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From: altman@sbgrad12.cs.sunysb.edu (Jeff Altman)
Newsgroups: comp.windows.ms
Subject: Re: Win 3.0 & high speed modem use
Keywords: uart,hst,frontdoor
Message-ID: <1990Jul24.140211.23811@sbcs.sunysb.edu>
Date: 24 Jul 90 14:02:11 GMT
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I tried to respond directly to this thread but the response bounced.

BAsicly, the trick to running high speed trnasfers with Windows
is to play with the PIF file and the SYSTEM.INI file.

This only applies to Enhanced mode as there is no multitasking of 
DOS Telecommunication packages under real or standard modes.

First, in the PIF file, memory for the Comm App must remain locked.

Second, in the SYSTEM.INI file (described in SYSINI2.TXT) there
are a number of settings which should be added.

COMBoostTime
COM?Buffer
COM?Protocol

These lines control the behavior of DOS Comm Apps under Windows.
Win3 acts as the interrupt handler for the UART.  When a character
is received, Win3 places it into a buffer until the DOS Comm App
is active.  The default for Win3 is 128 characters.  However, at 
high speed this 128 characters goes real fast.  I set mine at 1024
however even higher values will improve performance.

The COM?Protocol is handy if your Comm package is using XON-XOFF
for flow control.  When the Comm Package is active, Win3 starts to
dump the Comm Buffer to the Interrupt handler for the ComM PAckage.
Not all PAckages can handle the speed at which data flows in and 
some characters will be lost.  If the Protocol is set to XOFF then
when the Comm Package sends an XOFF Win3 will stop dumping the 
buffer.  This reduces character loss.

The final item to change (only if necessary) is the COMBoostTime.
This specifies the minimum number of milliseconds which should
be given to the Comm Package in order to process the incoming data.
It defaults to 2 milliseconds, and higher numbers will improve 
performance of the Comm PAckage but will have a high impact on
other applications (both DOS and Win3) which are simultaneously 
running.

I have used these techniques to successfully perform Kermit file
transfers at 19200 via a ROLM PBX (100% clean connection).  One
tip for Kermit users, the TIMER should be shut off on the side
running under Win3.  The Kermit Protocol states that after the 
start of a packet is received there can not be more than about 
1 second between characters.  This is sometimes a problem because
of the intermediate buffering.  Shutting the timer off does not cause
any problems.  

- Jeff (jaltman@ccmail.sunysb.edu)