1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/gdrom/README.LIBEDC	Thu May 29 11:00:26 2008 +0000
     1.3 @@ -0,0 +1,123 @@
     1.4 +This describes the program as shipped with cdrkit, a spinoff from the
     1.5 +cdrtools project. However, the cdrtools developers are no longer 
     1.6 +involved in the development of this spinoff and therefore shall not
     1.7 +be made responsible for any problem caused by it. Do not try to get 
     1.8 +support for this program by contacting the original authors.
     1.9 +
    1.10 +This is a small description for the Reed-Solomon library intended for
    1.11 +CD sector formatting.
    1.12 +
    1.13 +Basics:
    1.14 +It is assumed that you have a basic knowledge of cd sector formats.
    1.15 +
    1.16 +The library can handle three types of sector data:
    1.17 +  data sectors,
    1.18 +  audio sectors, and
    1.19 +  sub channel r-w sectors
    1.20 +
    1.21 +Currently only encoding is implemented. Decoding and optionally
    1.22 +error correction is planned for later.
    1.23 +
    1.24 +Stages:
    1.25 +
    1.26 +The process of sector formatting has several stages. Beginning with
    1.27 +a data sector (2048, 2324, or 2336 bytes) a sector of 2352 bytes is
    1.28 +built. This format can be read raw by SCSI MMC-2 and ATAPI drives and
    1.29 +is accepted by cd burners. The additions are an optionally 32 bit CRC
    1.30 +checksum and two layers of Reed-Solomon codes (called Reed-Solomon
    1.31 +Product Code RSPC).
    1.32 +This sector is then scrambled (exor'ed with a bitstream).
    1.33 +The result is called F1 frames. Afterwards even and odd bytes are
    1.34 +swapped, this is called F2 frames. The result is equivalent to an
    1.35 +audio sector and is treated as such by the cd burner.
    1.36 +So, if we wrote a series of sectors (F2 frames) into a CDR file and
    1.37 +later burned them as 'audio', they would turn up as perfect data sectors.
    1.38 +
    1.39 +So, now we are at the level of audio sectors. Audio sectors get their
    1.40 +own error correction data (called CIRC). Sector size goes up to 
    1.41 +3136 bytes (that is 4/3 times 2352 bytes). Furthermore different
    1.42 +words get delayed differently and swap positions. The result is ready
    1.43 +to be fed into the so-called EightFourteenModulator (when subchannels
    1.44 +have been added).
    1.45 +
    1.46 +Now, only sub channels are missing. While the p and q sub
    1.47 +channels have to be generated elsewhere, any supplied r-w subchannel
    1.48 +user data is protected by two levels of error correction
    1.49 +codes. This format is read by cd burners when burning cd+graphics.
    1.50 +The cdimage is a sequence of sectors, each containing audio data and
    1.51 +after that subchannel data.
    1.52 +Similar to audio sectors delaying and permutation of words
    1.53 +takes place. After that the cd burner would mix sub channel data with
    1.54 +the formatted audio sectors to feed the EFModulator.
    1.55 +
    1.56 +NOTE: Most of the described stages need not to be done in order to
    1.57 +prepare sectors for burning, since all cd burners do at least CIRC,
    1.58 +delaying and swaps. For data sectors they also do scrambling and f2
    1.59 +frame generation.
    1.60 +
    1.61 +Encoding routines:
    1.62 +
    1.63 +For data sectors
    1.64 + int do_encode_L2(unsigned char *inout, int sectortype, unsigned address);
    1.65 +
    1.66 + encodes data sectors. The returned data is __unscrambled__ and not in
    1.67 + F2-frame format.
    1.68 +
    1.69 +Parameters are:
    1.70 +  inout        pointer to an array of at least 2352 bytes.
    1.71 +  sectortype   One of the MODE_* constants from ecc.h. This defines
    1.72 +               how to format the sector.
    1.73 +  address      The logical address to be used in the header 
    1.74 +               (150 = 0:2.0 MSF).
    1.75 +
    1.76 +NOTE: the data portion has be to aligned properly for performance
    1.77 +reasons (see ecc.h for details). So, no moves are necessary here.
    1.78 +
    1.79 +Generating f2 frames to be used like audio sectors
    1.80 + int scramble_L2(unsigned char *inout)
    1.81 +
    1.82 + generates f2 frames in place from sectors generated by do_encode_L2().
    1.83 +
    1.84 +Parameters are:
    1.85 +  inout        pointer to an array of at least 2352 bytes.
    1.86 +
    1.87 +
    1.88 +
    1.89 +For sub channels
    1.90 + int do_encode_sub(unsigned char in[LSUB_RAW*PACKETS_PER_SUBCHANNELFRAME],
    1.91 +		unsigned char out[(LSUB_RAW+LSUB_Q+LSUB_P)*
    1.92 +					PACKETS_PER_SUBCHANNELFRAME],
    1.93 +		int delay1, int permute);
    1.94 +
    1.95 + repack user data and add error correction data. P and q subchannels
    1.96 +should be added later, since all bytes are in place then.
    1.97 +
    1.98 +Parameters are:
    1.99 +  in           pointer to an array of at least 72 bytes. It contains
   1.100 +               the user data for one frame.
   1.101 +  out          pointer to an array of at least 96 bytes. Here is
   1.102 +               output frame is placed.
   1.103 +  delay1       do low level delaying, when set to 1.
   1.104 +  permute      do low level permutations, when set to 1.
   1.105 +
   1.106 +NOTE: Probably both options need either to be set on (1) or off (0) together.
   1.107 +
   1.108 +There is more, but that is seldomly used.
   1.109 +
   1.110 +Tests:
   1.111 +The library is accompanied by small verify programs, that compare real
   1.112 +raw sectors with the formatted results. They are also intended as demo
   1.113 +applications (how to use the library). In order to be able to feed
   1.114 +real raw sectors into them, the package read2448 is recommended/needed.
   1.115 +You can only verify sector streams of one sector type, currently no mix.
   1.116 +
   1.117 +For more information have a look into ecc.h
   1.118 +
   1.119 +recommended Documents:
   1.120 +Yellow Book or ISO 10149
   1.121 +Appendix Red Book
   1.122 +Red Book or IEC 908
   1.123 +
   1.124 +Source: libedc/README from cdrtools package
   1.125 +Edited for cdrkit by Christian Fromme <kaner@strace.org>
   1.126 +