[Coco] Largest supported HDD size?

Brett Gordon beretta42 at gmail.com
Sun Dec 11 22:23:11 EST 2016

Correct.  IDE doesn't "halt" or interrupt the controller.


On Sun, Dec 11, 2016 at 9:59 PM, RETRO Innovations <go4retro at go4retro.com>

> On 12/1/2016 8:10 PM, Darren A wrote:
>> On Thu, Dec 1, 2016 at 6:47 PM, RETRO Innovations wrote:
>> Is there a page that describes "no-halt"?  I think I understand the
>>> concept, but clarity is great.
>>> The floppy disk controllers for the CoCo make use of the CPU's HALT line
>> as
>> a handshake control during floppy I/O.  Here is how the "Disk Basic
>> Unraveled" book describes it:
>> "Data transfer between the computer and the disk drives through the FDC is
>> accomplished through a series of hardware and software 'tricks'. The slow
>> clock speed of the Color Computer will not allow data to be transferred in
>> the 'normal' method of getting a byte from the computer, giving it to the
>> FDC and then performing status checks until the FDC is not busy. There is
>> just not enough time for this when operating at double density. Part of
>> the
>> Color Computer's solution is a hardware trick whereby the disk controller
>> board will allow the FDC to halt the 6809 while the FDC is storing or
>> retrieving data. The halt flag will allow the DRQ signal from the FDC to
>> halt the 6809 so that the 6809 will wait while the FDC is processing a
>> data
>> request. This trick will allow the 6809 to pass data to the FDC as fast as
>> the FDC can take it by executing a fast loop of: grab a byte from RAM,
>> give
>> it to the FDC and loop back to get another byte. The analogous loop for
>> getting data will also work."
>> In reality, the 6809 at 0.89 Mhz is quite capable of running a polling
>> loop
>> to handle double-density data transfers with the FDC.  If the designer(s)
>> of the CoCo floppy controller had provided a way for software to read the
>> DRQ signal (other than from the FDC Status register), there would have
>> been
>> no need for the HALT trick.
>> - Darren
> That makes sense (as far as it explains things to me), but does the IDE
> interfaces have such a construct?  I don't see any such logic in the
> Glenside IDE, so they would all be no-halt, correct?
> Jim
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