Here's my reply to Ulrich. :-)

(Ulrich, if you're going to send your replies both to me, and to the list,
please do so in the same message! :-) That way I know if we're switching
to private EMail, or staying public. Also, then everyone gets to see all
sides of the conversation. :-)

Take care,

Bill

---------- Forwarded message ----------
Date: Thu, 22 Apr 1999 10:23:05 -0700 (PDT)
From: Bill Studenmund <wrstuden@nas.nasa.gov>
To: Ulrich Hausmann <ulrich.hausmann@a2e.hp.shuttle.de>
Cc: Bill Studenmund <wrstuden@sally.nas.nasa.gov>
Subject: Re: Serial Clock

On Thu, 22 Apr 1999, Ulrich Hausmann wrote:

> Bill,
> 
> isn't AppleTalk since the very first beginning at 230.400 bps? I think
> even a MacPlus ser port supported that speed. OTOH, as far as I know
> the ser port speed went down, if running at the same time networking
> and ser port connecting activities.

When Apple came out with EtherTalk, they renamed the serial port-based
networking to be LocalTalk.

Yes, it's running at 230400, but it runs in polled mode, not interrupt
mode as does the normal serial driver. So whenever a packet comes in, the
computer stops what it is doing and receives the packet.  NetBSD doesn't
support polled mode i/o.

> There are some programs (like ProTERM, FreePPP), allowing you to set
> the port speed higher than 57.6 and it seems to work - sometimes.

The "sometimes" is where my hesitancy comes from. :-) Sure you can SET the
rate that high, it just mightn't work well. :-)

> May I ask a somewhat related, but not NetBSD question (since you're a
> serial connection guru here :)) ): Would it be better to use a
> IIfx/Quadra 900/950 with the built in serial I/O controller on or off.
> In case of OFF FreePPP allows 230.400 bps (in case of ON only 57.600
> are accepted, possibly because the controller tells FreePPP so).
> Practically, with a LASAT 56K V90 modem attached, performance - to me,
> but it's only an impression - seemed better with the Serial Switcher
> set to ON and consequently port speed set to only 57.600.

Hard to say. If you feel the performance is better, leave it on. :-)

I'm not sure how muchn the iop's are used under MacOS, but they certainly
will help. The thing is that the 8530 has a 3-byte fifo. So you have to
receive the bytes fairly quickly. With an iop, it receives the bytes, and
then hands them off to MacOS at a leisurly rate.

Also, if a character ever gets dropped, then the whole PPP packet it was a
part of has to be re-transmitted. The faster the transmission, the more
likely a byte is to be dropped. If PPP is using an MRU of 1500 (it
receives packets up to 1500 bytes long), and you have a 1 in 3000 error
rate, about half of the packets will need to be re transmitted. So its
real important to not try to run the serial ports too fast. :-)

Take care,

Bill