Re: [cc65] Disable KERNAL ROM ?

From: <>
Date: 2013-02-13 16:10:19
On 2013-02-13, at 15:00, Oliver Schmidt wrote:

>>> I understand that the C64 would additionally require the setup of an
>>> IRQ thunk handler...
>> I am not 100% sure if I understand but IRQ and NMI vectors are on the top of KERNAL ROM. If this is banked out at least NMI should be covered but IRQ preferably as well. This can be done by placing appropriate values in the RAM but the values have to be "appropriate" as original ones point to ROM locations.
> The vectors in RAM have to point to routines that switch to ROM, call
> the original handler, switch back to RAM and return from the
> interrupt.

The original handlers may do RTI by themselves. This has to be taken care of properly. Presumably by stack tweaking.
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Received on Wed Feb 13 16:15:57 2013

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