Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!ames!ucbcad!ucbvax!CORY.BERKELEY.EDU!dillon
From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga
Subject: Re: Serial port expansion
Message-ID: <8801130337.AA27948@cory.Berkeley.EDU>
Date: 13 Jan 88 03:37:05 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 33


	I have been following this discussion loosly.  It seems clear that
programs should have a way of setting the serial.device name and unit number. 
(or any other device they use...)

	And as far as having yet another device that determines which serial
device is actually used, this is quite easy to do without any modification
to the operating system.  Simply name the device serial.device and poof,
it gets all OpenDevice() calls.  It can then open the *real* serial.device
(with some other name... maybe serial0-5.device, etc...) and then die.

	The latter having the advantage that it is completely compatible, does
not require programmers to provide specifiable device names, does not require
serial.device's to know about each other, allows logical assignment of unit
ranges, and works with all existing programs.

----
DMA suggestion:	It shouldn't be too hard to have a little piece of
logic to handle DMAing to/from main memory from a single chip microcomputer. 
All it takes is a little latching logic for the address and data and a two or
three state machine to handle the bus transfer.  The rest would be handled
by a single chip microcomputer.  At the relatively slow rates serial goes
compared to the bus bandwidth, this would be a low-cost, highly efficient 
solution.

	Example: an MC68705, some 6551's, a couple of flipflops and some
	HC374's.  Using the MC68705 means the RAM, EPROM, and IO are in the
	processor.  You might want to use an HC6303 or 6805 instead, which
	have RAM+timer+lessIO onboard but not ROM.  Or you could even use one
	of those Intel single chip IO processors though I haven't looked at
	their specs.

				-Matt