SH7261 datasheet(1032/1348 Pages) RENESAS

1032 / 1348 page

Section 21 CD-ROM Decoder (ROM-DEC)

Rev. 2.00 Sep. 07, 2007 Page 1000 of 1312

REJ09B0320-0200

21.4.3

Error Correction

The CD-ROM decoder handles data in the formats containing information relevant to error

correction, including the EDC, P parity, and Q parity. The CD-ROM decoder includes the

following features for use in error correction.

• Syndrome calculation

• ECC correction

• EDC checking

(1)

Syndrome Calculation

After the data of a sector in Mode 1 or Form 1 of Mode 2 has been input, the ECC is used in

correction if any error is detected (the result of syndrome calculation is non-zero). After

correction, the results of syndrome operation for the corrected data are output to bits ST_ECCP (P

parity) and ST_ECCQ (Q parity) in the CROMST6 register, respectively.

(2)

ECC correction and EDC Checking

For CD-ROM format data that contains EDC, P-parity, and Q-parity fields, the CD-ROM decoder

performs EDC checking and ECC correction. Supported correction modes are P correction, Q

correction, PQ correction (P correction followed by Q correction), and QP correction (Q

correction followed by P correction). In PQ and QP correction modes, up to three iterations of

correction are possible (the number of iterations is limited by the playback speed).

The EDC check is performed twice, before and after correction.

The mode of ECC correction and EDC checking is specified by bits MD_DEC[2:0] in the

CROMCTL1 register. When the PQ or QP correction mode is selected, the number of iterations is

specified by bits MD_PQREP[1:0] in the CROMCTL1 register.

When the automatic mode/form detection function is in use, the sector mode determines whether

or not ECC correction and EDC checking can be performed. For sectors in Mode 0 and Mode 2

(non-XA), which include neither parity bits nor EDC, ECC correction and EDC checking are not

performed. For sectors in Form 2 of Mode 2, ECC correction is not performed.

(a)

ECC Correction

When ECC correction is in use and an error in a sector is identified as non-correctable, the CD-

ROM decoder generates an IERR interrupt and sets the ST_ECCNG bit of the CROMST6 register

to 1. The CD-ROM detector also sets this bit to 1 on detecting a short sector.

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