Re: 6502/6510 ROM selection daughterboard

On 2012-06-03, at 12:32, Marko Mäkelä wrote:

>>> I wrote something like this in the Vic Flash Plugin.
>>
>> How did you deal with the need for VIC to "see" CHAROM on the  
>> daughterboard?
>
> I did not. The Vic Flash Plugin is similar to what you are looking  
> for, but not exactly the same. It only expands the memory, does not  
> replace any of the internal memory. The KERNAL, CHAROM and BASIC and  
> the internal RAM remain the same.

I see.

> Above, I was thinking a daughterboard that would be installed in the  
> 6510 socket. But, I think that it might be possible to implement a  
> KERNAL&BASIC replacement cartridge for the C64. As noted earlier  
> this week, you cannot directly observe writes to the 6510 on-chip I/ 
> O register at 0 and 1. But, maybe you could observe the state of the  
> 3 bank switching lines by observing the address lines and the CS  
> signals on the cartridge port. Then, by actively controlling the - 
> GAME or -EXROM lines on the 6510 half of the AEC, you could  
> effectively replace the internal ROMs with the cartridge ROM.
>
> This approach would require some careful studying of the PLA truth  
> table, and there might be some glitches.

Running KERNAL out of Cartridge has already been implemented in  
EasyFlash cart. I am not sure how this is done there (anyone checked  
that?) but it seem to work, including the RAM under KERNAL. I believe  
the same or similar approach could be used. Since we are to handle  
only two non-volatile bits (unlike tape stuff), it should be possible  
to tap on writes for example, as you noticed.

> I am not sure that the CHAROM could be replaced in this way. I don't  
> think it can be replaced with a 6510 daughterboard either, at least  
> not without redirecting some PLA lines.

I am aware that just plugging in the daughterboard is not going to be  
enough. That was the reason for my question about the way (I thought)  
you did it. I take additional lines need to be fed to the board in  
order to present CHAROM data to VIC whenever VIC expects it.

>> Now to the second part - both of you Ruud and Marko got the idea  
>> and know right away how to do it from the technical POV but this is  
>> also the point where I don't feel like I could do it myself. At  
>> least not in a reasonable time. Therefore if someone would be  
>> willing to make it according to my specs, I am ready not only to  
>> buy it right away but alternatively I can also fund some  
>> development / return costs, ...
>>
>> And of course the eternal hall of fame awaits for those who  
>> dare.. :-)
>
> Good luck. :-) I am too busy with my day job at the moment. Even in  
> a less busy period, it feels like a professional software developer  
> cannot work on software in spare time. Things were much easier when  
> I was a researcher, writing software only as part of my job. I feel  
> a bit quilty about this too, because I would like to teach  
> programming to my kids.  Somehow I just lack the power, do not have  
> much capacity to learn something new.

I understand. I was more about the hardware part, CPLD and Co..  
(although it may be hard to distinguish whether it's more hard or  
software ;-)  6502 software I should be able to take on myself.

-- 
SD!
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