Hmm... Would this fire an IRQ every scanline, using the MMC3 mapper's IRQ function?

Init:
lda #$ff 'Fire IRQ after 1 scanline (mmc3 increments its counter, and fires IRQ when it hits $00
sta $c000 'Enable MMC3 IRQs
...

irq:
;Palette switch code
...
;Re-load IRQ timer
lda #$ff 'Fire IRQ after 1 scanline (mmc3 increments its counter, and fires IRQ when it hits $00
sta $c000 'Enable MMC3 IRQs
rti