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From: moroney@jon.dec.com
Newsgroups: net.lan
Subject: Re: Need help with DEQNA
Message-ID: <4330@decwrl.DEC.COM>
Date: Mon, 21-Jul-86 22:23:45 EDT
Article-I.D.: decwrl.4330
Posted: Mon Jul 21 22:23:45 1986
Date-Received: Wed, 23-Jul-86 04:32:41 EDT
Sender: daemon@decwrl.DEC.COM
Organization: Digital Equipment Corporation
Lines: 41

>I am attempting to write a driver for the DEQNA and I'm having some 
>problems.  My current problems relate to getting it into "promiscuous"
>mode.  The manual is very vague on exactly how to set up the transmit
>bdl's byte count.  This is a negative (2s comp) value for a normal transmission.
>What should the format be set up for a setup packet?  The book talks about
>a value greater than 128.  Is that positive 128 or negative 128?

That same area of the manual confused me, too.  Use the exact same rules as
normal BDL's.  For example, to place the QNA into promiscuous mode, take the
bit value of the "promiscuous" bit (i.e. 2), add 128 (200 octal), and this
gives 130 (202 octal).  Now, you have the "byte count" that's interpreted
differently.  You now divide by 2 to get a word count, in this case 65 (101
octal).  Since the byte count was even, we clear the "start on odd byte" bit
(bit 7 of second word of the BDL).  Then negate the word count, so you get
177677 octal which is what you insert in the length word of the BDL (fourth
word of BDL).  Feed this packet to the QNA, and you are set.  Be sure you give
it a valid address in the BDL as well, since it loads the network address table
in anyway, even though it isn't needed in this case. 

Rest assured, a new manual is in the works.

>The setup packet is bad news.  The engineers who designed this beast 
>must have something against software people.  Organizing the packet in that 
>format (addresses in COLUMNS in an array, with strategic areas of zeroes 
>scattered about) is quite anti-social.  How much did that save you in hardware
>costs, guys?  A whole $0.15?

I believe the person who did the QNA design was a hardware engineer who knew
knew little about software, so he didn't realize he was making life difficult
for hundreds of programmers in the future.  The table format you see is how it
is stored inside the QNA, and he saw no reason to change it.

>I am also quite concerned about missing interrupts.  This comes from personal
>experience with looping back a setup packet.

Hmm...  Did you set the "interrupt enable" bit?  Is the CPU priority low enough
to allow interrupts?  Remember, the QNA needs time to DMA the data, too.

-Mike Moroney

..decvax!decwrl!rhea!jon!moroney