P1394 Mail Archive: Re: P1394> Print Protocols

P1394 Mail Archive: Re: P1394> Print Protocols

Re: P1394> Print Protocols

(no name) ((no email))
Thu, 19 Feb 1998 10:54:19 -0800

Eric, Greg, Brian ...

I really like the way this discussion is shaping up, but I have one small
comment on the following:

At 3:11 PM -0800 2/17/98, Eric Anderson wrote:
>would suggest that generally whatever device has initiated the
>operation is the initiator (simple, huh?). In the scanner-printer
>case, probably we pressed a button on the scanner to cause it to
>print the image. So the scanner is the initiator in this case.

Actually, I think it is a bit more complicated.

1) In SBP-2, most of the pacing (flow control) is done by the target (it's
the target that fetches the ORBs and decides exactly when to do the data
transfer), it is best for the device that has the most constraints on
timing to be the target. It's a toss-up between a scanner and a printer,
but between a CPU and a printer *or* a scanner, it's the CPU that has the
most relaxed timing, so it should be the initiator.

2) Devices that have a natural memory model (CPUs come to mind) should be
initiators, since that allows them to implement a simple bus bridge
function to support the target read and write operations directly, without
software intervention.

Michael D. Johas Teener, Chief Technical Officer & Chairman of the Board
Zayante, Inc., 269 Mt. Hermon Rd. #111, Scotts Valley, CA 95066-4000, USA
email: mike@zayante.com voice: +1-408-461-4901 fax: +1-408-461-1394
======================== http://www.zayante.com ===========================