Re: C64/VIC Bus state during RESET

silverdr_at_wfmh.org.pl
Date: 2008-11-12 01:08:46

On 2008-11-11, at 23:03, silverdr@wfmh.org.pl wrote:

> 3. Sure, but 1) see above, and 2) isn't it much more fun to push  
> reset with a key combination [...]
> and choose one from the menu at will?!

Hm, that I guess would require somewhat different approach than what  
was written by Jim. It would have to blend itself in at top of the  
address space, release RESET and execute some target machine code  
before doing the second reset rather than "holding the machine in  
RESET state" but this is not impossible, right?

1. At RESET, the utility code is put over last pages and uses the 6502  
vectors for start, after checking and setting the flag for [4.]
2. It checks the ports for the key combo and upon finding presents the  
menu. Otherwise proceeds with default KERNAL.
3. the KERNAL image is selected and the utility code communicates with  
the uC (this possibility is supposed to be there anyway), sending it  
appropriate data about the choice and triggering the second phase

Now:

4. The second phase pulls RESET one more time (and while "holding the  
machine in RESET state" clears a flag or something so that it doesn't  
go back to [1.] and RESET endlessly nor skips the menu all the time)
5. Chosen KERNAL is blended-in and RESET is de-asserted.

Does that make sense at all?

Regards,

P.


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