Arbitration Phase; 1.6.2.1 Normal Arbitration - Fujitsu MBA3073 SERIES Technical Manual

The SCSI bus enters the BUS FREE phase when the TARG stops the BSY signal in one of the
following events:
•
When RESET condition has been detected.
•
When TARG has received the following message normally.
ABORT TASK, ABORT TASK SET, CLEAR TASK SET,
LOGICAL UNIT RESET, TARG RESET, CLEAR ACA
•
When TARG has transmitted the following message normally.
DISCONNECT, TASK COMPLETE
•
When a transceiver mode change.
•
When the release of the SEL signal after a SELECTION or RESELECTION phase time-out.
In any case other than above, if the TARG negates the BSY signal to enter a BUS FREE phase,
the TARG informs the INIT that it has detected an ERROR condition of the SCSI bus. The
TARG can enter a BUS FREE phase forcibly regardless of ATN signal status; the INIT must treat
that phase transition as indicating the abnormal end of command. The TARG clears all hold data
or status and terminates the command being executed. It can then create sense data indicating the
detailed error condition. If the INIT detects a BUS FREE phase when it is not expected, it should
issue a REQUEST SENSE command to read the sense data.
1.6.2

ARBITRATION phase

1.6.2.1 Normal ARBITRATION

The ARBITRATION phase allows one SCSI device to gain control of the SCSI bus. The SCSI
device that gets control of the SCSI bus can start the operation as INIT or TARG.
This is an optional system bus phase. This phase is required for the system that has two or more
INITs or uses the RESELECTION phase.
Arbitration is mandatory and requires the detection of a Bus Free phase on the SCSI bus before
starting.
SCSI device with arbitration fairness enabled shall maintain a fairness register which records the
SCSI IDs of devices that need a chance to arbitrate. (see 1.12).
Fairness in arbitration is enabled in targets by the Disconnect-Reconnect mode page.
Figure 1.26 shows the ARBITRATION phase, and the following explains how the SCSI device
gets control of the SCSI bus.
1) The SCSI device shall wait for BUS FREE phase. (see Section 1.6.1).
2) The SCSI device shall wait at least Bus Free Delay after the BUS FREE phase detection
before driving any signal.
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