Re: Patching in a CBM disk drive connection in a C64 case.

On 3/30/2022 1:21 PM, Claudio Sánchez - Tokafondo wrote:
> Thanks for all that explanation. I really appreciate it.
>
> What about keeping standard KERNAL routines along with new ones that 
> would use that DMA transfer mode?
You absolutely can, though the farther away from stock the routines get, 
the more likely you'll need to include a copy of the stock KERNAL you 
can switch in for those apps/demos/etc. that just cannot handle the new 
routines and refuse to run in the modified KERNAL for some reason 
(internal subroutine addresses moved, etc.)
>
> If compatibility is a must, then that could be a way.
It's not a must per se, I was just pointing out how things might break 
if you switched any of the routines and that you can't speed up the 
transfer without changing the routines (or the hypervisor idea)
>
> I understand the necessity of having old software running in new 
> formats, but at some point the CBM machines would be able to get 
> advantage of faster speeds and bigger capacities even breaking 
> compatibility.

Let me share a true story.

CBM Disk drives and media are bulky, prone to issues, and hard to 
transfer files onto.

At some point, the 1541-III was developed, which begat sd2iec. Both as 
SD-based drive emulators.

The sd2iec firmware was not 100% compatible with the 1541, but did offer 
lots of DOS-level compatibility, and even added in a fair number of 
features from CMD's FDD and HDD line.  It was also positioned as a cheap 
option, as one could construct from parts for USD $20 or so, and 
purchase for $50.00 or so.

The idea was the most of the games and such were "cracked" and could be 
loaded with JiffyDOS or similar.

The firmware even understands a few of the more popular speeder routines.

As well, it was never advertised (at least by the developer) as a 1541 
replacement.

But, go online and look at the comments for the sd2iec devices. They get 
bashed all the time.

Moral: Even though most people will have good luck with a less than 100% 
compatible device like sd2iec, there's a whole crowd of people out there 
who will not only not accept a solution that's < 100% compatible, they 
will actively discourage others from owning or using it and will take 
every opportunity to disparage the device itself.

Jim

-- 
Jim Brain
brain_at_jbrain.com
www.jbrain.com