The Wide Data Transfer Request message is used to negotiate the width of the data path for the data
transfers between the media changer and the initiator. The width applies to data phases only. The media
changer does not support wide data transfers. When it receives a WDTR message from the initiator, it
returns a WDTR message with a transfer width exponent of 0 (8-bit transfer width). The successful
exchange of WDTR message implies an agreement to an 8-bit data transfer width.
Bit 7 6 5 4 3 2 1 0
Byte
0 Extended Message (01h)
1 Extended Message Length (02h)
2 Extended Message Code (03h)
3 Transfer Width Exponent
The Transfer Width field determines the width of the data path for data transfers. The media changer will
return 00h for this field. This indicates that the media changer supports an 8-bit data transfer width only.
Save Data Pointers
The SAVE DATA POINTERS message is issued before every disconnect message following a data in or
data out phase. The message is not sent when disconnecting after a command descriptor block that did
not transfer data.
Restore Pointers
The media changer sends the RESTORE POINTERS message to direct the initiator to copy the most
recently saved command, data and status pointers of the I/0 process to the corresponding active pointers.
The command and status pointers are restored to the value at the beginning of the data area. The media
changer sends the Restore Pointers message after a detecting a parity error during the command phase
or data out phase. After the media changer successfully sends the Restore Pointers message to the
initiator, the media changer restarts the command, data in, data out, or status phase from the beginning.
Disconnect
The DISCONNECT message is sent by a target to inform an initiator that the present data transfer will be
suspended. the target will reselect the initiator at a later time to continue the current operation.
Initiator Detected Error
The INITIATOR DETECTED ERROR message is sent from an initiator to inform a target that an error
occurred. This allows the target to retry the operation.
Abort
The ABORT message terminates the current I/O process. The target goes directly to the BUS FREE phase
after receipt of this message.
Message Reject
The MESSAGE REJECT message is sent from the initiator or target to indicate that the last message
received was inappropriate or not implemented.
4-2 TL2000 and TL4000 SCSI Reference
To Next Page
Loading...
Need help?
General
