Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-11-18
2003-07-15
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06594794
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a read-channel circuitry of data read from a mass memory support such as a DVD or a CD and more in particular to an integrated system for decoding according to the Reed-Solomon algorithm data read from a mass memory support coded according to standard DVD-ROM, DVD-R, DVD-RAM or CD-ROM protocols.
BACKGROUND
DVD and CD optical supports are more and more used for storing large quantities of data in PC's, digital audio and video playback systems and the like. The storing and reading of data to and from these supports imply the coding and decoding of data according to standard protocols that are defined at international level (e.g. ISO/IEC, CEI/IEC, etc.).
In write-read channel circuitry, reliability in terms of ability of detecting and correcting errors, especially during a phase of decoding of the coded data read from the support during a reading phase, and speed are of paramount importance. Obvious cost-effectiveness considerations call for the highest level of integration of system and/or subsystem circuitries in the minimum number of distinct integrated circuits. Multifunctional Reed-Solomon decoders, capable of handling either DVD decoding and correction or CIRC decoding and correction for all the commonly used CD-modes should be advantageously integrated in a single device including-an embedded RAM required for the decoding and correction operations on a bitstream of input data as produced by the data aquisition means of the read channel.
An architectural layout of such a multifunctional decoder ECC-IC is depicted in FIG.
1
.
The integrated decoder handles CD modes bitstreams of any format as well as DVD-ROM, DVD-RAM and DVD-R mode bitstreams and advantageously should possess speed capabilities of handling bitstreams equivalent to a significantly large multiple of standard or base CD rates and of standard or base DVD rates.
With reference to the functional diagram of
FIG. 1
, the multifunctional integrated decoder ECC-IC, when operating in DVD mode, performs horizontal and vertical decoding of the input data stream and the decoded data are then descrambled and EDC checked before sending them to an output interface circuitry. When operating in a CD mode, the data are decoded and deinterleaved without performing any C
3
decoding. Finally, when functioning in a BCA mode, the integrated decoder may perform a Burst Cutting Area decoding of the data stream.
The input data stream consists of the signals output by a data aquisition IC as depicted in FIG.
2
. The signals contain data, information about the data and address information.
byte_clk [
1
]
The byte_clk (byte clock) signal indicates that the data byte can be read. It is generated once per data byte for 1 system clock cycle.
erasure [
1
]
The erasure bit is set to 1 if the current data byte is not a valid 16/8 modulation pattern (14/8 for CD)—if the pattern is valid, erasure is set to 0.
data [
8
]
The 8-bit data bus contains the demodulated data byte.
SID [
4
]
The 4-bit SID (sector ID) contains the 4 least significant bits of the logical sector ID. This signal provides the sector address within each block.
id_error [
1
]
An id_error bit of 0 indicates that the SD was decoded with no errors and no corrections. If the SID contained errors (no correction possible) or if a single error was corrected, the id_error bit is set to 1.
DVD/BCA frame_address[
4
:
0
] or CD S
0
/S
1
In DVD modes the acquisition part keeps a memory of the syncs received and from this history extract the 5-bit frame address.
In BCA mode frame_address[
3
:
0
] depends from the sync found (SB
BCA
, RS
BCA
1
, . . . , RS
BCA
n, RS
BCA
13
, RS
BCA
14
, RS
BCA
15
).
In CD mode the S
0
and S
1
signals are sent on frame_address[
0
] and frame_address[
1
] respectively.
CD nxfr [
1
] or DVD next_frame[
1
]
The DVD next_frame indicates that a new DVD frame is starting. The CD nxfr signal indicates that a new CD frame is starting. The BCA next_frame indicates that a BCA Re-sync has been found.
The timing diagrams of the input data aquisition for the case of operation in DVD mode and in CD mode are shown in
FIGS. 3 and 4
, respectively.
ECC-IC has two kinds of output interface: one for CD-modes (serial) and one for DVD-modes (parallel). In particular, the CD output interface may be a common I
2
S interface employing a format as depicted in
FIG. 5
, and the subcode interface has as format as depicted in FIG.
6
.
The Reed-Solomon decoder block depicted in
FIG. 7
, supports five main modes:
1) DVD Outer code (208, 192, 17)
8 errors or 16 erasures
2) DVD Inner code (182, 172, 11)
5 errors or 10 erasures
3) CD C1 code (32, 28, 5)
2 errors
4) CD C2 code (28, 24, 5)
2 errors or 4 erasures
5) BCA code (52, 48, 5)
2 errors or 4 erasures
The number of erasures that can be corrected is programmable, depending on the mode, from 13 up to 16 for DVD Outer, from 7 up to 10 for DVD Inner, from 1 up to 4 for CD C
2
. The Reed-Solomon block can be programmed to make a severe check for “miscorrections”: This preselection will cause a reduction of the decoding performance.
THE ERROR CORRECTION ALGORITHM
The complete algebraic decoding algorithm for the errors and the erasures is summarized in the following steps:
STEP 1. Calculation of the syndrome S(z), the erasure locator polynomial E(z) and the calculation of the modified syndrome T(z). If r(x) is the received code word
S
j
=
∑
i
=
0
n
-
1
r
n
-
1
α
ji
If &agr;
jk
is the position of a k-erasure and e is the number of erasures
E
(
z
)
=
∏
k
=
1
e
(
1
-
z
α
jk
)
If t is the maximum number of errors the code is able to correct
T
(
z
)=
S
(
z
)
E
(
z
)mod(
z
2t
)
STEP 2. Perform the extended Euclidean Algorithm (modified version) to calculate the error locator polynomial &sgr;(z) and the error evaluator polynomial &ohgr;(z). Calculation of the new error locator polynomial &PSgr;(z)
&PSgr;(
z
)=&sgr;(
z
)
E
(
z
)
STEP 3. Perform the Chien search to find the roots of the new error locator polynomial. The roots of this polynomial indicate the error and erasure positions in a received code word. Perform the Forney's algorithm to find the error and erasure values.
STEP 4. Check the decoding process and correct the received code word.
The timing control block sets the control inputs of the Reed-Solomon block and send start syndrome pulse (start_synd) with the first symbol of the code word.
The en_synd is acting as an enable for the data bus (data_in).
Every erasure should be flagged by erasure_pos. During the shifting of the code word, the Reed-Solomon calculates its syndrome and its erasure polynomial.
Once the code word is completely shifted into the Reed-Solomon, the controller has to start the Key Equation Solver (start_kes).
The Reed-Solomon responds when error and location values are ready for the controller (kesready).
The errors and error locations are stored in a Lifo and the controller can read them with read_pos and read_error signals.
The Reed Solomon processing consists of three main tasks:
a) syndrome and erasure polynomial calculation (invoked by start_synd)
b) key equation solving and error calculation (invoked by start_kes)
c) Chien & Forney (generating the ending signal kes_ready)
as depicted in the block diagram of FIG.
8
.
In DVD Outer decoding, the erasure polynomial is equal for each column, because it is calculated using the incorrectable flag coming from the Inner decoding. For this reason it is calculated only once for each Ecc block of data at the beginning of the vertical decoding process; the resulting polynomial is stored depending on the store_eras_poly signal. This is depicted by way of a block diagram in FIG.
9
.
During the DVD decoding process (Inner-Outer-Inner-Outer- . . . ) the signal sel_eras_poly send to Key Equation Solver the current erasure polynomial (Inner) or the previous stored erasure polynomial (Outer).
SUMM
Andolina Giancarlo
Brenna Filippo
De Marzi Giuseppe
Ugioli Roberto
Abraham Esaw
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
De'cady Albert
Jorgenson Lisa K.
STMicroelectronics S.r.l.
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