Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!sobeco!stacy
From: stacy@sobeco.com (s.millions)
Newsgroups: comp.sys.mips
Subject: Re: TCP/IP on RC6280
Keywords: trailers
Message-ID: <1991Jan13.214030.27744@sobeco.com>
Date: 13 Jan 91 21:40:30 GMT
References: <1991Jan9.144544.22626@sobeco.com> <4922@srava.sra.co.jp>
Sender: @sobeco.com
Organization: Groupe Sobeco, Montreal, Canada
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In <4922@srava.sra.co.jp> erik@srava.sra.co.jp (Erik M. van der Poel) writes:

>> I am having to turn off trailers on our
>> RC6280 so that it can talk to our DEC 20's.
>Do you have to turn off trailers on your RC6280 so that it *can* talk
>to your DEC 20's, or so that it talks *faster* to them?

It was done in an attempt to get them to talk, just talk. As it turns
out the trouble had nothing to do trailers. The MIPS device driver for
the eagle ethernet controller tries to do block mode transfers when
ever possible. If mbuf length is not a multiple of 32 bits, they will
ship out 1-3 bytes of random garbage at the end of the packet. The
dec 20s take the length of the ethernet packet - length of headers
and calculates its checksum on that, including the random chars
at the end which are not part of the data. As a result the dec 20
throughs out the packet. This was a nuisance to track down. As
luck would have it my login name and password made mbufs that
were multiples of 32 bits in length as were the files I transfered
as a test, so it would work for me, but not for others.

I have fixed this by brain damaging the device driver to not use block
mode on out bound packets. Will try a more elegant fix when time allows.

-stacy

-- 
"Sorry I had to plug you mister duck, but I'm a sportsman."    stacy@sobeco.com
    - Almyer Fudd                                            uunet!sobeco!stacy