Path: utzoo!attcan!uunet!lll-winken!ames!netsys!ziggy!scotty
From: scotty@ziggy.UUCP (Scott Drysdale)
Newsgroups: comp.sys.amiga
Subject: Re: Multiple Serial Ports (Re: vt100 v2.9)
Message-ID: <157@ziggy.UUCP>
Date: 17 Jan 89 00:37:38 GMT
References: <8812150227.AA09671@postgres.Berkeley.EDU> <14049@oberon.USC.EDU> <554@sunkisd.CS.Concordia.CA> <3241@sugar.uu.net> <147@ziggy.UUCP> <373@madnix.UUCP> <150@ziggy.UUCP> <385@madnix.UUCP> <154@ziggy.UUCP> <393@madnix.UUCP>
Reply-To: scotty@ziggy.UUCP (Scott Drysdale)
Organization: Un*x Link,Frederick Md.
Lines: 27

In article <393@madnix.UUCP> aaron@madnix.UUCP (Aaron Avery) writes:
>The Z8530 has DMA block transfer support built in. For single byte reads
>(perhaps the norm), you set the block length to 1, and the byte will be
>stuffed into main memory and you will get an interrupt from the SCC. When

the 8530 does NOT support block DMA - it makes requests one byte at a time,
just like it would when interrupting.  any block length for DMA must be handled
by the DMA controller or otherwise detected.  it would seem that getting
an interrupt in addition to having the byte arrive via DMA isn't any better
than the interrupt driven method, anyways, except for transmitting if the
DMA controller knows about block lengths.
interrupts may be fine for a few ports (such as your twin-x thing) but for
high speed (19.2K or higher) operation without glitches, running multiple
ports, i think the board needs some brains of it's own.  consider that many
people have difficulty with the standard serial port at 9600 baud, which is
interrupt driven.  (yeah, i know, the internal serial port has zero recieve
buffering - so maybe 9600 is safe).

>
>-- 
>Aaron Avery, ASDG Inc.         "A mime is a terrible thing to waste."
>                                                             -- Robin Williams
>UUCP: {harvard|rutgers|ucbvax}!uwvax!nicmad!madnix!aaron
>ARPA: madnix!aaron@cs.wisc.edu


  --Scotty