MIPS R4000 Microprocessor User's Manual 419
Error Checking and Correcting
6. Using the data in Figure 16-1, it may be possible to correct either
the data bit or check bit in error. Determine if the syndrome is in
Figure 16-1 by counting the number on 1s in the syndrome.
• If the syndrome contains either one, three, or five 1s,
the syndrome is in Figure 16-1. Three or five 1s
indicates that at least one data bit is in error. A single 1
indicates an ECC check bit is in error.
• If the syndrome contains two 1s, a double-bit error has
been detected, located in two consecutive bits of a
nibble. This is not correctable.
• If the syndrome contains four 1s, a 4-bit error has been
detected, located in four consecutive bits of a nibble.
This is not correctable.
If the syndrome is identical to any of the syndromes in the Figure
16-1, the column number of that data or check bit indicates the
location of the bit in error. The bit that is in error is corrected by
inverting its state (a 1 is changed to 0; a 0 is changed to 1).
The following sections show how to use the check matrices in Figure 16-1
for detecting:
• single data bit error
• single data check bit error
• multiple data bit errors (2 consecutive bits in a nibble)
• multiple data bit errors (3 consecutive bits in a nibble)
• multiple data bit errors (4 consecutive bits in a nibble)
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