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From: jbs@mit-eddie.MIT.EDU (Jeff Siegal)
Newsgroups: net.unix-wizards
Subject: Re: dz-11 on a VAX-11/750 at 19,200 baud.
Message-ID: <1231@mit-eddie.MIT.EDU>
Date: Sun, 9-Mar-86 04:11:55 EST
Article-I.D.: mit-eddi.1231
Posted: Sun Mar  9 04:11:55 1986
Date-Received: Mon, 10-Mar-86 20:18:17 EST
References: <1577@brl-smoke.ARPA> <6815@boring.UUCP>
Reply-To: jbs@eddie.UUCP (Jeff Siegal)
Organization: MIT EECS Dept.
Lines: 37

In article <6815@boring.UUCP> jack@mcvax.UUCP (Jack Jansen) writes:
>Well, in fact you should even be grateful if it runs at 9600 baud...
>The DZ is completely interrupt driven, which means that *every character*
>causes an interrupt. So, 8 lines at 19.2Kb can produce an awful
>amount of interrupts......

I am only attempting to run one line at 19.2Kb (mine).  Most of the
other lines are either connected to 1200b modems, or not used.  All of
the users access the machine via a network.

One terminal, at whatever speed, doesn't seem like that many interrupts.
Also, see below about interrupts.

>Whenever the VAX doesn't serve input interrupts in time, the input
>silo fills up with unprocessed characters, and eventually some
>characters will be dropped. There are two solutions:
>- Set speed to 4800 baud. You will also see the performance of
>  your machine jumping up, since it doesn't have to spend so much
>  time on interrupt handling anymore.

Again, since there is only one fast terminal on the VAX, this
shouldn't be necessary.  I have looked at the number of interrutps on
the system under normal loads, and it is actually quite reasonable.
In fact, since the machine is a little short on memory, there is often
quite a bit of free CPU time floating around. (we are getting more
memory soon)

>- Replace the DZ by something better, probably some DH-11 clone.
>  These things use DMA for output, so you get far less interrupts.

We would have done this quite a while ago, if it was necessary, but
(again) the system does very little terminal i/o.

Jeff Siegal - MIT EECS