Quantum ATL PowerStor L200 Series, User Manual

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Chapter 4 SCSI Interface
SCSI Message System
58 ATL PowerStor L200 Series Library User’s Guide
Command Complete
(00h)
4
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
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
.
Disconnect (04h)
4
A target sends
DISCONNECT
to tell an initiator that the present
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
.
Extended Message
(01h)
4
This is sent as the first byte of a multiple-byte message (> 2 bytes) by
either initiator or target.
EXTENDED MESSAGE
has the following
format:
Table 12 Extended
Message Format
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
Byte 0 Extended Message Identifier - 01h
Byte 1 Extended Message Length
Byte 2 Extended Message Code
Byte 3 Extended Message Additional
Parameters