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Chapter 4:
Frame ECC Logic
S[11]
S[11]
In case of a single-bit error in the frame data, the syndrome bits S[10:0] points to the flipped
bit in the address space from 704 (location of the first bit in the frame) to 2047 (last bit in the
frame). To convert the syndrome value S[10:0] to the index of the flipped bit in the range 0
to 1311, subtract 704 decimal (2C0 hexadecimal or 01011000000 binary) if the syndrome
is less than 1,024 decimal; otherwise, subtract 736 decimal (2E0 hexadecimal or
01011100000 binary). This is equivalent to subtracting 22 or 23 decimal from S[10:5], and
can be calculated as bit_index = {S[10:5] –6'd22-S[10],S[5:0]}.
If S[10:0] is 0 or a power of 2, however, an error in a parity bit has occurred. The Hamming
parity bits are stored in locations 640-651. If bit S[11] indicates a single-bit error, then (in the
case of a Hamming code parity bit error) a 1 is presented in the appropriate power-of-2 bit
position, with the other syndrome bits set to 0:
100000000001 ->
100000000010 ->
100000000100 ->
100000001000 ->
100000010000 ->
100000100000 ->
100001000000 ->
100010000000 ->
100100000000 ->
101000000000 ->
110000000000 ->
100000000000 ->
76
=
=
0: single-bit error; overall parity bit p[11] is in error.
1, S[10:0]
=
≠
0: double-bit error, not correctable.
0, S[10:0]
640
641
642
643
644
645
646
647
648
649
650
651
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Virtex-4 FPGA Configuration User Guide
UG071 (v1.12) June 2, 2017
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