P1394 Mail Archive: Re: P1394> Re: Native SBP-2 Printer Profile?

P1394 Mail Archive: Re: P1394> Re: Native SBP-2 Printer Profile?

Re: P1394> Re: Native SBP-2 Printer Profile?

Greg Shue (gregs@sdd.hp.com)
Fri, 27 Feb 1998 12:12:29 -0800 (PST)

>
> Hi,
>
> I have a question regarding the necessity of buffer identifier (or
> sequence number) in the ORB command.
>
> In the Annex E. of SBP-2 Rev.3a, the following is described.
>
> E.4 Status FIFO write request
> When the target detects a missing acknowledgement after a write to
> an initiator's status FIFO, it should take no error recovery
> actions. Any target resources allocated to the ORB should be
> released by the target. The initiator is expected to discover the
> error by means of a higher-level mechanism, such as a command
> time-out and to initiate appropriate error recovery. The nature of
> the error recovery undertaken by the initiator likely depends
> whether or not the target processes ORB's and returns their status
> in order, but in any event is beyond the scope of this description.
>
> If this happened and followed by bus reset, it seems initiator loses
> synchronization with target. I suppose the sequence number or
> something may be useful in this situation to avoid duplicated ORB.
>
> Am I missing something?
>
> Akihiro Shimura

I know you caught something which I have missed. I wasn't fully
aware of this clause, and it certainly needs to be addressed to
deliver reliability.

The buffer identifier (or sequence number) helps filter out
redundant buffers, which solves part of the problem. The more
signficant issue is:

How does a PWG Imaging Communications Profile initiator
_detect_ that it should try to recover from a lost Status_FIFO
write acknowledge?

The Status_FIFO is written to:
A) at the end of every Management Agent request
(so this should be defined by SBP-2 for Management
Agent commands. I don't recall that it is.)

B) at the end of every request on the task list
(within the scope of the device profile)

C) as the mechanism for communicating Unsolicited Status

I'll be thinking about these for a while ...

-- 
Greg Shue
Hewlett-Packard Company
Office Products Division			gregs@sdd.hp.com
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