[Coco] Re: Coco Digest, Vol 31, Issue 23

[Tony C]

Date: Mon, 06 Mar 2006 14:04:41 -0500
From: Gene Heskett <gene.heskett at verizon.net>
Subject: Re: [Coco] RE: Tandy Hard Disk Controller
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Message-ID: <200603061404.41194.gene.heskett at verizon.net>
Content-Type: text/plain; charset=us-ascii

On Monday 06 March 2006 09:46, Mark Marlette wrote:
>In all of my years of working with SCSI on the CoCo. I have NEVER seen
>a CoCo host adapter have a SCSI ID.
>
>For many reasons, it is not this simple.
>

>>Huh?  Should it not be address 7 on the old narrow buss?  How else could
>> the drive notify it when the data is ready if a disconnect has been
done?
Even before the drive could re-connect to send data, the host  has to First
arbitrate for control of the buss, win arbitration, then send the read
command  for which the drive was re-connecting to return the data for.

You are correct- disconnects don't make sense on the COCO and just add a
tiny bit of overhead to each transaction, if they are enabled by the host
(but it is more likely that they are not enabled). I doubt that OS9 was
sophisticated enough to be able to handle out-of-order command completion
from SCSI devices.