Mips Technologies R4000 - Data ECC Generation

MIPS R4000 Microprocessor User's Manual 415
Error Checking and Correcting
Data ECC Generation
Each of the 64 data bits and 8 check bits has a unique 8-bit SECDED ECC
check code; this check code is generated by taking the even parity of the
ECC check code for a selected group of data bits. As Figure 16-1 shows,
bit locations are numbered from right to left in ascending order, from data
bit 0 (furthest right) to data bit 63 (furthest left). For example, data bit 0, in
the far right column of Figure 16-1, has an 8-bit check value of 0001 0011
2
(0s are represented in this figure by periods, (.), because they are not used
in the calculations).
Figure 16-1 also gives values for the 8 check bits, 7:0. For instance, the 8-
bit SECDED ECC code for check bit 6 is in column 6, near the right hand
edge of Figure 16-1.
Figure 16-1 Check Matrix for Data ECC Code
NOTE: * This row indicates the number of 1s in the generated syndrome for each data
bit in error.
. . . .
1111
1111
. . . .
1. . .
. 1. .
. . 1.
. . . 1
1. 1.
11. .
1. . .
1. . .
11. .
. 1. .
. 1. .
. 1. 1
. 1. .
11. .
1. . .
11. .
. . . 1
. . 11
. . 1.
. . 11
1. . .
1. 1.
11. .
1. . .
. 1. .
. 1. .
. 1. 1
11. .
1. . .
. 1. .
. . 1.
. . . 1
. . . .
. . . .
1111
1111
9876
6666
3210
55
98
5555
7654
55
32
5544
1098
4444
7654
4444
3210
3333
9876
3333
5432
3322
1098
2222
7654
2222
3210
1111
9876
1111
5432
3210
61 70 43 Check Bit
Data Bit
ECC
Code
Bits
Number of
1s in
syndrome*
3333 5511 3333 5511 3333 3333 3333 3333 3333 3333 3333 3333 3333 3333 5511 55113333 3333
27
27
27
27
27
27
27
27
11. .
1. . .
1. . .
1. 1.
. 1. 1
11. .
. 1. .
. 1. .
11. .
1. . .
11. .
. 1. .
. . 11
. . 1.
. . 11
. . . 1
1. . .
1. . .
1. 1.
11. .
. 1. .
. 1. 1
11. .
. 1. .
1. . .
. 1. .
. . 1.
. . . 1
. . . .
1111
1111
. . . .
. . . .
. . . .
1111
1111
1. . .
. 1. .
. . 1.
. . . 1
1111
. . . .
1111
. . . .
1. . .
. 1. .
. . 1.
. . . 1
1111
. . . .
. . . .
1111
1. . .
. 1. .
. . 1.
. . . 1
. . . .
1111
. . . .
1111
1. . .
. 1. .
. . 1.
. . . 1
1. . .
. 1. .
. . 1.
. . . 1
1111
. . . .
1111
. . . .
1. . .
. 1. .
. . 1.
. . . 1
1111
. . . .
. . . .
1111
1. . .
. 1. .
. . 1.
. . . 1
. . . .
1111
. . . .
1111
1. . .
. 1. .
. . 1.
. . . 1
1111
1111
. . . .
. . . .
54
11
10
1111
1111
. . . .
. . . .
1. . .
. 1. .
. . 1.
. . . 1
52
MSB
LSB
Data bit 0
Data bit 63
Check bit 6
Nibbles