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(2)
Tagged Queuing
The host computer can issue plural commands for a logical unit by using the
Queue Tag message. The controller contains a single queue slot which can
enqueue SCSI commands from a single or multiple hosts up to 128 commands.
The controller selects a queued command and executes it based on the command
type of the Queue Tag message specified by the host computer.
The host computer can not issue a tagged command and an untagged command
at a same time, nor issue a duplicated tagged command ( Same tag Number ) at a
same time.
3.1.3 DISCONNECT / RECONNECT
This SCSI controller disconnects from and reconnects to the SCSI bus during
command execution to make up the SCSI bus available to other SCSI devices.
For the controller to disconnect, the host computer must take the following
actions :
· Sets the host computer ID bit for the SCSI ID bit in the SELECTION phase.
· Sets bit 6 (Disconnection/Reconnection Available) of the Identify message to 1
after the SELECTION phase.
· Receives the Save Data Pointer and Disconnect messages from the controller.
(1)
Disconnect
The controller disconnects from the SCSI bus when :
· It enqueues a command and cannot execute it immediately.
· It is occurred one of the following conditions and the SCSI Bus is held inactive
without handshaking :
(2)
Reconnect
The controller, once it disconnects from the SCSI bus, reconnects to the SCSI bus
whenever it becomes necessary to continue the current operation (normally
transfer data or report status).
For reconnect operation, the controller waits until SCSI Bus is free, and after it
gains control of the Bus by ARBITRATION and reselects the host computer.
This operation is repeated until the controller gains control of the Bus.
3 SCSI BUS
OEM MANUAL:K6602924
Revision: 1 / Date: 2003.03.06
Page: 32 / 273
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