Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site utcsrgv.UUCP
Path: utzoo!utcsrgv!mason
From: mason@utcsrgv.UUCP (Dave Mason)
Newsgroups: net.micro.6809
Subject: Re: Radio Shack Floppy Disk Interface
Message-ID: <3021@utcsrgv.UUCP>
Date: Mon, 2-Jan-84 11:58:46 EST
Article-I.D.: utcsrgv.3021
Posted: Mon Jan  2 11:58:46 1984
Date-Received: Mon, 2-Jan-84 12:24:59 EST
References: <428@bbncca.ARPA>
Organization: University of Toronto/Ryerson Polytechnic Institute
Lines: 16

Thanks to Steve Dyer for the info about how the Disk controller works.
This is not a unique approach.  I have an S-100 system with a Versafloppy II
disk controller.  To read/write with this, every time you reference the
data register, the controller inserts wait states until the data is actually
available.
By my calculations, there is about 22 usec per byte (for a 8" DD floppy), so
I very much doubt that any useful work could be done and still service the
interrupts on time.  The standard solution to this is to store the sector
in a hardware buffer & copy the whole thing when available, saving on the
order of about 20 usec/byte, which adds up to significant wasted time in
the transfer of a complete sector.  Obviously this would increase the
cost of the disk controller more than the Radio Shack marketers would accept.
-- 
 -- Dave Mason, U. Toronto CSRG,
	{utzoo,linus,cornell,watmath,ihnp4,allegra,floyd,decwrl,
	 decvax,uw-beaver,ubc-vision}!utcsrgv!mason