Re: userport: C64, Plus4, others?

From: Jim Brain <>
Date: Fri, 09 Mar 2012 22:38:00 -0600
Message-ID: <>
On 3/9/2012 3:52 PM, Gábor Lénárt wrote:
> Well, yes that's the uC part which is even more "alien" for me :) For 
> example I am not sure an average uC (like what you mentioned above) 
> has enough speed to serve an interrupt triggered by eg the PC (low 
> level active, afaik, but maybe it should be triggerd by the falling 
> edge instead?) line from C64; since I plan to use interrupts on the uC 
> part, so the uC itself can do other things meanwhile in the "main 
> program" (not in interrupt handler). Anyway, never mind, I will also 
> ask my "uC expert friend here" before I write too much non-senses here 
> :) It's really interesting on the DTV though where I guess even 
> 1Mbyte/sec is possible with DTV's DMA but then anyway since lack of 
> the handshaking, no interrupt service is needed but some kind of very 
> exact timing instead (or using somewhat slower "manual" method to 
> "ack" every bytes). 
AVR's can be triggered on rise, fall, high level, or low level.

I think, for now, ignore DMA.  As you note, you'll need some way to 
sync, which complicates things.

If you don't use DMA, you have more time to process a read/write (unless 
you're running a SuperCPU or Chameleon whic can issue IO at 1MHz)

> Well, I'm more used to have von Neumann architecture rather than Harvard :)
> Isn't it possible to use normal RAM for code with eg an AVR (maybe even
> internal RAM, I guess it's possible to use external RAM with uCs with
> external bus interface but it implies a rather pin-monster being, hehe)?
THere are some that can do that, but not the AVR.  As far as I know, PIC 
and AVR must run apps from FLASH, not RAM.
> So the flash would only contain the boot loader itself. But anyway a simple
> theory: I can store eg a word in my firmware which mean some kind of
> "version number". The boot loader can check the version number from the SD
> card and the version number flashed by the boot last time. If they are the
> same, no re-flashing is needed. Or maybe even some kind of checksumming
> which is more accurate stuff. Other possibility is to have a simple button
> I have to hold while powering-on the require loading (and flashing into the
> uC) a new firmware.

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Received on 2012-03-10 05:00:05

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