw-muees.de>
   7  *      2001    Frode Isaksen           <fisaksen@bewan.com>
   8  *      2001    Kai Germaschewski       <kai.germaschewski@gmx.de>
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License as published by
  12  * the Free Software Foundation; either version 2 of the License, or
  13  * (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License
  21  * along with this program; if not, write to the Free Software
  22  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  23  */
  24
  25 #include <linux/module.h>
  26 #include <linux/init.h>
  27 #include <linux/crc-ccitt.h>
  28 #include <linux/isdn/hdlc.h>
  29 #include <linux/bitrev.h>
  30
  31 /*-------------------------------------------------------------------*/
  32
  33 MODULE_AUTHOR("Wolfgang Mües <wolfgang@iksw-muees.de>, "
  34               "Frode Isaksen <fisaksen@bewan.com>, "
  35               "Kai Germaschewski <kai.germaschewski@gmx.de>");
  36 MODULE_DESCRIPTION("General purpose ISDN HDLC decoder");
  37 MODULE_LICENSE("GPL");
  38
  39 /*-------------------------------------------------------------------*/
  40
  41 enum {
  42         HDLC_FAST_IDLE, HDLC_GET_FLAG_B0, HDLC_GETFLAG_B1A6, HDLC_GETFLAG_B7,
  43         HDLC_GET_DATA, HDLC_FAST_FLAG
  44 };
  45
  46 enum {
  47         HDLC_SEND_DATA, HDLC_SEND_CRC1, HDLC_SEND_FAST_FLAG,
  48         HDLC_SEND_FIRST_FLAG, HDLC_SEND_CRC2, HDLC_SEND_CLOSING_FLAG,
  49         HDLC_SEND_IDLE1, HDLC_SEND_FAST_IDLE, HDLC_SENDFLAG_B0,
  50         HDLC_SENDFLAG_B1A6, HDLC_SENDFLAG_B7, STOPPED, HDLC_SENDFLAG_ONE
  51 };
  52
  53 void isdnhdlc_rcv_init(struct isdnhdlc_vars *hdlc, u32 features)
  54 {
  55         memset(hdlc, 0, sizeof(struct isdnhdlc_vars));
  56         hdlc->state = HDLC_GET_DATA;
  57         if (features & HDLC_56KBIT)
  58                 hdlc->do_adapt56 = 1;
  59         if (features & HDLC_BITREVERSE)
  60                 hdlc->do_bitreverse = 1;
  61 }
  62 EXPORT_SYMBOL(isdnhdlc_out_init);
  63
  64 void isdnhdlc_out_init(struct isdnhdlc_vars *hdlc, u32 features)
  65 {
  66         memset(hdlc, 0, sizeof(struct isdnhdlc_vars));
  67         if (features & HDLC_DCHANNEL) {
  68                 hdlc->dchannel = 1;
  69                 hdlc->state = HDLC_SEND_FIRST_FLAG;
  70         } else {
  71                 hdlc->dchannel = 0;
  72                 hdlc->state = HDLC_SEND_FAST_FLAG;
  73                 hdlc->ffvalue = 0x7e;
  74         }
  75         hdlc->cbin = 0x7e;
  76         if (features & HDLC_56KBIT) {
  77                 hdlc->do_adapt56 = 1;
  78                 hdlc->state = HDLC_SENDFLAG_B0;
  79         } else
  80                 hdlc->data_bits = 8;
  81         if (features & HDLC_BITREVERSE)
  82                 hdlc->do_bitreverse = 1;
  83 }
  84 EXPORT_SYMBOL(isdnhdlc_rcv_init);
  85
  86 static int
  87 check_frame(struct isdnhdlc_vars *hdlc)
  88 {
  89         int status;
  90
  91         if (hdlc->dstpos < 2)   /* too small - framing error */
  92                 status = -HDLC_FRAMING_ERROR;
  93         else if (hdlc->crc != 0xf0b8)   /* crc error */
  94                 status = -HDLC_CRC_ERROR;
  95         else {
  96                 /* remove CRC */
  97                 hdlc->dstpos -= 2;
  98                 /* good frame */
  99                 status = hdlc->dstpos;
 100         }
 101         return status;
 102 }
 103
 104 /*
 105   isdnhdlc_decode - decodes HDLC frames from a transparent bit stream.
 106
 107   The source buffer is scanned for valid HDLC frames looking for
 108   flags (01111110) to indicate the start of a frame. If the start of
 109   the frame is found, the bit stuffing is removed (0 after 5 1's).
 110   When a new flag is found, the complete frame has been received
 111   and the CRC is checked.
 112   If a valid frame is found, the function returns the frame length
 113   excluding the CRC with the bit HDLC_END_OF_FRAME set.
 114   If the beginning of a valid frame is found, the function returns
 115   the length.
 116   If a framing error is found (too many 1s and not a flag) the function
 117   returns the length with the bit HDLC_FRAMING_ERROR set.
 118   If a CRC error is found the function returns the length with the
 119   bit HDLC_CRC_ERROR set.
 120   If the frame length exceeds the destination buffer size, the function
 121   returns the length with the bit HDLC_LENGTH_ERROR set.
 122
 123   src - source buffer
 124   slen - source buffer length
 125   count - number of bytes removed (decoded) from the source buffer
 126   dst _ destination buffer
 127   dsize - destination buffer size
 128   returns - number of decoded bytes in the destination buffer and status
 129   flag.
 130  */
 131 int isdnhdlc_decode(struct isdnhdlc_vars *hdlc, const u8 *src, int slen,
 132         int *count, u8 *dst, int dsize)
 133 {
 134         int status = 0;
 135
 136         static const unsigned char fast_flag[] = {
 137                 0x00, 0x00, 0x00, 0x20, 0x30, 0x38, 0x3c, 0x3e, 0x3f
 138         };
 139
 140         static const unsigned char fast_flag_value[] = {
 141                 0x00, 0x7e, 0xfc, 0xf9, 0xf3, 0xe7, 0xcf, 0x9f, 0x3f
 142         };
 143
 144         static const unsigned char fast_abort[] = {
 145                 0x00, 0x00, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe, 0xff
 146         };
 147
 148 #define handle_fast_flag(h) \
 149         do {\
 150                 if (h->cbin == fast_flag[h->bit_shift]) {\
 151                         h->ffvalue = fast_flag_value[h->bit_shift];\
 152                         h->state = HDLC_FAST_FLAG;\
 153                         h->ffbit_shift = h->bit_shift;\
 154                         h->bit_shift = 1;\
 155                 } else {\
 156                         h->state = HDLC_GET_DATA;\
 157                         h->data_received = 0;\
 158                 } \
 159         } while (0)
 160
 161 #define handle_abort(h) \
 162         do {\
 163                 h->shift_reg = fast_abort[h->ffbit_shift - 1];\
 164                 h->hdlc_bits1 = h->ffbit_shift - 2;\
 165                 if (h->hdlc_bits1 < 0)\
 166                         h->hdlc_bits1 = 0;\
 167                 h->data_bits = h->ffbit_shift - 1;\
 168                 h->state = HDLC_GET_DATA;\
 169                 h->data_received = 0;\
 170         } while (0)
 171
 172         *count = slen;
 173
 174         while (slen > 0) {
 175                 if (hdlc->bit_shift == 0) {
 176                         /* the code is for bitreverse streams */
 177                         if (hdlc->do_bitreverse == 0)
 178                                 hdlc->cbin = bitrev8(*src++);
 179                         else
 180                                 hdlc->cbin = *src++;
 181                         slen--;
 182                         hdlc->bit_shift = 8;
 183                         if (hdlc->do_adapt56)
 184                                 hdlc->bit_shift--;
 185                 }
 186
 187                 switch (hdlc->state) {
 188                 case STOPPED:
 189                         return 0;
 190                 case HDLC_FAST_IDLE:
 191                         if (hdlc->cbin == 0xff) {
 192                                 hdlc->bit_shift = 0;
 193                                 break;
 194                         }
 195                         hdlc->state = HDLC_GET_FLAG_B0;
 196                         hdlc->hdlc_bits1 = 0;
 197                         hdlc->bit_shift = 8;
 198                         break;
 199                 case HDLC_GET_FLAG_B0:
 200                         if (!(hdlc->cbin & 0x80)) {
 201                                 hdlc->state = HDLC_GETFLAG_B1A6;
 202                                 hdlc->hdlc_bits1 = 0;
 203                         } else {
 204                                 if ((!hdlc->do_adapt56) &&
 205                                     (++hdlc->hdlc_bits1 >= 8) &&
 206                                     (hdlc->bit_shift == 1))
 207                                                 hdlc->state = HDLC_FAST_IDLE;
 208                         }
 209                         hdlc->cbin <<= 1;
 210                         hdlc->bit_shift--;
 211                         break;
 212                 case HDLC_GETFLAG_B1A6:
 213                         if (hdlc->cbin & 0x80) {
 214                                 hdlc->hdlc_bits1++;
 215                                 if (hdlc->hdlc_bits1 == 6)
 216                                         hdlc->state = HDLC_GETFLAG_B7;
 217                         } else
 218                                 hdlc->hdlc_bits1 = 0;
 219                         hdlc->cbin <<= 1;
 220                         hdlc->bit_shift--;
 221                         break;
 222                 case HDLC_GETFLAG_B7:
 223                         if (hdlc->cbin & 0x80) {
 224                                 hdlc->state = HDLC_GET_FLAG_B0;
 225                         } else {
 226                                 hdlc->state = HDLC_GET_DATA;
 227                                 hdlc->crc = 0xffff;
 228                                 hdlc->shift_reg = 0;
 229                                 hdlc->hdlc_bits1 = 0;
 230                                 hdlc->data_bits = 0;
 231                                 hdlc->data_received = 0;
 232                         }
 233                         hdlc->cbin <<= 1;
 234                         hdlc->bit_shift--;
 235                         break;
 236                 case HDLC_GET_DATA:
 237                         if (hdlc->cbin & 0x80) {
 238                                 hdlc->hdlc_bits1++;
 239                                 switch (hdlc->hdlc_bits1) {
 240                                 case 6:
 241                                         break;
 242                                 case 7:
 243                                         if (hdlc->data_received)
 244                                                 /* bad frame */
 245                                                 status = -HDLC_FRAMING_ERROR;
 246                                         if (!hdlc->do_adapt56) {
 247                                                 if (hdlc->cbin == fast_abort
 248                                                     [hdlc->bit_shift + 1]) {
 249                                                         hdlc->state =
 250                                                                 HDLC_FAST_IDLE;
 251                                                         hdlc->bit_shift = 1;
 252                                                         break;
 253                                                 }
 254                                         } else
 255                                                 hdlc->state = HDLC_GET_FLAG_B0;
 256                                         break;
 257                                 default:
 258                                         hdlc->shift_reg >>= 1;
 259                                         hdlc->shift_reg |= 0x80;
 260                                         hdlc->data_bits++;
 261                                         break;
 262                                 }
 263                         } else {
 264                                 switch (hdlc->hdlc_bits1) {
 265                                 case 5:
 266                                         break;
 267                                 case 6:
 268                                         if (hdlc->data_received)
 269                                                 status = check_frame(hdlc);
 270                                         hdlc->crc = 0xffff;
 271                                         hdlc->shift_reg = 0;
 272                                         hdlc->data_bits = 0;
 273                                         if (!hdlc->do_adapt56)
 274                                                 handle_fast_flag(hdlc);
 275                                         else {
 276                                                 hdlc->state = HDLC_GET_DATA;
 277                                                 hdlc->data_received = 0;
 278                                         }
 279                                         break;
 280                                 default:
 281                                         hdlc->shift_reg >>= 1;
 282                                         hdlc->data_bits++;
 283                                         break;
 284                                 }
 285                                 hdlc->hdlc_bits1 = 0;
 286                         }
 287                         if (status) {
 288                                 hdlc->dstpos = 0;
 289                                 *count -= slen;
 290                                 hdlc->cbin <<= 1;
 291                                 hdlc->bit_shift--;
 292                                 return status;
 293                         }
 294                         if (hdlc->data_bits == 8) {
 295                                 hdlc->data_bits = 0;
 296                                 hdlc->data_received = 1;
 297                                 hdlc->crc = crc_ccitt_byte(hdlc->crc,
 298                                                 hdlc->shift_reg);
 299
 300                                 /* good byte received */
 301                                 if (hdlc->dstpos < dsize)
 302                                         dst[hdlc->dstpos++] = hdlc->shift_reg;
 303                                 else {
 304                                         /* frame too long */
 305                                         status = -HDLC_LENGTH_ERROR;
 306                                         hdlc->dstpos = 0;
 307                                 }
 308                         }
 309                         hdlc->cbin <<= 1;
 310                         hdlc->bit_shift--;
 311                         break;
 312                 case HDLC_FAST_FLAG:
 313                         if (hdlc->cbin == hdlc->ffvalue) {
 314                                 hdlc->bit_shift = 0;
 315                                 break;
 316                         } else {
 317                                 if (hdlc->cbin == 0xff) {
 318                                         hdlc->state = HDLC_FAST_IDLE;
 319                                         hdlc->bit_shift = 0;
 320                                 } else if (hdlc->ffbit_shift == 8) {
 321                                         hdlc->state = HDLC_GETFLAG_B7;
 322                                         break;
 323                                 } else
 324                                         handle_abort(hdlc);
 325                         }
 326                         break;
 327                 default:
 328                         break;
 329                 }
 330         }
 331         *count -= slen;
 332         return 0;
 333 }
 334 EXPORT_SYMBOL(isdnhdlc_decode);
 335 /*
 336   isdnhdlc_encode - encodes HDLC frames to a transparent bit stream.
 337
 338   The bit stream starts with a beginning flag (01111110). After
 339   that each byte is added to the bit stream with bit stuffing added
 340   (0 after 5 1's).
 341   When the last byte has been removed from the source buffer, the
 342   CRC (2 bytes is added) and the frame terminates with the ending flag.
 343   For the dchannel, the idle character (all 1's) is also added at the end.
 344   If this function is called with empty source buffer (slen=0), flags or
 345   idle character will be generated.
 346
 347   src - source buffer
 348   slen - source buffer length
 349   count - number of bytes removed (encoded) from source buffer
 350   dst _ destination buffer
 351   dsize - destination buffer size
 352   returns - number of encoded bytes in the destination buffer
 353 */
 354 int isdnhdlc_encode(struct isdnhdlc_vars *hdlc, const u8 *src, u16 slen,
 355         int *count, u8 *dst, int dsize)
 356 {
 357         static const unsigned char xfast_flag_value[] = {
 358                 0x7e, 0x3f, 0x9f, 0xcf, 0xe7, 0xf3, 0xf9, 0xfc, 0x7e
 359         };
 360
 361         int len = 0;
 362
 363         *count = slen;
 364
 365         /* special handling for one byte frames */
 366         if ((slen == 1) && (hdlc->state == HDLC_SEND_FAST_FLAG))
 367                 hdlc->state = HDLC_SENDFLAG_ONE;
 368         while (dsize > 0) {
 369                 if (hdlc->bit_shift == 0) {
 370                         if (slen && !hdlc->do_closing) {
 371                                 hdlc->shift_reg = *src++;
 372                                 slen--;
 373                                 if (slen == 0)
 374                                         /* closing sequence, CRC + flag(s) */
 375                                         hdlc->do_closing = 1;
 376                                 hdlc->bit_shift = 8;
 377                         } else {
 378                                 if (hdlc->state == HDLC_SEND_DATA) {
 379                                         if (hdlc->data_received) {
 380                                                 hdlc->state = HDLC_SEND_CRC1;
 381                                                 hdlc->crc ^= 0xffff;
 382                                                 hdlc->bit_shift = 8;
 383                                                 hdlc->shift_reg =
 384                                                         hdlc->crc & 0xff;
 385                                         } else if (!hdlc->do_adapt56)
 386                                                 hdlc->state =
 387                                                         HDLC_SEND_FAST_FLAG;
 388                                         else
 389                                                 hdlc->state =
 390                                                         HDLC_SENDFLAG_B0;
 391                                 }
 392
 393                         }
 394                 }
 395
 396                 switch (hdlc->state) {
 397                 case STOPPED:
 398                         while (dsize--)
 399                                 *dst++ = 0xff;
 400                         return dsize;
 401                 case HDLC_SEND_FAST_FLAG:
 402                         hdlc->do_closing = 0;
 403                         if (slen == 0) {
 404                                 /* the code is for bitreverse streams */
 405                                 if (hdlc->do_bitreverse == 0)
 406                                         *dst++ = bitrev8(hdlc->ffvalue);
 407                                 else
 408                                         *dst++ = hdlc->ffvalue;
 409                                 len++;
 410                                 dsize--;
 411                                 break;
 412                         }
 413                         /* fall through */
 414                 case HDLC_SENDFLAG_ONE:
 415                         if (hdlc->bit_shift == 8) {
 416                                 hdlc->cbin = hdlc->ffvalue >>
 417                                         (8 - hdlc->data_bits);
 418                                 hdlc->state = HDLC_SEND_DATA;
 419                                 hdlc->crc = 0xffff;
 420                                 hdlc->hdlc_bits1 = 0;
 421                                 hdlc->data_received = 1;
 422                         }
 423                         break;
 424                 case HDLC_SENDFLAG_B0:
 425                         hdlc->do_closing = 0;
 426                         hdlc->cbin <<= 1;
 427                         hdlc->data_bits++;
 428                         hdlc->hdlc_bits1 = 0;
 429                         hdlc->state = HDLC_SENDFLAG_B1A6;
 430                         break;
 431                 case HDLC_SENDFLAG_B1A6:
 432                         hdlc->cbin <<= 1;
 433                         hdlc->data_bits++;
 434                         hdlc->cbin++;
 435                         if (++hdlc->hdlc_bits1 == 6)
 436                                 hdlc->state = HDLC_SENDFLAG_B7;
 437                         break;
 438                 case HDLC_SENDFLAG_B7:
 439                         hdlc->cbin <<= 1;
 440                         hdlc->data_bits++;
 441                         if (slen == 0) {
 442                                 hdlc->state = HDLC_SENDFLAG_B0;
 443                                 break;
 444                         }
 445                         if (hdlc->bit_shift == 8) {
 446                                 hdlc->state = HDLC_SEND_DATA;
 447                                 hdlc->crc = 0xffff;
 448                                 hdlc->hdlc_bits1 = 0;
 449                                 hdlc->data_received = 1;
 450                         }
 451                         break;
 452                 case HDLC_SEND_FIRST_FLAG:
 453                         hdlc->data_received = 1;
 454                         if (hdlc->data_bits == 8) {
 455                                 hdlc->state = HDLC_SEND_DATA;
 456                                 hdlc->crc = 0xffff;
 457                                 hdlc->hdlc_bits1 = 0;
 458                                 break;
 459                         }
 460                         hdlc->cbin <<= 1;
 461                         hdlc->data_bits++;
 462                         if (hdlc->shift_reg & 0x01)
 463                                 hdlc->cbin++;
 464                         hdlc->shift_reg >>= 1;
 465                         hdlc->bit_shift--;
 466                         if (hdlc->bit_shift == 0) {
 467                                 hdlc->state = HDLC_SEND_DATA;
 468                                 hdlc->crc = 0xffff;
 469                                 hdlc->hdlc_bits1 = 0;
 470                         }
 471                         break;
 472                 case HDLC_SEND_DATA:
 473                         hdlc->cbin <<= 1;
 474                         hdlc->data_bits++;
 475                         if (hdlc->hdlc_bits1 == 5) {
 476                                 hdlc->hdlc_bits1 = 0;
 477                                 break;
 478                         }
 479                         if (hdlc->bit_shift == 8)
 480                                 hdlc->crc = crc_ccitt_byte(hdlc->crc,
 481                                         hdlc->shift_reg);
 482                         if (hdlc->shift_reg & 0x01) {
 483                                 hdlc->hdlc_bits1++;
 484                                 hdlc->cbin++;
 485                                 hdlc->shift_reg >>= 1;
 486                                 hdlc->bit_shift--;
 487                         } else {
 488                                 hdlc->hdlc_bits1 = 0;
 489                                 hdlc->shift_reg >>= 1;
 490                                 hdlc->bit_shift--;
 491                         }
 492                         break;
 493                 case HDLC_SEND_CRC1:
 494                         hdlc->cbin <<= 1;
 495                         hdlc->data_bits++;
 496                         if (hdlc->hdlc_bits1 == 5) {
 497                                 hdlc->hdlc_bits1 = 0;
 498                                 break;
 499                         }
 500                         if (hdlc->shift_reg & 0x01) {
 501                                 hdlc->hdlc_bits1++;
 502                                 hdlc->cbin++;
 503                                 hdlc->shift_reg >>= 1;
 504                                 hdlc->bit_shift--;
 505                         } else {
 506                                 hdlc->hdlc_bits1 = 0;
 507                                 hdlc->shift_reg >>= 1;
 508                                 hdlc->bit_shift--;
 509                         }
 510                         if (hdlc->bit_shift == 0) {
 511                                 hdlc->shift_reg = (hdlc->crc >> 8);
 512                                 hdlc->state = HDLC_SEND_CRC2;
 513                                 hdlc->bit_shift = 8;
 514                         }
 515                         break;
 516                 case HDLC_SEND_CRC2:
 517                         hdlc->cbin <<= 1;
 518                         hdlc->data_bits++;
 519                         if (hdlc->hdlc_bits1 == 5) {
 520                                 hdlc->hdlc_bits1 = 0;
 521                                 break;
 522                         }
 523                         if (hdlc->shift_reg & 0x01) {
 524                                 hdlc->hdlc_bits1++;
 525                                 hdlc->cbin++;
 526                                 hdlc->shift_reg >>= 1;
 527                                 hdlc->bit_shift--;
 528                         } else {
 529                                 hdlc->hdlc_bits1 = 0;
 530                                 hdlc->shift_reg >>= 1;
 531                                 hdlc->bit_shift--;
 532                         }
 533                         if (hdlc->bit_shift == 0) {
 534                                 hdlc->shift_reg = 0x7e;
 535                                 hdlc->state = HDLC_SEND_CLOSING_FLAG;
 536                                 hdlc->bit_shift = 8;
 537                         }
 538                         break;
 539                 case HDLC_SEND_CLOSING_FLAG:
 540                         hdlc->cbin <<= 1;
 541                         hdlc->data_bits++;
 542                         if (hdlc->hdlc_bits1 == 5) {
 543                                 hdlc->hdlc_bits1 = 0;
 544                                 break;
 545                         }
 546                         if (hdlc->shift_reg & 0x01)
 547                                 hdlc->cbin++;
 548                         hdlc->shift_reg >>= 1;
 549                         hdlc->bit_shift--;
 550                         if (hdlc->bit_shift == 0) {
 551                                 hdlc->ffvalue =
 552                                         xfast_flag_value[hdlc->data_bits];
 553                                 if (hdlc->dchannel) {
 554                                         hdlc->ffvalue = 0x7e;
 555                                         hdlc->state = HDLC_SEND_IDLE1;
 556                                         hdlc->bit_shift = 8-hdlc->data_bits;
 557                                         if (hdlc->bit_shift == 0)
 558                                                 hdlc->state =
 559                                                         HDLC_SEND_FAST_IDLE;
 560                                 } else {
 561                                         if (!hdlc->do_adapt56) {
 562                                                 hdlc->state =
 563                                                         HDLC_SEND_FAST_FLAG;
 564                                                 hdlc->data_received = 0;
 565                                         } else {
 566                                                 hdlc->state = HDLC_SENDFLAG_B0;
 567                                                 hdlc->data_received = 0;
 568                                         }
 569                                         /* Finished this frame, send flags */
 570                                         if (dsize > 1)
 571                                                 dsize = 1;
 572                                 }
 573                         }
 574                         break;
 575                 case HDLC_SEND_IDLE1:
 576                         hdlc->do_closing = 0;
 577                         hdlc->cbin <<= 1;
 578                         hdlc->cbin++;
 579                         hdlc->data_bits++;
 580                         hdlc->bit_shift--;
 581                         if (hdlc->bit_shift == 0) {
 582                                 hdlc->state = HDLC_SEND_FAST_IDLE;
 583                                 hdlc->bit_shift = 0;
 584                         }
 585                         break;
 586                 case HDLC_SEND_FAST_IDLE:
 587                         hdlc->do_closing = 0;
 588                         hdlc->cbin = 0xff;
 589                         hdlc->data_bits = 8;
 590                         if (hdlc->bit_shift == 8) {
 591                                 hdlc->cbin = 0x7e;
 592                                 hdlc->state = HDLC_SEND_FIRST_FLAG;
 593                         } else {
 594                                 /* the code is for bitreverse streams */
 595                                 if (hdlc->do_bitreverse == 0)
 596                                         *dst++ = bitrev8(hdlc->cbin);
 597                                 else
 598                                         *dst++ = hdlc->cbin;
 599                                 hdlc->bit_shift = 0;
 600                                 hdlc->data_bits = 0;
 601                                 len++;
 602                                 dsize = 0;
 603                         }
 604                         break;
 605                 default:
 606                         break;
 607                 }
 608                 if (hdlc->do_adapt56) {
 609                         if (hdlc->data_bits == 7) {
 610                                 hdlc->cbin <<= 1;
 611                                 hdlc->cbin++;
 612                                 hdlc->data_bits++;
 613                         }
 614                 }
 615                 if (hdlc->data_bits == 8) {
 616                         /* the code is for bitreverse streams */
 617                         if (hdlc->do_bitreverse == 0)
 618                                 *dst++ = bitrev8(hdlc->cbin);
 619                         else
 620                                 *dst++ = hdlc->cbin;
 621                         hdlc->data_bits = 0;
 622                         len++;
 623                         dsize--;
 624                 }
 625         }
 626         *count -= slen;
 627
 628         return len;
 629 }
 630 EXPORT_SYMBOL(isdnhdlc_encode);