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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