Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!saxony!dgil
From: dgil@pa.reuter.COM (Dave Gillett)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Tis a puzzlement
Message-ID: <317@saxony.pa.reuter.COM>
Date: 14 Aug 90 07:24:37 GMT
References: <1990Aug10.002428.16237@ddsw1.MCS.COM>
Organization: Reuter:file Inc  (A Reuter Company) Palo Alto, CA
Lines: 21

In <1990Aug10.002428.16237@ddsw1.MCS.COM> andyross@ddsw1.MCS.COM (Andrew Rossmann) writes:
>  I noticed that when I ran my
>INFOPLUS program, that COM1 (which is a Practical Peripherals 2400 baud
>internal modem) had a baud rate of 2! 
>  If I slow the computer down, the baud rate is 'stuck' at
>452 baud.

I don't know for sure how InfoPlus is deriving  these rates, but I'd hazard a
guess that it's toggling the DLAB (Divisor Latch Access Bit) in the UART and
reading the divisor from the registers.  Unfortunately, on machines with 80386
processors it is possible for the read--or half of the read--to occur before the
write that toggles DLAB takes effect, unless the code forces a flush of the 
processor's look-ahead buffer.  I suspect that InfoPlus may be using code that
was written before the 80386 appeared, and so may not handle this correctly.

It's not clear from the original post whether the modem actually fails to
operate, or whether the problem is limited to the anomalous baud rate display. 
If the latter, then I wouldn't worry about it, but if the former then there
may be a similar problem with the character I/O routines.  In that case, a
version fixed to work with 386 processors ought to be available by now....
                                          Dave