Chapter 4. Messages
The message system allows communication between the host and the media changer logical unit for the
purpose of physical path management.
Description Code Direction
COMMAND COMPLETE 00h In
EXTENDED MESSAGES 01h In / Out
SAVE DATA POINTERS 02h In
RESTORE POINTERS 03h In
DISCONNECT 04h In
INITIATOR DETECTED ERROR 05h Out
ABORT 06h Out
MESSAGE REJECT 07h In / Out
NO-OP 08h Out
MESSAGE PARITY ERROR 09h Out
BUS DEVICE RESET 0Ch Out
IDENTIFY 80h / C0h In / Out
Command Complete
The COMMAND COMPLETE message is sent from a target to an initiator to indicate that the execution of
a command completed and a valid status has been sent to the initiator.
Extended messages
The library supports two extended messages: Synchronous Data Transfer Request (01h) and Wide Data
Transfer Request (03h). All other extended messages are rejected with a Reject message after receiving
the entire Extended message. The SDTR is used to negotiate data transfer agreements. If the host wants
to transfer data synchronously it must negotiate a synchronous data transfer agreement with the target
before transferring data. The media changer does not support synchronous data transfer. When it receives
a SDTR from a initiator, it returns a SDTR message with a REQ/ACK offset equal to zero. This indicates
that the media changer requires asynchronous data transfer.
Bit 7 6 5 4 3 2 1 0
Byte
0 Extended Message (01h)
1 Extended Message Length (03h)
2 Extended Message Code (01h)
3 Transfer Period Factor
4 REQ/ACK Offset
The Transfer Period Factor field indicated the value for the Transfer Period in 4ns counts. This value is not
used, the returned value is 00h. The media changer returns 00h for the REQ/ACK Offset field indicating
that the media changer requires asynchronous data transfer.
4-1
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