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Path: utzoo!mnetor!seismo!rutgers!ames!oliveb!pyramid!voder!blia!ted
From: ted@blia.BLI.COM (Ted Marshall)
Newsgroups: comp.periphs,comp.sys.dec
Subject: Re: Q-BUS DMA interprocessor links - DRV11-WA, DRQ11-C, DEQNA
Message-ID: <2673@blia.BLI.COM>
Date: Thu, 14-May-87 17:23:35 EDT
Article-I.D.: blia.2673
Posted: Thu May 14 17:23:35 1987
Date-Received: Sat, 16-May-87 13:28:52 EDT
References: <540@acer.stl.stc.co.uk>
Distribution: world
Organization: Britton Lee, Los Gatos, CA
Lines: 27
Summary: EC to DEQNA
Xref: mnetor comp.periphs:377 comp.sys.dec:194

In article <540@acer.stl.stc.co.uk>, scott@stl.stc.co.uk (Mike Scott) writes:
> 3. DEQNA The hardware is DMA, but VMS operation involves moving the data
> between system and user buffers (I think?) and is not efficient enough for my
> application. My experience anyway is that the DEQNA is not reliable enough- a
> test program using qio level calls to the DEQNA driver fell over regularly and
> frequently with an unexplained timeout error status.

The timeout error is due to a design problem in the deqna. The latest rev
of the card fixes this. I believe that DEC will exchange an old card for the
new (for a small charge if not under DEC maint.). On VMS, you need at least
version 4.4 to get a change to the driver that completes the fix.

However, I expect that you are right that the driver is too slow for your
needs. It is designed for use by multiple processes, receiving different
protocol types. This requires receiving into system buffers and then
copying into the user buffers. I suspect that this is not what you need.

Note also that for any of these devices, you need to use some sort of
protocol for retransmitting bad or lost packets. Even on a well installed
Ethernet with only the two stations, there is a non-zero chance of losing
a packet. This applies to just about any kind of inter-process link.

-- 
Ted Marshall       ...!ucbvax!mtxinu!blia!ted <or> mtxinu!blia!ted@Berkeley.EDU
Britton Lee, Inc., 14600 Winchester Blvd, Los Gatos, Ca 95030     (408)378-7000
The opinions expressed above are those of the poster and not his employer.
             "My hovercraft is full of eels" *fnord*