Functional Decriptions
PRELIMINARY DRAFT
always start on an ECC boundary. The HW monitors the subsequent ID to detect any
interruption in the DVD data stream.
After sufficient data is stored (at least 1 ECC Block = 16 sectors) in the Buffer, the Error
Correction (ECC) system can start the Error Detection and Correction. The Error
Correction algorithm is programmable to allow for multi-pass correction, depending
upon the application e.g. in the DVD-ROM case, one would program it with more passes
than for DVD-Movie case.
Once ECC system has corrected one ECC block, this data can be transferred to the
host. However before transferring this data need to be de-scrambled. The de-
scrambling process is done during Host transfer to save Buffer BW.
All the Disc Transfer, ECC correction, Descrambling and Host Transfers are done in
parallel without any intervention from the micro-controller. The hardware keeps track of
how many sectors are transferred from the disc to the buffer, how many sectors have
been corrected and how many transferred to the host. This is a fully automated
operation also known as "full streaming".
CD Form
The actual data that is written on the CD DISC is a transformed version of the user data
and follows the CD Physical Specification. The Physical format of a CD disc is defined
by the CD-Digital Audio Physical Specification. All CD whether CD-ROM or CD-Audio
follows this standard. The recordable formats also follow this format, except for the
linking area for multi-session recordings.
Again it is beyond the scope of this document to describe the CD formats as unlike the
DVD format, there are host of different formats that the decoder needs to process.
These are CD-DA, CD-ROM Mode 0, CD-ROM Mode 2/Form1 CD-ROM Mode 2/ Form
2 plus CD-Recordable data. In addition for the CD-DA mode the decoder needs to
process the Sub Channel Data. The Sub-Channel contains additional information that is
embedded in the EFM data stream, which contains sector identifications and other
information unique to the data.
Basically there are two types of data, CD-Audio and CD-ROM (with different modes and
form). For CD-Audio both the main channel and the Sub Channel Data needs to be
processed, for the CD-ROM case only the main channel data is processed.
The data arriving from the Read Channel is in the EFM format, first it is synchronized
and aligned on the EFM frame boundaries. After synchronization the data is
demodulated using the EFM demodulation table.
CD data is protected through 2 levels of correction C1 and C2 for the CD-DA and 3
levels C1, C2 and C3 for CD-ROM formats.
C1 and C2 correction is done on the fly, i.e. before the data is transferred to the Buffer.
After EFM demodulation, the data is sent to CIRC block (Cross Interleaved Reed
Solomon Code) which performs C1 and C2 correction on the incoming data. It also
marks data it cannot correct, these markers called C2 Pointers are used by the Audio
Interpolator block to perform audio interpolation and in the case of CD-ROM data, help
the C3 correction engine in identifying the errors quickly.
After the EFM demodulation, the Target Header Search looks for the target sector ID in
the data stream. In the case of CD-DA this ID is in the sub channel data stream,
CONFIDEN TIAL
DS588PP1 - rev 0.4 April 11, 2002
Copyright 2002 Cirrus Logic Inc.
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