msc@qubix.UUCP (07/07/83)
A short time ago I sent out a request for information about
3Com and Interlan ethernet interfaces. Here is a summary of
the responses I received. I'd like to thank the following
people for their replies.
Steve Bellovin mhb5b!smb
??????? alberta!steve
John DeTreville allegra!jdd
Steve Daniel mcnc!swd
Peter Gross hao!pag
??????? ztil!uh
Mark Horton cbosgd!mark
Jim Rees uw-beaver!jim
3Com Wins
---------
They work reliably.
They are easy to program.
The company is moderately helpful.
The documentation is reasonably good.
Supported by 4.2bsd
The head of the company, Bob Metcalf, is one of the inventors
of ethernet.
3Com Losses
-----------
The board does not use DMA. They include dual ported memory
and require 32k of address space on a Unibus or 8k on a multibus.
This is not much of a problem on a small 11 or on a multibus
but is a big loss on a Vax due to the overhead of passing all
the data through the unibus adapter. One respondent called it
a "major cpu sink"
You have to be careful that this dual-ported memory is not
detected by the system as simple main memory. One respondent
reports getting the C pre-processor loaded into his 3Com memory!
The board does not retry after collisions. It merely
interrupts you to tell you about the collision.
The destination id must be checked by software. Each packet on
the net interrupts. (This was reported for a Q-bus version; I
suspect that it applies to all versions.)
On a vax 750, you can't plug the board into a transceiver while
the system is running. The 15v supply can't handle the inrush
current.
The Unibus board is "not very compatible" with 4.1bsd
autoconf.
Interlan Wins
-------------
The documentation is very good and very extensive.
It's easier to program than the 3Com because it does more. One
respondent reports writing a driver in "just a couple of evenings"
(hacker-all-nighters or regular?????)
The different loopback modes are very useful in debugging.
BTL's Unix producers have chosen this as the board they will support.
It uses DMA to grab and return the packets to the system.
It does its own retries.
It is supported by 4.2bsd
Interlan Losses
---------------
It eats too much 15v supply. Interlan say this problem is now
fixed. The problem means that on a vax 750 you can't plug the
board into the transceiver while the system is running. The
15v supply can't handle the inrush current.
Interlan are not good about firmware fixes. One respondent
reports trying to use non-working boards for several months.
It turned out that Interlan had known about the problem for
a long time but had failed to tell new purchasers.
Early revisions of the firmware (< v2.0) have problems with
xmit packets getting mixed up with rcv packets. Rcv packets
come in garbled but with no checksum error reported.
Summary
-------
Each board has its own set of problems. Overall though the
consensus seems to be that the Interlan board is better
for a Vax and the 3Com for small 11's and multi-bus. On
systems such as the Sun, you don't gain anything from the
dma because the fast main memory is on a second bus. You
therefore have to copy the data from one set of memory to another
anyway.
We are going to use Interlan for both our Vax and our Suns.
We have already used up the 1MB of multibus address space
on our Suns so we don't have much choice.
--
Mark
...{decvax,ucbvax}!decwrl!qubix!msc
...{ittvax,amd70}!qubix!msc
decwrl!qubix!msc@Berkeley.ARPAdarrelj@sdcrdcf.UUCP (07/09/83)
Does anyone know anything about other Ethernet interfaces for Unibus, especially The ACC IF-11/Ethernet, the Able Easyway Ethernet and DECs new Ethernet interface board. I've seen the manufacturers literature on all of them (prices ~$4000, not set and $3500 respectively); all are DMA, the ACC board has firmware to do much low-level stuff. Would it be worth using the DEC board just to save finger pointing when things break? On VAX 750 problems with +15v power inrush preventing hooking up tranceiver while system is running: has anyone tried using different brands of transceiver? (Xerox has the cheapest I've seen, $200; theirs mounts different than most; you clamp on a threaded bushing at right angles to coax, drill a small hold thru shield, then screw the entire tranceiver into the hole; if you want to buy one, try Xerox Office (Systems or Products) Division). Dr. Darrel J. Van Buer (213)820-4111x5449 SDC