Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!uunet!crdgw1!sixhub!davidsen
From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.unix.sysv386
Subject: Re: Son of FAS?
Message-ID: <3821@sixhub.UUCP>
Date: 1 May 91 03:20:03 GMT
References: <1991Apr25.010758.1522@pegasus.com> <1991Apr25.122805.1708@virtech.uucp>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 42

In article <1991Apr25.122805.1708@virtech.uucp> cpcahil@virtech.uucp (Conor P. Cahill) writes:

| There are several problems with polling.
| 
| The first problem is that the fifo's probably aren't big enough to handle 
| polling.  Polling is limited to 1 query every kernel clock cycle which
| is normally 100 (HZ) in the sysv386 world.  


| Another problem is that unless the port could be configured with
| some form of intelligence, the response to various events (drop of 
| cts, XOFF, etc) would be delayed.

  Your first point is fine, but who cares if it takes 10ms to recycle
after a call terminates. The cts probably dropped a second after the
carrier, so you will never know.

  Now, on the XOFF, any system with a FIFO may well keep right on
sending after the XOFF, and I think there's a standard which calls for
XOFF 1 sec before buffer full, I just can't remember where I saw it. We
hit this in 1978 or so when running a mainframe into an old S100 system
at 38.4.

| >Since most smart cards gain mostly from the reduced interrupt load they
| >place on the system wouldn't this blur the difference a bit more?
| 
| They can only do this cleanly when they have both fifo space and intelligence
| on the cards.

  The one real advantage to a really smart card is that you can have an
interrupt on every character, and allow XOFF to stop output in one
character time, etc. Note that even an 8250 has a one byte FIFO, so you
have a character in the shift register going out, and another in the
latch, committed to going out. So you can't easily stop in less than two
characters no matter what card you have (it can be done after one with
hardware).

-- 
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