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Service Information
7957 A/7958A
If the error rate tests are initiated via CS/80 using the 'send execution message'
option, errors are reported immediately to the host and are not logged to the
ERT log.
Both 'send execution' and 'no execution' ERT utilities keep a count of the sectors
successfully read by individual heads. The sectors read count is read by the host
through the read ER T log command.
4-47.
Error Byte Description
The error byte is used by error rate test utilities and by the run time log to report
the location of a data error and its severity to the host.
error byte format:
bit 7
byte sync (no data sync or sector overrun)
bit 6
error in header field
bit 5
error in data field
bit 4
=
unrecoverable data error
bit
3
bit
2
bit
1
bit
0
=
=
=
(all retries exhausted)
ECC marginal data error
retry marginal data error
(more than 1 retry required)
recoverable on the first retry
FIFO data lost or track offset invoked
bits 5-7 describe the location
bits 1-4 describe the severity
Bit 0 of the error byte serves two functions.
(1)
If bit 0 and bit 1 are set simultaneously, a FIFO data loss has occurred during
a write operation. This is a condition from which the write firmware can
recover. It is reported because a high frequency of occurrence can affect
drive performance. None of the location bits will be set.
(2) The second function is reported when bit 0 is set along with bit 2, bit 3, or
bit 4. This implies that the head had to be moved off track center to
successfully read data. The error location and severity are accurate.
Note: The recoverable bit (bit
1)
will not be set when bit 0 signifies track offset
used for data recovery. This is because the first retry is always performed on
track center. The two definitions for bit 0 are reported in a unique way so
that there should be no confusion as to which meaning to assign to bit 0 if
ERT's are run in send execution message mode.
(Confusion can occur when error bytes are "ORed" together in an ERT log
entry.)
If a data error occurs more than once at the same location (i.e., same physical
cylinder, physical head, and logical sector) on the disc, the error byte is 'OR'ed to
give a cumulative report, and the occurrence count is incremented.
4-29
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