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8bitworkshop/presets/nes/irq.c

80 lines
1.8 KiB
C

// bank-switching configuration
#define NES_MAPPER 4 // Mapper 4 (MMC3)
#define NES_PRG_BANKS 4 // # of 16KB PRG banks
#define NES_CHR_BANKS 1 // # of 8KB CHR banks
#include <peekpoke.h>
#include <string.h>
#include <nes.h>
#include "neslib.h"
// link the pattern table into CHR ROM
//#link "chr_generic.s"
// "strobe" means "write any value"
#define STROBE(addr) __asm__ ("sta %w", addr)
#define MMC3_IRQ_SET_VALUE(n) POKE(0xc000, (n));
#define MMC3_IRQ_RELOAD() STROBE(0xc001)
#define MMC3_IRQ_DISABLE() STROBE(0xe000)
#define MMC3_IRQ_ENABLE() STROBE(0xe001)
void draw_text(word addr, const char* text) {
vram_adr(addr);
vram_write(text, strlen(text));
}
word counters[128];
byte irqcount = 0;
void __fastcall__ irq_nmi_callback(void) {
// check high bit of A to see if this is an IRQ
if (__A__ & 0x80) {
// it's an IRQ from the MMC3 mapper
// change PPU scroll registers
PPU.scroll = counters[irqcount & 0x7f] >> 8;
PPU.scroll = 0;
// advance to next scroll value
++irqcount;
// acknowledge interrupt
MMC3_IRQ_DISABLE();
MMC3_IRQ_ENABLE();
} else {
// this is a NMI
// reload IRQ counter
MMC3_IRQ_RELOAD();
// reset scroll counter
irqcount = 0;
}
}
void main(void)
{
// set up MMC3 IRQs every 8 scanlines
MMC3_IRQ_SET_VALUE(7);
MMC3_IRQ_RELOAD();
MMC3_IRQ_ENABLE();
// enable CPU IRQ
__asm__ ("cli");
// set IRQ callback
nmi_set_callback(irq_nmi_callback);
// set palette colors
pal_col(1,0x04);
pal_col(2,0x20);
pal_col(3,0x30);
// fill vram
vram_adr(NTADR_A(0,0));
vram_fill('A', 32*28);
// turn on PPU/interrupts
ppu_on_all();
// loop forever, updating each counter at a different rate
while(1) {
byte i;
for (i=0; i<128; i++) {
counters[i] += i*16;
}
ppu_wait_frame();
}
}