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Servicing the TARGET Requests
6-7
6
service performed by the firmware is now complete. Finishing some
housekeeping, the firmware returns to the user service routine for the selected
LUN and gives it a final status code of $xx17.
If initiator is not supporting disconnect, no message-in phase and the TARGET
role returns an intermediate status $xx06 for command received.
If firmware is not enabled, the target role will response to ’inquiry’, ’request
sense’ commands with some meaningful data. Also, it will return "Not Ready"
to ’test unit ready’, ’send’, and ’send diagnostic’ commands. To all other
commands before target enabled, an ’Illegal request’ will be returned.
Now comes your turn to perform the required services.
The CDB that was received by the TARGET role firmware during the
command phase was stored in the command buffer that was allocated when
you issued the TARGET enable packet to the firmware. (The command table
pointer points to this command buffer; refer to the TARGET Enable Custom
Sequence Packet section in Chapter 2, words $08 and $0A -- command table
pointer.) You may wish to service the processor device standard commands
SEND ($0A) and RECEIVE ($08). The service of commands is totally
application driven. The SEND and RECEIVE commands are probably
sufficient to establish processor communication over the SCSI bus. Following
is an example of each service. "Example"
Example: Servicing the SEND command through the TARGET sequence
firmware packet.
STEP 1: Command Interpretation
Below is the CDB for a SEND command.
bit.....7...6...5...4...3...2...1...0...
byte 0 : 0 0 0 0 1 0 1 0 (OP CODE)
byte 1 : l u n - - - - -
(LUN|reserved)
byte 2 : Transfer length (M S byte) (Transfer
length)
byte 3 : Transfer length (middle byte) (Transfer
length)
byte 4 : Transfer length (L S byte) (Transfer
length)
byte 5 : v u - - - - f l (control
byte)