PS4210-1099
Page 5 of 30
Advanced Hardware Architectures, Inc.
2.4
RS DECODER
The RS block performs the outer decoding. The
Reed-Solomon decoder conforms to the DVB
specification. The RS block can be programmed to
decode t=1, 1.5, 2, . . . 7.5, 8.
The block length of the code is programmable
up to 255 bytes. Block length is 204 with 16 check
bytes and a correction power of 8 bytes per block
for the DVB specification. Maximum latency
through the RS Decoder Block is:
2.5
DERANDOMIZE/ENERGY
DISPERSAL
The derandomizer is specified in the DVB
specification. It is built as a 15 stage pseudo-
random binary sequence generator with
initialization sequence specified by RSEED0 and
RSEED1 registers. The randomization occurs over
8 blocks of MGSBYTES2 (188 bytes for DVB
specification). Randomization does not occur over
Reed-Solomon parity bytes nor sync bytes.
However, the pseudo-random binary sequence
generator continues to run during non-inverted sync
bytes. Maximum latency = 10 VCLKs.
2.6
MODES OF OPERATION
The FEC decoder has been designed with a
modular approach so that each of the four major
functions: Viterbi decoding, deinterleaving, RS
decoding and derandomization can be individually
enabled or disabled. Five operating modes are
supported by the device. These are:
1) Normal mode. All functions enabled. Inputs
clocked with SCLK.
2) Byte Input mode. All functions except Viterbi
enabled. Inputs clocked with VCLK. Tie
SCLK to VCLK. Use Byte [1:0], I[2:0] and
Q[2:0] as byte wide data path. Bytes must
arrive on packet boundaries.
3) Viterbi decode mode. Inputs clocked with
SCLK.
4) Reed-Solomon decode mode. Same input
constraints as byte input mode.
5) Deinterleave mode. Same input constraints as
byte input mode.
These modes may be operated with or without
the derandomizer enabled.
Table 1:
Various Modes Supported by the AHA4210 Device
Table 2:
Register Settings for Functional Block Bypass
px
()
x
8
x
4
x
3
x
2
1
++++
=
gx
()
x
α0
+
() x α1
+
(). . . x α 2t 1
–
()
+
()
=
α1
primitive element
=
N
1
–
() 8120 2RN 2.67
×
++
+
×
MODE
FUNCTIONAL BLOCK
VITERBI
DEINTERLEAVER
RS DECODER
DERANDOMIZER
1) Normal
Enabled
Enabled
Enabled
Either
2) Byte Input
Disabled
Enabled
Enabled
Either
3) Viterbi Decode
Enabled
Disabled
Disabled
Either
4) RS Decode
Disabled
Disabled
Enabled
Either
5) Deinterleaver
Disabled
Enabled
Disabled
Either
FUNCTIONAL BLOCK
ENABLED
DISABLED
Viterbi
VCON[4]=1
IOCNTRL[2]=0
VCON[4]=0
IOCNTRL[2]=1
Deinterleaver
JDEPTH[4]=1
JDEPTH[4]=0
Reed-Solomon
RSCONTROL=0C
RSCONTROL=1C
Derandomizer
IOCNTRL[7]=1; VCON[7]=1
IOCNTRL[7]=0; VCON[7]=0
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