Date: Fri, 23 Feb 1996 11:10:03 -0600 (CST) From: Joe Greco <jgreco@brasil.moneng.mei.com> To: petzi@zit.th-darmstadt.de (Michael Beckmann) Cc: hackers@freebsd.org Subject: Re: 230.400 bps on serial port Message-ID: <199602231710.LAA13363@brasil.moneng.mei.com> In-Reply-To: <v02140b01ad534a96521f@[130.83.63.13]> from "Michael Beckmann" at Feb 23, 96 11:49:56 am
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> Hello Hackers,
>
> I need a reliable data transfer rate of 230.400 bps on the serial port for
> PPP. Can that be done ? getty only has a setting for 115.200 bps. I have a
> Gigabyte 586 ATEP mainboard with FIFOs. Can I use them for 230.400 bps, and
> how ? Or should I buy a special serial card for that ?
>
> Thanks,
A standard 16550 in normal PC configuration has a maximum port speed of
115,200bps. It can't go at any faster usable speed because you're already
at the smallest usable divisor.
If you have a real 16550 (i.e. NatSemi, etc), and it's on a card, you can
"overclock" it by a factor of 2 or 4 to give 230,400 or 460,800 bits per
second. This essentially is a crystal replacement with a soldering iron.
Not hard but not for beginners. FreeBSD still thinks that the port is
115,200, you have just changed the underlying hardware to rev up the true
speed. I've done this. The interrupt load on the machine jumps accordingly
but it works. At 230,400 you will probably be seeing close to 2000
interrupts per second, because the 16550 doesn't have a real large FIFO.
I had minor problems with lossage on a 386DX/40.
Hayes ("Hayes Microcomputer Products") has something called an "ESP
Communications Accelerator". This is essentially a smart serial card which
has a much larger FIFO (1K), and has a switchable speed multiplier, so you
can get 230,400, 460,800, or 921,600 bps without soldering. Support for the
card is at least partially there in -current, although someone said they
weren't sure if the FIFO was fully enabled. This is a more pricey
alternative (list $99) but Hayes has a special right now, see
http://www.hayes.com/esp.htm
The Hayes solution is probably the best solution in the long run.
... Joe
-------------------------------------------------------------------------------
Joe Greco - Systems Administrator jgreco@ns.sol.net
Solaria Public Access UNIX - Milwaukee, WI 414/546-7968
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