SAA7381 Просмотр технического описания (PDF) - Philips Electronics

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SAA7381

ATAPI CD-R block decoder

Philips Electronics 

Philips Semiconductors

ATAPI CD-R block decoder

Objective specification

SAA7381

DATA

Number of C2 flags in

sector (compressed

format)

96-byte de-interleaved

R-W data field

12-byte Q-subcode field

2 copies of STAT4 field

DESCRIPTION

While storage of C2 flag positions is not possible as a consequence of the architecture of

the SAA7381, a count of the number of flags seen per block is made in a single-byte

counter. This counter packs the possibly 12-bit count into a single byte in the following

way, at the expense of resolution in the count values for large counts.

C2count_val = count (5 down to 0) × [4 ^ count (7 down to 6)], the resolution of the count

is therefore:

C2count_val 0 to 63: counter resolution = 1

C2count_val 64 to 255: counter resolution = 4

C2count_val 256 to 1023: counter resolution = 16

C2count_val 1024 to 4095: counter resolution = 64

Written to memory by the automatic Q-channel copy process (copy2 channel). If the copy

process is not enabled, these fields are not written (see Section 7.3.5). These bytes may

either be R-W de-interleaved or presented as raw Q-W subcode bytes. If the copy2

interleaving mode is set to raw, interleaved copying is still required as the subcode

temporary holding buffer has Q bytes interspersed with the raw R-W.

As above: these will not be separated out if the copy2 interleaving option is set to raw.

Address 2465 and 2466 are copies of the STAT4 register written by the ERCO when

enabled. This allows the user to determine if the STAT4 register has been written to by the

ERCO. If seg2465 = seg2466 then STAT4 definitely has not been written by the ERCO.

If seg2465 ≠ seg2466 then STAT4 probably has not been written by the ERCO.

Via direct access to buffer memory, the sub-CPU will be able to look at all of the blocks so

far corrected, to check their status, in a background task.

ERCO failures do not have to be dealt with immediately, as the status of every block

loaded in to RAM is stored with that block, and it is not overwritten until the RAM block is

filled with new data from CD input.

The error corrector will be controlled additionally to permit the use of single pass P-Q or

only EDC operation to allow for greater than n = 14 operation of the ERCO.

The ERCO status will be copied into the RAM along with the data. This is possible

because the RAM now has spare capacity to store the information, as part of the change

from linear to segment/offset addressing.

It is possible to program transfers into RAM of more than one block without processor

intervention. It is also possible to continually loop on the same buffer area of RAM, by not

altering the reload register values when the reload interrupt occurs.

7.1.1 DVD-ROM MEMORY FIELD INFORMATION

The buffer arrangement for DVD usage is basically the same (data followed by flags) but the size of the block data differs,

and the ERCO flags are at a different offset, and as the ERCO is not in use, the flags relating to ERCO performance will

not be valid.

1997 Aug 12

17

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