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1.7.6
Reset Processing
The means which the INIT can use to reset the SCSI bus are shown below.
•
RESET Condition
•
BUS DEVICE RESET Message
•
CLEAR QUEUE Message
•
ABORT Message
•
ABORT TAG Message
The RESET condition resets all the SCSI devices connected on the same SCSI bus. The IDD
is initialized to the same state as when its power is switched on by the RESET condition, with
the currently executed command as well as all the commands in the queue cleared.
The BUS DEVICE RESET message resets a specific SCSI device (TARG), selected by the
INIT, only and can initialize that TARG to the same state as when its power is switched on,
but in a multi-initiator environment, caution concerning clearing of commands issued by other
INITs is necessary.
The CLEAR QUEUE message causes the IDD to clear the currently executed command and
all the commands in the queue. The previously set environment and conditions, such as
MODE SELECT parameters, are not changed.
An INIT which wants to clear only specific commands it has issued itself must use an ABORT
message or an ABORT TAG message. In this case, the INIT generates an ATTENTION
condition at the desired point in time if that command is currently being executed on the SCSI
bus, then sends the ABORT message to the TARG. Also, if there is a disconnect in effect,
after the INIT selects the TARG, an ABORT message, in the case of an untagged command, or
an ABORT TAG message, in the case of a tagged command, is sent following an IDENTIFY
message which specifies the object logical unit, or the INIT waits until a reconnection request
occurs, then sends an ABORT message or ABORT TAG message. In the case of an ABORT
message, only the commands issued previously in the logical unit specified at that time by the
INIT that issues the ABORT message (currently being executed or in the queue) are cleared
and there is no influence on the other commands.
When an ABORT TAG message is received, only the command issued to the logical unit
specified at that time by the INIT which issued the ABORT TAG message is cleared, and there
is no influence on the other commands. No status byte or COMMAND COMPLETE message
is reported concerning commands cleared in this processing.
In particular, in the case of clearing of a write operation command for writing to the disk
media which is currently being executed, the IDD cuts off processing of that command as
shown in Table 1.6. The case of halting an overlapping command that is currently being
executed (see item 1.7.1) is the same. The INIT must determine the complete completion state
and if necessary, must execute data recovery processing.
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C141-E039-01EN
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