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boomlinde • yesterday at 4:57 PM • 2 replies • view on HN

You can chain handlers by simply rewriting the interrupt vector. Something like this (for a sequence of two handlers):

    handler1
        ; ...
        lda #<handler2
        sta $fffe
        lda #>handler2
        sta $ffff
        lda #line2
        sta $d012
        rti

    handler2
        ; ...
        lda #<handler1
        sta $fffe
        lda #>handler1
        sta $ffff
        lda #line1
        sta $d012
        rti
To my intuition it seems it would be quicker, though slightly larger.

I've only skimmed through the article so maybe there's a reason the author considered this and opted not to. Running out of memory maybe?

Replies

neonz80 • yesterday at 10:24 PM

If you put both handlers in the same 256 byte page you can get away with only updating the low byte of the address.

classichasclass • yesterday at 7:46 PM

Nitpick: I think he still has the Kernal banked in, so he'll need to use the soft vector at $0314. But that is exactly how I've done chained raster splits otherwise. It's really the most straightforward approach.