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7.5.11 Time monitoring feature
The ODD has a time monitoring feature for the SCSI bus to prevent hang-up of the SCSI bus in
the case that the TARG cannot receive a response from the INIT in the RESELECTION or
INFORMATION TRANSFER phase.
(1) Time monitoring in RESELECTION phase
The ODD monitors the time of the response (BSY signal) from the INIT in the RESELECTION
phase. When the INIT does not send the BSY signal within a specified period, the ODD
executes the timeout process (see Subsection 7.5.4) to free the SCSI bus and then executes the
retry process (see Section 3.1) of the RESELECTION phase.
(2) Time monitoring in INFORMATION TRANSFER phase
The ODD monitors the timing of the ACK signal against the REQ signal in the INFORMATION
TRANSFER phase. Time monitoring is executed during the following period:
• ECOMMAND, STATUS, or MESSAGE phase:
Time taken from the moment of sending the REQ signal of the first byte to the moment of
completing the reception of the ACK signal of the last byte of the phase.
• DATA phase:
Time taken for completing eight REQ/ACK handshakes (average).
Note:
When the ACK signal is returned repeatedly within an interval of 500 ms or more, timeout
may occur even if eight REQ/ACK handshakes on average had been terminated with the
time listed in Table 7.9.
When timeout is detected, the ODD clears the command being executed and forces the SCSI bus
into the BUS FREE phase (see Section 3.1).
Table 7.9 Setting value of SCSI time monitoring
Monitoring time in
INFORMATION
TRANSFER phase
Monitoring time in
RESELECTION phase
Number of retries in
RESELECTION phase
About 30 sec About 250 ms 10 times