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Chapter 4 SCSI Interface
SCSI Message System
Command Complete
(00h)
Disconnect (04h)
Extended Message
(01h)
Table 12 Extended
Message Format
58
This message is sent from a target to an initiator to indicate that the
execution of a command (or a series of linked commands) is complete
4
and valid status has been sent to the initiator. After it has sent the
message successfully, the target goes to the BUS FREE phase by
releasing BSY. If received by the tape unit, it is handled as an illegal
message; the library returns MESSAGE REJECT and enters the STATUS
phase reporting CHECK CONDITION with the sense key set to
COMMAND ABORTED.
A target sends DISCONNECT to tell an initiator that the present
4
physical path is going to be broken (the target intends to disconnect by
releasing BSY). Later, reselection is required in order to complete the
current operation. This message does not cause the initiator to save the
Data pointer.
When received from an initiator, the library may respond in one of two
ways. First, it may take the message as a request by the initiator to
disconnect and comply by entering message in phase and sending the
DISCONNECT message back to the initiator (possibly preceded by the
SAVE DATA POINTERS message). In this case, it will delay a
minimum of 200 ms before arbitrating for the bus again. Alternately, it
may enter the message in phase and return MESSAGE REJECT.
This is sent as the first byte of a multiple-byte message (> 2 bytes) by
either initiator or target. EXTENDED MESSAGE has the following
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format:
Byte 0
Byte 1
Byte 2
Byte 3
The Extended Message Length specifies the length of the Extended
Message plus the number of additional parameter bytes that are to
follow. The length does not include bytes 0 and 1. A value of zero for
the Extended Message Length indicates 256 bytes to follow.
Possible Extended Message codes are:
00h - Modify Data Pointer (not supported)
01h - Synchronous Data Transfer Request
02h - Reserved
ATL PowerStor L200 Series Library User's Guide
Extended Message Identifier - 01h
Extended Message Length
Extended Message Code
Extended Message Additional
Parameters
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