Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!rpi!crdgw1!sixhub!davidsen
From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.unix.sysv386
Subject: Re: Son of FAS?
Message-ID: <3823@sixhub.UUCP>
Date: 1 May 91 03:42:09 GMT
References: <1991Apr25.010758.1522@pegasus.com> <1991Apr26.013550.20175@netcom.COM> <1991Apr27.231847.8873@pcserver2.naitc.com>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 26

In article <1991Apr27.231847.8873@pcserver2.naitc.com> kdenning@pcserver2.naitc.com (Karl Denninger) writes:

| The Equinox drivers and newer Digiboard drivers on the host side use a
| derivitive of polling.  They use ADAPTIVE polling.  This takes advantage of
| the fact that you really can't tell the difference between a 50ms delay and
| no delay in reading characters from a serial port at low baud rates..... and
| the driver can "learn" the data rate and adjust it's polling rate.  Also,
| polling to check one bit is VERY fast (ie: is there anything in the buffer
| that I have to deal with right now).  You can do this from the clock
| interrupt with nearly no overhead.
| 
| Since the board has buffer memory on it, this works very well.  On each
| "tick" the board can be checked for pending input and output buffer
| availability.  If there is input pending or output buffer space (and you
| have output for the card) you can then set a flag for later -- and when you
| get around to it do the actual input and output in a batch.

  What kind of latency do they get on XOFF? Whats the worst case number
of characters or ms between the XOFF coming in and the output stopping?
The obvious answer is 10ms, or about 40 characters, but I hope that's
wrong, because it's too many.
-- 
bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me