P1394 Mail Archive: P1394> unordered execution

P1394 Mail Archive: P1394> unordered execution

P1394> unordered execution

Nagasaka Fumio (Nagasaka.Fumio@exc.epson.co.jp)
Mon, 9 Mar 1998 10:14:15 +0900

Does SBP-2 printing protocol need to have out of order execution for ORB

Let me assume one case shown below.
When an initiator puts an input ORB in linked list of ORBs.
[out::ORB] - [out::ORB] - [out::ORB] - [in::ORB] - [out::ORB] …
If our SBP-2 target consume them by in order execution. The target
will stop at fourth ORB and will examine whether it has reverse data
or not. It is normal and reasonable.
We might have an analogy of C language source code outlines
putchar(..); // step 1
putchar(..); // step 2
putchar(..); // step 3
getchar( ); // step 4 * INPUT*
putchar(..); // step 5
This process will stop at step 4 and will wait input from TTY.

OK?, next, let’s go back to SBP-2 target problem. Even if
the target does not have any thing to replay at step 4. The
transport layer shall *not* return “no data flag” or “something
to say there is nothing to reply”. The target’s application may reply
“no data” , “this is data” or any thing. This action shall be taken
by application’s responsibility.

By the way, for second case is shown below.
When the initiator has some requests which shall be delivered to
each logical channels like these,…(#k means logical channel ‘k’).
[out::#1::ORB] - [out::#1::ORB] - [out::#1::ORB] - [in::#2::ORB] -
[out::#1::ORB] …
Then if the transport layer in the target waits reverse data is passed
through from the application, fifth ORB which shall be delivered to
channel #1 will not be delivered while the transport is pending on
fourth ORB.

If our SBP-2 protocol may allow out of order execution. The
target is able to consume sixth ORB earlier than fifth. Then
the protocol provides concurrent executive opportunity for
each logical channels.

* Shall the transport provide out of order execution ?

I want to say no. The initiator shall place [input::ORB] if
it expects reverse data will be sent from the target. I would
like to say, the currents SBP-2 protocol has enough facility.

I am curious why unordered execution is required for ‘HPT’.
May be there are something I am missing.

Thank you, best regard.
Fumio Nagasaka
Epson Software Development Laboratory Inc.
Tel +81 268 25 4111, Fax +81 268 25 4627
E-mail to nagasaka.fumio@exc.epson.co.jp