That is to say that when the CRC checker in the module performs the check on the data blocks received, the final "total" CRC value is 0xFFFF. It should be 0x0000.

Note that this error only occures when my CRC generator is run on a block-by-block basis, rather than the whole file all at once:

   @data = read_data($infile);            # @data is global
   $data[0x6FFE] = 0;                     # zero CRC
   $data[0x6FFF = 0;                      # locations

   $crc = crc16(0x0000, 0x6FFF,  0);          # works

   $crc = 0;
   for ($a = 0x0000; $a < 0x6fff; $a += 32) { # final value
      next if (unusedBlock($a, 32);           # off by one
      $crc = crc16($a,     $a + 32, $crc);
   }


   $data[0x6FFE] = $crc >> 8;                 # save
   $data[0x6FFF] = $crc & 0xFF;               # CRC
   write_data($outfile); # or write_data_blocks($outfile);
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Obviously, the block-by-block CRC is based on fewer bytes than the full CRC, so is, as expected, different.

The module software is designed handle the data download in blocks, and, therefore, runs it CRC calculation block-by-block. In fact, even when the whole file is downloaded, it is still blocked. The difference is that all blocks are sent for the whole file, while only a subset for block-by-block.

Below are my Perl CRC routine (called by the above code) and the C source of the module's CRC routine.

sub crc16 ($$$)
{
   my ($startadr, $endadr, $crc) = @_;
   my ($cadr, $adr, $i, $u, $d);

   for ($adr = $startadr; $adr <= $endadr; $adr++) {
      if (defined($data[$adr])) {
         $d = $data[$adr] & 0xFF;
      } else {
         $d = 0xFF;
      }
      $i = $crc >> 8;
      $crc <<= 8;
      $crc &= 0xFFFF;
      $crc |= $d;
      $crc ^= $crctable[$i];
   }
   return $crc;
}
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void VerifyFlashBlock(UINT8  len, UINT16 address)
{
   UINT8 byte_value;
   UINT8 crc_table_index;

   for (;len > 0; len--) {
      byte_value = _READ_BYTE_FROM_FLASH(address);
      crc_table_index = crc >> 8;
      crc = (crc << 8) | byte_value;
      crc = crc ^ _Crc_table[crc_table_index];

      address++;
      buffer++;
   }
}
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