[Coco] DCD's (Good Old) 68HC08 MCU Is Going Strong

[Mark McDougall]

On 10/04/2014 2:58 PM, Kip Koon wrote:

> I just don't know how to
> write the SD Memory Card interface code to use it for the primary online
> storage device.  Darren, could you help us with this since you have created
> the CocoSDC?

I doubt Darren can help as his design (IIUC) requires an external micro 
to handle the SD file formatting and communications.

If you're looking to emulate floppy drives with a FAT-formatted SD card 
then you're not going to have much luck. Decoding the FAT filesystem 
requires a processor and many of the existing FPGA emulations use 
external microcontrollers for exactly that purpose. Your other option is 
a small (2nd) soft-core processor in the FPGA itself with FatFS or 
similar to handle that side of things. Then you need to tack on a floppy 
controller emulation on the front end.

Emulating a hard disk on an SD card is easier; CF easier still. SD's SPI 
operation mode - whilst slower - is definitely fast enough for an 8-bit 
processor and can be implemented in a relatively simple state machine 
wrapped around an open SPI controller core, for example. Then use the 
opencores IDE controller on the front end.

Regards,

-- 
|              Mark McDougall              | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug> |   with less resistance!"