Chapter 4. MessagesThe message system allows communication between the host and the media changer logical unit for thepurpose of physical path management.Description Code DirectionCOMMAND COMPLETE 00h InEXTENDED MESSAGES 01h In / OutSAVE DATA POINTERS 02h InRESTORE POINTERS 03h InDISCONNECT 04h InINITIATOR DETECTED ERROR 05h OutABORT 06h OutMESSAGE REJECT 07h In / OutNO-OP 08h OutMESSAGE PARITY ERROR 09h OutBUS DEVICE RESET 0Ch OutIDENTIFY 80h / C0h In / OutCommand CompleteThe COMMAND COMPLETE message is sent from a target to an initiator to indicate that the execution ofa command completed and a valid status has been sent to the initiator.Extended messagesThe library supports two extended messages: Synchronous Data Transfer Request (01h) and Wide DataTransfer Request (03h). All other extended messages are rejected with a Reject message after receivingthe entire Extended message. The SDTR is used to negotiate data transfer agreements. If the host wantsto transfer data synchronously it must negotiate a synchronous data transfer agreement with the targetbefore transferring data. The media changer does not support synchronous data transfer. When it receivesa SDTR from a initiator, it returns a SDTR message with a REQ/ACK offset equal to zero. This indicatesthat the media changer requires asynchronous data transfer.Bit 7 6 5 4 3 2 1 0Byte0 Extended Message (01h)1 Extended Message Length (03h)2 Extended Message Code (01h)3 Transfer Period Factor4 REQ/ACK OffsetThe Transfer Period Factor field indicated the value for the Transfer Period in 4ns counts. This value is notused, the returned value is 00h. The media changer returns 00h for the REQ/ACK Offset field indicatingthat the media changer requires asynchronous data transfer.4-1
