tools/telechips.c

   1 /***************************************************************************
   2  *             __________               __   ___.
   3  *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
   4  *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
   5  *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
   6  *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
   7  *                     \/            \/     \/    \/            \/
   8  * $Id$
   9  *
  10  * Telechips firmware checksum support for scramble
  11  *
  12  * Copyright (C) 2007 Dave Chapman
  13  *
  14  * Thanks to Hein-Pieter van Braam for his work in identifying the
  15  * CRC algorithm used.
  16  *
  17  * This program is free software; you can redistribute it and/or
  18  * modify it under the terms of the GNU General Public License
  19  * as published by the Free Software Foundation; either version 2
  20  * of the License, or (at your option) any later version.
  21  *
  22  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  23  * KIND, either express or implied.
  24  *
  25  ****************************************************************************/
  26
  27 #include <stdio.h>
  28 #include <unistd.h>
  29 #include <sys/types.h>
  30 #include <sys/stat.h>
  31 #include <fcntl.h>
  32 #include <stdint.h>
  33 #include <stdlib.h>
  34
  35 static uint32_t crctable[256];
  36
  37 /* Simple implementation of a function to reverse the bottom n bits in x */
  38 static uint32_t bitreverse(uint32_t x,int n)
  39 {
  40     int i;
  41     uint32_t mask = 1<<(n-1);
  42     uint32_t res = 0;
  43
  44     for (i=0; i<n; i++)
  45     {
  46         if (x & 1)
  47             res |=  mask;
  48
  49         x >>= 1;
  50         mask >>= 1;
  51     }
  52     return res;
  53 }
  54
  55 /* Generate a lookup table for a reverse CRC32 */
  56 static void gentable(uint32_t poly)
  57 {
  58     int i;
  59     uint32_t r;
  60     uint32_t index;
  61
  62     for (index = 0; index < 256; index++)
  63     {
  64         r = bitreverse(index,8) << 24;
  65         for (i=0; i<8; i++)
  66         {
  67             if (r & (1 << 31))
  68                 r = (r << 1) ^ poly;
  69             else
  70                 r<<=1;
  71         }
  72         crctable[index] = bitreverse(r,32);
  73     }
  74 }
  75
  76 /* Perform a reverse CRC32 */
  77 static uint32_t calc_crc(unsigned char *message, int size)
  78 {
  79     uint32_t crc = 0;
  80     int i;
  81
  82     for (i=0; i < size; i++){
  83         if ((i < 0x10) || (i >= 0x18)) {
  84             crc = crctable[((crc ^ (message[i])) & 0xff)] ^ (crc >> 8);
  85         }
  86     }
  87
  88     return crc;
  89 }
  90
  91 /* Endian-safe functions to read/write a 32-bit little-endian integer */
  92
  93 static uint32_t get_uint32le(unsigned char* p)
  94 {
  95     return p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);
  96 }
  97
  98 static void put_uint32le(unsigned char* p, uint32_t x)
  99 {
 100     p[0] = x & 0xff;
 101     p[1] = (x >> 8) & 0xff;
 102     p[2] = (x >> 16) & 0xff;
 103     p[3] = (x >> 24) & 0xff;
 104 }
 105
 106 /* A simple checksum - seems to be used by the TCC76x firmwares */
 107 void telechips_encode_sum(unsigned char* buf, int length)
 108 {
 109     uint32_t sum;
 110     int i;
 111
 112     /* Set checksum field to 0 */
 113     put_uint32le(buf + 0x10, 0);
 114
 115     /* Perform a simple sum, treating the file as a series of 32-bit
 116        little-endian integers */
 117     sum = 0;
 118     for (i=0; i < length; i+=4) {
 119         sum += get_uint32le(buf + i);
 120     }
 121     /* Negate the sum - this means that the sum of the whole file
 122        (including this value) will be equal to zero */
 123     sum = -sum;
 124
 125     /* Set the checksum field */
 126     put_uint32le(buf + 0x10, sum);
 127 }
 128
 129
 130 /* Two reverse CRC32 checksums - seems to be used by the TCC77x firmwares */
 131 void telechips_encode_crc(unsigned char* buf, int length)
 132 {
 133     uint32_t crc1,crc2;
 134
 135     /* Generate the CRC table */
 136     gentable(0x8001801BL);
 137
 138     /* Clear the existing CRC values */
 139     put_uint32le(buf+0x10, 0);
 140     put_uint32le(buf+0x18, 0);
 141
 142     /* Write the length */
 143     put_uint32le(buf+0x1c, length);
 144
 145     /* Calculate the first CRC - over the entire file */
 146     crc1 = calc_crc(buf, length);
 147
 148     /* What happens next depends on the filesize */
 149     if (length >= 128*1024)
 150     {
 151         put_uint32le(buf+0x18, crc1);
 152
 153         crc2 = calc_crc(buf, 128*1024);
 154         put_uint32le(buf+0x10, crc2);
 155     } else {
 156         put_uint32le(buf+0x10, crc1);
 157     }
 158 }