[Color Computer][Coco] Tandy Hard Disk Controller

[Gene Heskett]

On Saturday 04 March 2006 19:44, Mark Marlette wrote:
>Gene,
>
>I would have to go pull the 500 page spec out again. You seem to be up
> on it.
>
Only by hazy memory these days Mark.

>Can you tell me how they are doing collision detection?

Look at the interfaces pin descriptions.  ISTR there was a slim 
discussion around how that worked in there.

>This is how SCSI works on the TC^3 Interface.......
>
>SCSI devices communicate with each other by sending data packets
>across a shared bus. The device uses a hardware handshake to acquire
>the bus--all other devices must be silent while another device uses
>the bus. Unlike Ethernet, the bus is not accessed using a collision
>detection mechanism. Instead, devices follow a stateful algorithm to
>acquire the bus. When idle, the bus is in a state, or phase, known as
>the bus-free phase. If a device wishes to access the bus, it enters
>an arbitration phase, but only if the bus was previously in the
>bus-free phase. Clearly, there exists the classic problem in mutual
>exclusion where two devices check the state of the bus, both finding
>it in the bus-free phase, and go into arbitration. In this situation,
>the device with the highest SCSI ID always wins.

Thats as I recall it too from reading on it nearly 20 years ago now.

>Maybe you are confused with collision detection and Ethernet??? Not
>the case in SCSI.
>
>Did you ever get your TC^3 running on your system after Boisy and I
>set it all up for you in a standard configuration?

Yes, but I've never been able to replace the boot image and make it work 
with one of mine on a different virtual disk.  I haven't tried to 
overwrite the one you put on it however.  That would have the feel of 
going out on a limb and then sawing it off behind me.  :-)

>Mark
>Cloud-9

-- 
Cheers, Gene
People having trouble with vz bouncing email to me should add the word
'online' between the 'verizon', and the dot which bypasses vz's
stupid bounce rules.  I do use spamassassin too. :-)
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2006 by Maurice Eugene Heskett, all rights reserved.