Request for Message Codes

Gary Porter garyp at
Thu Sep 8 13:52:02 PDT 1994

Hi all -

Just a note to let you be thinking about this before the meeting in
Houston next week.

We will be requesting two new message codes, to support a translation
capability from parallel SCSI to some other protocol, such as FCP or SBP.
The serial protocols want to know the number of bytes to be transferred
and the direction. For standard SCSI commands, this is derivable from the
CDB and some knowledge of the Target type and its parameters (although it
is not trivial even for standard commands). For vendor unique commands,
there is no way to know without specific details of the exact model of

What we want is a message and response as follows :

Request Transfer Parameters message : an optional one-byte message which
requests the other party of the nexus to reply with a direction and size
of the expected data transfer related to the current command.

Transfer Parameters extended message : an optional extended message which
reports the expected direction and size of the expected data transfer for
the current command. The layout of the message is as follows :

	Byte 0 :		01 (Extended message)
	Byte 1 :		06 (remaining length)
	Byte 2 :		xx (Transfer Parameters message)
	Byte 3 :		?? (Direction of transfer)
	Byte 4-7 :	?? (Size in bytes of expected data transfer)

The Direction of transfer field is bit significant. Bit 0 says Data-Out
expected. Bit 1 says Data-In expected. With the current rules, a maximum
of one of these bits could be set. If both are 0, it says no data transfer
is expected, and the Size field must be 0.

The Size field is the number of bytes expected to be transferred in the
data phase(s) for the current command. (NOTE : do we need more than 4 bytes?)
This value is transferred MSB first.

We will be making (slightly) more formal presentation in Houston regarding
this matter.


Gary Porter                                    Voice      (415)322-5322
Ancot Corporation                              FAX        (415)322-0455
115 Constitution Drive                         E-mail   garyp at
Menlo Park, CA 94025                           Flames          >dev/nul

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