Subject: Re: Serial port and 16550 chip
From: d9mikael@dtek.chalmers.se (Mikael Wahlgren)

>It is VERY easy to patch both COM01.SYS and COM02.SYS (OS/2 version 1.3)
>to support any speed up to maximum 115 kBaud.  Please write a mail if
>interested.  Because of the CPUI-load, I wouldn't recommend this patch
>to anyone without the 16550 FIFO though.

As I got a lot of mail requesting the patch, I will describe it here.  First
of all, I don't know about the legal matters implementing this patch, as you
have to alter device drivers from IBM, so you take all responsibility yourself.

Take a backup copy of your original COM0x.SYS driver before you implement
this patch.  Use a HEX-editor (like PC-TOOLS) and search in the COM01.SYS
or COM02.SYS driver for the HEX-string:

3D 00 4B

This string should only appear in one place, and you should replace it by the
string:

3D FF FF

This is all, and you only have to reboot with the patched COM0x.SYS driver.
Note that I promised a little too much before, as the API for setting baud
rate only accepts 16 bit baudrates, so the maximum baud rate you can use
is 65535 baud (I think the highest useable baudrate is 57600 bauds).  Also
note that your communication program has to support these speeds.  Many
programs just won't let you set the baudrate to anything higher than 19200
(or if you are lucky it will accept 38400).  M2Zmodem will accept any
baud rate up to 57600.

I have tested this patch with:

IBM OS/2 1.3 SE COM02.SYS (offset 6081 dec)
IBM OS/2 1.3 SE COM01.SYS (offset 3905 dec)
IBM OS/2 1.3 EE COM01.SYS (offset 3905 dec)
IBM OS/2 1.3 EE COM02.SYS (won't work, can't find string?)

If you have any further questions please mail me.

Mikael Wahlgren      d9mikael@dtek.chalmers.se