Path: utzoo!attcan!uunet!lll-winken!ames!xanth!nic.MR.NET!umn-d-ub!uwvax!astroatc!nicmad!madnix!aaron
From: aaron@madnix.UUCP (Aaron Avery)
Newsgroups: comp.sys.amiga
Subject: Re: Multiple Serial Ports (Re: vt100 v2.9)
Message-ID: <373@madnix.UUCP>
Date: 10 Jan 89 09:05:48 GMT
References: <8812150227.AA09671@postgres.Berkeley.EDU> <14049@oberon.USC.EDU> <554@sunkisd.CS.Concordia.CA> <3241@sugar.uu.net> <147@ziggy.UUCP>
Reply-To: aaron@madnix.UUCP (Aaron Avery)
Organization: ASDG Incorporated
Lines: 36

In article <147@ziggy.UUCP> scotty@ziggy.UUCP (Scott Drysdale) writes:
>first of all, anyone who develops a multiport serial board that doesn't have
>it's own CPU on board is absolutely nuts.  using interrupts from the UARTs
>is also grounds for the electric chair.  i've done this before - the board was

We've done this before, too. And I guess we're absolutely nuts and should be
put to death, too.

The real toss-up here is that if you want to design a high-end (pricey)
multiport serial board, you must choose between an on-board processor, and
DMA support.
With DMA, the main CPU doesn't have to move any data anywhere, thus data-
transfers are easier on it. Also, the main CPU gets about as many interrupts
either way - there's a bit more overhead for checking the ports to see who's
really done, and vectored interrupts would take care of that.
The main reason for putting a processor on-board is to add intelligence to it,
such as command parsing, built-in error correction protocols, etc.


>an intel SBC547, which is a multibus I card with and 80186, 4 zilog SCCs, and

Oh, and since I'm nuts, I guess I get to call anyone who programs an 80186 in
assembly nuts.

>anyone have any comments?

Yes. I like the idea of a timer interrupt for handling this if you don't have
DMA. The real problem with that is when you only have one CPU to handle the
interrupts, the timer is more overhead than needed when the ports _aren't_
very active.

-- 
Aaron Avery, ASDG Inc.         "A mime is a terrible thing to waste."
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