Cray CRAY-1 - Error Correction Matrix

BYTE 0 BYTE 1 BYTE 2
BYTE 3
,---~---.
_---A-....-
,
,..----_----A..-... _____ ,
,-- __ --------A ____ "
0
1 2 3 4
5 6 7 8 9 10 11 12 13 14 15
16 17
18 19 20 21
22 23
24 25 26 27 28 29 30 31
x x
x x x x x
x
x
x
x
x
x x
x
x x x
x
x
x x
x
x
x
x
x x
x
x
x
x
x
x
x x x x x
x x
x
x
x x
x x
x
x x x
x
x
x
x
x
x
x
x
x
x
x
x
x x
x x
x
x x x
x x x x x x x x
x x x
x
x x
x
x
x x
x x x
x x x
x x x x x x x x
x x x x x x x x
x
x
x x
x
x x x
x x x x x x x x
x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x
X
BYTE 4
BYTE
5
BYTE 6 BYTE 7
~--, (-----.----~---,
..A
r
32 33 34 35 36 37 38 39
40 41
42 43 44 45 46 47
48 49 50 51 52 53 54 55 56 57 58 59 GO 61 62 63
x
x
x
x
x
x
x x
x
x
x
x
x
x
x x
x
x x
x
x
x x
x
x
x
x
x
x
x
x x
x
X
y.
X X
X
X
X
x
x
x
x
x
x
x
x
X
X
X X
X X X X
X X X
X
X
X X
X
x
x
x
x
x x x
x
X
X
X
X
X
X
X
X
X X X X X
X
X X
x x x
x x x x
x
X
X
X
X
X
X X
X X X X
x x x
x
X
X
X
X
X
X X
X
X
X X X x
x
x
x
X X
X X
X
X
X
X
X
X X X
x
x x
x
X
X
X X X X X
X
X
X X
X
x x x
x
CHECK BYTE
,---_--..A~ ____ ~
64 65 66 67 68 69 70 71
x
x
x
x
x
x
x
Figure 5-3. Error correction matrix
The states of these "5" bits are all symptoms of any error that occurred.
The matrix is designed so that any change of state of one data bit will
change
an odd number of syndrome bits. An error in two columns changes
the
parity states of an even number of bit groups. Therefore, a double
error appears as an even number of syndrome bits set to 1.
The matrix is designed so that SEeDED decodes the syndrome bits and
determines the error condition using the following
1.
If all syndrome bits are 0, no error occurred.
2. If only one syndrome bit is 1, the associated check bit
is in error.
2240004
5-7
E
so
S1
S2
53
54
55
56
S7