MMC3 IRQ setup doesn't work "out of the box"

[Wendel Scardua]

On a MMC3 C++ project I was trying to use the irq-related API (based on nesdoug.h), and spent a long time trying to figure out why the irq wasn't "irqing", until someone pointed out to me that, if cli only happens inside nmi (like the first call to irq_parser possibly does, when the first instruction is a scanline counter), the flag state will be reverted by the nmi's rti. Which means that if the interrupts aren't enabled beforehand during initialization, they will never be.

For now I'm doing an asm volatile("cli") at the start of my main myself.

I think maybe either:

• interrupts should start enabled for MMC3, or
• if such magic is possible with llvm-mos, they should start enabled if irq functions are being used, or
• set_irq_ptr should enable it, or
• mapper.h should have a comment telling the user to enable it beforehand