drivers/isdn/tpam/tpam_crcpc.c

   1 /* $Id: tpam_crcpc.c,v 1.1.2.2 2001/09/23 22:25:03 kai Exp $
   2  *
   3  * Turbo PAM ISDN driver for Linux. (Kernel Driver - CRC encoding)
   4  *
   5  * Copyright 1998-2000 AUVERTECH Télécom
   6  * Copyright 2001 Stelian Pop <stelian.pop@fr.alcove.com>, Alcôve
   7  *
   8  * This software may be used and distributed according to the terms
   9  * of the GNU General Public License, incorporated herein by reference.
  10  *
  11  * For all support questions please contact: <support@auvertech.fr>
  12  *
  13  */
  14
  15 /*+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  16
  17 Module Name:
  18
  19     crcpc.c
  20
  21 Abstract:
  22
  23     Modem HDLC coding
  24     Software HDLC coding / decoding
  25
  26 Revision History:
  27
  28 ---------------------------------------------------------------------------*/
  29
  30 #include <linux/crc-ccitt.h>
  31 #include "tpam.h"
  32
  33 #define  HDLC_CTRL_CHAR_CMPL_MASK       0x20    /* HDLC control character complement mask */
  34 #define  HDLC_FLAG                      0x7E    /* HDLC flag */
  35 #define  HDLC_CTRL_ESC                  0x7D    /* HDLC control escapr character */
  36 #define  HDLC_LIKE_FCS_INIT_VAL         0xFFFF  /* FCS initial value (0xFFFF for new equipment or 0) */
  37 #define  HDLC_FCS_OK                    0xF0B8  /* This value is the only valid value of FCS */
  38
  39 #define TRUE    1
  40 #define FALSE   0
  41
  42 static u8 ap_t_ctrl_char_complemented[256]; /* list of characters to complement */
  43
  44 static void ap_hdlc_like_ctrl_char_list (u32 ctrl_char) {
  45         int i;
  46
  47         for (i = 0; i < 256; ++i)
  48                 ap_t_ctrl_char_complemented[i] = FALSE;
  49         for (i = 0; i < 32; ++i)
  50                 if ((ctrl_char >> i) & 0x0001)
  51                         ap_t_ctrl_char_complemented [i] = TRUE;
  52         ap_t_ctrl_char_complemented[HDLC_FLAG] = TRUE;
  53         ap_t_ctrl_char_complemented[HDLC_CTRL_ESC] = TRUE;
  54
  55 }
  56
  57 void init_CRC(void) {
  58         ap_hdlc_like_ctrl_char_list(0xffffffff);
  59 }
  60
  61 void hdlc_encode_modem(u8 *buffer_in, u32 lng_in,
  62                        u8 *buffer_out, u32 *lng_out) {
  63         u16 fcs;
  64         register u8 data;
  65         register u8 *p_data_out = buffer_out;
  66
  67         fcs = HDLC_LIKE_FCS_INIT_VAL;
  68
  69         /*
  70          *   Insert HDLC flag at the beginning of the frame
  71          */
  72         *p_data_out++ = HDLC_FLAG;
  73
  74 #define ESCAPE_CHAR(data_out, data) \
  75         if (ap_t_ctrl_char_complemented[data]) { \
  76                 *data_out++ = HDLC_CTRL_ESC; \
  77                 *data_out++ = data ^ 0x20; \
  78         } \
  79         else \
  80                 *data_out++ = data;
  81
  82         while (lng_in--) {
  83                 data = *buffer_in++;
  84
  85                 /*
  86                  *   FCS calculation
  87                  */
  88                 fcs = crc_ccitt_byte(fcs, data);
  89
  90                 ESCAPE_CHAR(p_data_out, data);
  91         }
  92
  93         /*
  94          *  Add FCS and closing flag
  95          */
  96         fcs ^= 0xFFFF;  // Complement
  97
  98         data = (u8)(fcs & 0xff);        /* LSB */
  99         ESCAPE_CHAR(p_data_out, data);
 100
 101         data = (u8)((fcs >> 8));        /* MSB */
 102         ESCAPE_CHAR(p_data_out, data);
 103 #undef ESCAPE_CHAR
 104
 105         *p_data_out++ = HDLC_FLAG;
 106
 107         *lng_out = (u32)(p_data_out - buffer_out);
 108 }
 109
 110 void hdlc_no_accm_encode(u8 *buffer_in, u32 lng_in,
 111                          u8 *buffer_out, u32 *lng_out) {
 112         u16 fcs;
 113         register u8 data;
 114         register u8 *p_data_out = buffer_out;
 115
 116         /*
 117          *   Insert HDLC flag at the beginning of the frame
 118          */
 119         fcs = HDLC_LIKE_FCS_INIT_VAL;
 120
 121         while (lng_in--) {
 122                 data = *buffer_in++;
 123                 /* calculate FCS */
 124                 fcs = crc_ccitt_byte(fcs, data);
 125                 *p_data_out++ = data;
 126         }
 127
 128         /*
 129          *  Add FCS and closing flag
 130          */
 131         fcs ^= 0xFFFF;  // Complement
 132         data = (u8)(fcs);
 133         *p_data_out++ = data;
 134
 135         data =(u8)((fcs >> 8));   // revense MSB / LSB
 136         *p_data_out++ = data;
 137
 138         *lng_out = (u32)(p_data_out - buffer_out);
 139 }
 140
 141 u32 hdlc_no_accm_decode(u8 *buffer_in, u32 lng_in) {
 142         u16 fcs;
 143         u32 lng = lng_in;
 144         register u8 data;
 145
 146         /*
 147          *   Insert HDLC flag at the beginning of the frame
 148          */
 149         fcs = HDLC_LIKE_FCS_INIT_VAL;
 150
 151         while (lng_in--) {
 152                 data = *buffer_in++;
 153                 /* calculate FCS */
 154                 fcs = crc_ccitt_byte(fcs, data);
 155         }
 156
 157         if (fcs == HDLC_FCS_OK)
 158                 return (lng-2);
 159         else
 160                 return 0;
 161 }
 162