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From: tim@normac.UUCP.UUCP
Newsgroups: mod.protocols.appletalk
Subject: Re: Mac, Sun sharing LaserWriter?
Message-ID: <8605300013.AA28576@ucbvax.Berkeley.EDU>
Date: Thu, 29-May-86 15:37:13 EDT
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Posted: Thu May 29 15:37:13 1986
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Re: the Sun CPU's 8530 SCC chips

The presence of a Zilog 8530 chip is not sufficient to implement
AppleTalk. The following requirements must also be met:
1) It must be possible to clock the bitstream at 230,400
bits per second which usually means an external crystal oscillator
at either this frequency or some multiple (but not faster than 4 MHz).
2) AppleTalk is implemented over RS422 which requires balanced line
drivers and balanced receivers.  Since this isn't required for SCC
chips doing RS232, SCC-using circuits may not have these extra
wires in place.
3) To meet the AppleTalk spec, a filter/T-configuration of resistors
and caps is required between the line drivers and the AppleTalk
connector kit transformer.
4) Since the 8530 has limited buffering and AppleTalk is a synchronous
protocol, somebody has to monitor those buffers to keep the 8530 shifting
complete packets of bits in and out without overrun or underrun.
It works out to be about 35 usec per byte. This normally requires a
dedicated processor because bus latency and task switching often eat
up more time than this.
"Hey, I'm a software guy", so Stephen Lewis helped me succinctly
state the above.
My rumor source said that Sun looked at this, figured out what
was needed and decided not to do it at this time.

Re: NFS for the Mac

It's true. We have done a good paper design and have had some preliminary
talks with Sun and Apple about doing an NFS implementation for the Macintosh.
There are some hard problems surrounding file/directory naming which still
need to be worked out. Our goal would be to run without modifications to
either the Mac's HFS/AFP environment or any vanilla NFS server.
This would enable the Mac to be an NFS client only and we don't plan on
allowing NFS clients to be served by AFP servers using this design.
All the work would be done in the Kinetics gateway; the gateway program will
essentially be an AFP server and NFS client and do session bookkeeping,
all command driven from the AFP client. The gateway would need the full
112k RAM expansion, and possibly larger PROMs in the sockets. We are
estimating that it is a 5-6 man-month project if WE do it, but more
exploratory work needs to be done. We haven't started just yet.
We hope to get to it "real soon now" and this is not an officially
announced product for us. I don't think AFP has been announced by Apple either.

Re: MacWorkstation

The MIS group at Apple has converted MacWorkstation to use AppleTalk
through our gateway to Ethernet hosted on a Vax running VMS....

tim