Re: Commodore 64 Ultimate Cartridge project

On Monday 07 May 2012, you wrote:
> Hi,
> 
> On Mon, May 07, 2012 at 06:25:29PM +0200, Michał Pleban wrote:
> > >I also thought about it, since I've started to play with interfacing
> > >with SD card on SPI bus, currently only through PC parallel port (to
> > >"play" with it and some studies for myself), but I'd use a
> > >microcontroller with dedicated SPI capability (btw, I also thought
> > >about using ECN28J60 which is a 28-pin SPDIP ethernet controller with
> > >SPI bus - it's really cheap, and not so slow, even 20MHz SPI connection
> > >is OK for it -, maybe easier to play with it for a hobby user like me,
> > >without heavy SMD, etc soldering and PCB designing capaibilities).  One
> > >question came into my mind however: I would hate to use
> > 
> > >an EPROM just for bootstrap.  It would be interesting to see this works:
> > Well, I don't want to use any microcontroller for the simple reason
> > that 6502 is the only processor I know how to program :-P
> 
> I can understand you :) My only reason: interfacing with SPI bus is not so
> fast if some "bit banging" is used, and I wanted decent performance mainly
> because of the SPI based ethernet controller. However I am thinking on this
> still, as maybe serial shift register of the CIA can help here to speed
> things up a bit. In my idea uC is only needed to have some kind of fast
> SPI/serial converter (and also to "cache" some data inside the uC's memory
> still C64 is ready to process it, etc).
> 
> However as far as I can see, the goals are a "bit" different, you may not
> need this at all.

i would strongly advice not to use the 6510 for bitbanging - since that is 
dead slow. look at what speed the mmc64 can offer, it has a small spi 
controller with 8mhz spi clock (so one byte can be transfered each c64 cycle), 
and also uses a huge unrolled loop to read a sector from sd card. this is 
quite ok speed, but already on the slowish side of things. with bitbanging it 
would be at least 10 times slower, if not more - and unrolling loops would be 
out of the question because codesize would explode.

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