Friday, July 20, 2007

RR-Net and MMC cards

I've been playing with a cool little design for an MMC card reader on the C64, mainly so I can understand it and then try it out on the Plus/4. I've had to modify it a little as I dont have the chip he's using, but it should still work okay.

It's a user port based one so is easy to play with, but it did mean I couldn't use my download cable! Damn! However, now that I have an RR-NET, I found a cool little program called udpslave, which is exactly like my download program anyway, but over ethernet! Very neat. it also means you dont need a parallel port anymore, so I could use a laptop.

The more I look at these things the more I think it would be very cool to have on the Plus/4. Its another fairly simple addition I could add to the memory expansion I guess, as it only needs 4 bits of memory (3 out,1 in).

Its in situations like this though, that I'd KILL for a proper remote debugger! This is the reason you need to step through the actual code on the real machine...Oh well.. back to printing to the screen I guess.


TNT said...

Smart arse question: what's the going price for plus/4 these days. I might be buying some stuff from UK, and one +4 added in wouldn't make shipping much higher. I'd like to know if the price is right.

(No, I ain't telling anybody how much and where, nayh nayh!)

BTW, there's Serial Slave as well, I prefer C64 doing the master stuff and let the soulless PC be the slave ;)

Mike said...

Not sure really... ebay's a little wild just now, then should be fairly cheap (£15), but I've not seen any go for that reciently.

Yep, I've got a silver surfer as well :)

I didnt actually think it would have been much faster tha my parallel cable since the C64 copying bytes appeared to be the limiting factor, but it looks like its twice as quick - interesting.

TNT said...

Seems like plus/4 are bit scarce at the moment. I found one in the completed eBay listings for £21, and that was UK only auction.

You can do XModem at 115 kbps with SilverSurfer, if you want to go to 230 kbps you need to drop checksum and add some more throttling. I had to buy USB_to_RS232 converter to make my PC capable of that ;)

Mike said...

Was the C64 able to keep up with that? I didnt think it had the CPU power to even copy that number of bytes that quickly!

I have a couple of deads Plus4's here for spares, I might be able to make a working one, but you'd still need a +4 PSU, which is even harder to come by.

TNT said...

Yes, that was the reason for extra bytes when page changed. Loop inside page was something like "lda #1; bit ss_lsr; beq *-3; lda ss_rxd; sta (dest),y;iny;bne .loop" and then page change + read two or three bytes until you get something else than magic char, then back to loop.

I never got any CRC errors at 115 kbps so there is no checksumming.

The above can be made one cycle faster by using code in zero page (sta abs,y), but I haven't tested to see if it makes any difference.