Re: BASIC and System ROM replacements

From: Michał Pleban <*lists_at_michau.name*> Date: Sat, 25 May 2013 23:30:36 +0200 Message-ID: <51A12D7C.3080204@michau.name> · lists_at_michau.name

Hello!

Jim Brain wrote:

> Not to take this too far off topic, but I would be interested in an idea
> that would allow the ROM areas to be "banked" in such a way that you
> could fit 16kB of KERNAL or BASIC into a 8kB space.  I know the trivial
> is to use a "secret" location, but that's too simplistic.  I was
> thinking of something where a sequence of address accesses would trip
> the bank, and then if there was an IRQ when in the wrong bank, any
> access to the normal locations would "trip" it back by writing to a
> single location.  That way, accesses to ROM routines would incur no more
> than a few cycles to flip back to the correct bank.

How would you like to return to the previous ROM bank upon exit from the
interrupt handler? You can't detect a RTI instruction because the 6510
doesn't have the SYNC pin.

Regards,
Michau.

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