Posted By
Stinaris
on 2020-12-01
09:49:40
 |  Re: Cartridge and raster interrupts
Thanks Mad,
I spent sometime just seeing what was causing the issue.
Now I suspect, although not being an expert I am probably wrong.
So I have a bit of code in the cartridge that writes a little message. This works fine.
As well as that I try to set up a raster interrupt. Part of setting the vectors is doing an sta $ff3f
Which I think will tell the system not to look at the ROM version of the interrupt and look in RAM. What I suspect is when I do this it's switching to the RAM under $8000 (which doesn't exist on the C16).
However if I remove this line the program runs senza raster.
I'll try moving the raster code into ram and trying again. But for now I have to work.
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Ok so during my lunch break I had a quick play.
I copied the raster interrupt code to colourmap at $0800.
Set the raster interrupt to point to this.
Kept the cartridge code simple the following was observed.
With the "sta $ff3f" included, the raster interrupt to change the border colour works but the Cartridge code is never started.
Removing the "sta $ff3f" the cartridge code is run but the raster interrupt is never run.
It seems moving between RAM and ROM code is quite tricky.
So I got my cartridge code to run then at the end of the cartridge code I placed a "STA $ff3f" and the interrupt started albeit not consistently.It takes a few resets for it to settle. However the cartridge code no longer executes, because I presume there is no code where the PC currently references.
More investigation this evening.
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