P1394 Mail Archive: Re: P1394> Print Protocols

Re: P1394> Print Protocols

Greg Shue (gregs@sdd.hp.com)
Thu, 19 Feb 1998 12:40:32 -0800 (PST)

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> > "Actually, I think it is a bit more complicated."
> >
> > Flow control:
> > If "flow control" refers to the scheduling of bus transactions to
> > process a task, then I agree it is done by the (target's) fetch
> > agent.
> >
> > If "flow control" refers to the presentation of the task requests
> > (ORBs) and shared memory space then it is managed the initiator,
> > since we're talking about one task request (ORB) referring to one
> > "packet" transfer.
> >
>
> Actually a single ORB can point to a data buffer which is larger than the
> maximumlegal 1394 packet transfer size. Therefore multiple data packet
> transfers can be
> caused by one ORB.

Ah, another case of overloaded terms. Yes, an ORB can refer to
a much larger data buffer than the maximum possible MTU of the bus.
This results in many MTU transfers per ORB. Thanks for keeping me
honest and consistent.

I was using "packet" with respect to the transaction layer.
I was thinking of the case where a 10 MByte print job is consumed by
a device with 1 MByte of buffer space, and the flow of data into the
1 MByte buffer space must be controlled. In this case I was thinking
that ORBs with 0.5 MByte to 1 MByte data blocks would be reasonable.

> Jack Hollins
> ASIC Architect
> Adaptec

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