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From: d9mikael@dtek.chalmers.se (Mikael Wahlgren)
Newsgroups: comp.os.os2.misc
Subject: Re: Serial port and 16550 chip
Message-ID: <1991May31.202957.5491@mathrt0.math.chalmers.se>
Date: 31 May 91 20:29:57 GMT
References: <13262@uhccux.uhcc.Hawaii.Edu>
Sender: news@mathrt0.math.chalmers.se (Evald Nyhetsson)
Organization: Chalmers University of Technology, Gothenburg, Sweden
Lines: 23

In article <13262@uhccux.uhcc.Hawaii.Edu> tholen@uhccux.uhcc.Hawaii.Edu (David Tholen) writes:

>The remaining question is this:  why doesn't the supplied driver support
>high baud rates?  IBM's hardware will support higher serial port speeds
>(at least the new Models 90 and 95), and the available communications
>programs will also support higher speeds, so why was the driver written to
>support speeds up to only 19200, especially if the patch is as simple as
>Mr. Wahlgren has indicated?  Is there a reliability problem?  Can some
>knowledgable IBMer explain why the higher speed shouldn't be used?

The current COM0x.SYS driver deliberately compares the given baud rate
with the maximum 19200 bauds, and jumps out with an error message if
the baud rate is too high.  This is easy to see in the patch message I
sent before (the first character is the OPcode for a compare instruction
and the following two characters the value 19200).

I think this is a conservative decision by IBM, as SOME of their machines
(especially those without 16550 UARTs) won't be able to utilize the high
speeds, while most others certainly will manage this, without any problems
(I have used the high speeds for quite some time, and doesn{t experience
any loss of characters or other symptoms).

Mikael Wahlgren      d9mikael@dtek.chalmers.se