[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
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.