[Coco] Mark McDougall's CoCo 1/2 FPGA Project

[Mark McDougall]

On 15/11/2017 2:03 PM, Barry Nelson wrote:

> You mean like this: 
> $6.62 SD to IDE adapter.
> Looks pretty “functional” to me… These adapter are quite common and readily available.

You're right, it is cool in its own right.

But not really suited for the task at hand. I developed my Coco1/2 
emulation on a proprietary FPGA board that had a CF card connector. Why? 
because CF was (is?) much easier to deal with, already interfaces to 
plenty of legacy computers including the Coco (GlenSide IDE/SuperIDE), 
and requires simply dropping in the base OCIDE core and little else.

I then ported the design to the TerASIC DE1, which has an SD card 
instead of CF. Since I wanted to support the "stock" DE1, I started on 
an 'IDE emulator' back-end that would allow me to simply selectively add 
support for SD without changing the Coco core or interface, allowing 
support for a slew of targets with either CF or SD.

Back in 2010 my colleague wrote the (read-only) SD interface - which, 
incidentally, doesn't use the then-more-commonly-used SPI mode - 
explicitly for this purpose. I wrapped another layer around this so it 
looked like an IDE device. It wouldn't take a lot of work to go back now 
and add write support to the SD interface, so that the Coco could write 
to an SD card like an IDE device. As I said, I just never got around to 
doing it.

One issue was the IDENTIFY-DEVICE command that needs to be supported, 
which returns the device geometry. This had to be configured on a 
case-by-case basis for whatever capacity SD card was being used with the 
Coco emulation and of course also required the appropriate configuration 
of HDBDOS used.

I wonder how the above-mentioned adapter handles IDENTIFY-DEVICE???

Regards,

-- 
Mark McDougall
<http://retroports.blogspot.com.au>