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From: Robert Roland on 16 Apr 2010 09:06
On Fri, 16 Apr 2010 11:16:36 +0000 (UTC), Martijn van Buul
<pino(a)dohd.org> wrote:

>ISTR that the standard IRQ routine assumes I/O is mapped in, though; if
>RAM is mapped in instead you'll be facing problems first time an interrupt
>hits.

Good point. I only ever used this trick in the BASIC area, which
probably does not contain any I/O at all.
--
RoRo
From: commodorejohn on 16 Apr 2010 09:09
On Apr 16, 6:16 am, Martijn van Buul <p...(a)dohd.org> wrote:
> ISTR that the standard IRQ routine assumes I/O is mapped in, though; if
> RAM is mapped in instead you'll be facing problems first time an interrupt
> hits.
Correct; you'd have to disable interrupts when accessing the RAM, or
set up an interrupt-service routine of your own underneath the ROM.
For my purposes, I'm just going with the former; I plan to use this
memory for some constant graphics data, since the VIC-II can see the
RAM without it needing to be switched in. Load it up once and it's
good to go for the rest of the program's duration.
From: David Murray on 16 Apr 2010 17:11
It still amazes me how complex the memory is on the C64. That is
definitely one of the reasons I like the Plus/4 setup, despite is
other limitations.
From: commodorejohn on 16 Apr 2010 17:38
On Apr 16, 4:11 pm, David Murray <adri...(a)yahoo.com> wrote:
> It still amazes me how complex the memory is on the C64. That is
> definitely one of the reasons I like the Plus/4 setup, despite is
> other limitations.
Eh, the 64 isn't terribly complicated; it's only the $D000-DFFF area
that's all that confusing. Much weirder to work with are systems like
the Super Nintendo, where segments of memory are spread across only
certain ranges in the address space.
From: Anssi Saari on 16 Apr 2010 19:33
commodorejohn <commodorejohn(a)gmail.com> writes:

> Okay, this has been bugging me for a while. Is it possible to access
> the RAM that's underneath the character ROM and register area at $D000-
> DFFF?

Well, you got your answer, but I also remember wondering how this is
done back in the 80s. Some programs were so large they went under the
I/O-region. If you just do that normally, you get trouble as I recall.
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