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feat: implement Hblank and Vcount Interrupts 

Also implemented unique behaviour when writing to IF
This commit is contained in:
Rekai Nyangadzayi Musuka 2022-02-20 18:40:22 -05:00
parent e5ab8b51a9
commit c2cf2d2965
3 changed files with 67 additions and 14 deletions
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2
src/bus/io.zig
View File

@ -105,7 +105,7 @@ pub fn write16(bus: *Bus, addr: u32, halfword: u16) void {
0x0400_001C => bus.ppu.bg[3].hofs.raw = halfword,
0x0400_001E => bus.ppu.bg[3].vofs.raw = halfword,
0x0400_0200 => bus.io.ie.raw = halfword,
0x0400_0202 => bus.io.irq.raw = halfword,
0x0400_0202 => bus.io.irq.raw &= ~halfword,
0x0400_0208 => bus.io.ime = halfword & 1 == 1,
else => std.debug.panic("Tried to write 0x{X:0>4} to 0x{X:0>8}", .{ halfword, addr }),
}

36
src/cpu.zig
View File

@ -246,14 +246,8 @@ pub const Arm7tdmi = struct {
}
pub fn step(self: *Self) u64 {
if (self.bus.io.is_halted) {
// const ie = self.bus.io.ie.raw;
// const irq = self.bus.io.irq.raw;
// if (ie & irq != 0) self.bus.io.is_halted = false;
// log.warn("FIXME: Enable GBA HALTing", .{});
}
// If we're halted, the cpu is disabled
if (self.bus.io.is_halted) return 1;
if (self.cpsr.t.read()) {
const opcode = self.thumbFetch();
@ -272,6 +266,32 @@ pub const Arm7tdmi = struct {
return 1;
}
pub fn handleInterrupt(self: *Self) void {
const should_handle = self.bus.io.ie.raw & self.bus.io.irq.raw;
if (should_handle != 0) {
self.bus.io.is_halted = false;
// log.info("An Interrupt was Fired!", .{});
// Either IME is not true or I in CPSR is true
// Don't handle interrupts
if (!self.bus.io.ime or self.cpsr.i.read()) return;
// log.info("An interrupt was Handled!", .{});
// TODO: Should this behave like Software Interrupts?
const r15 = self.r[15] + if (self.cpsr.t.read()) @as(u32, 2) else 4;
const cpsr = self.cpsr.raw;
self.changeMode(.Irq);
self.cpsr.t.write(false);
self.cpsr.i.write(true);
self.r[14] = r15;
self.spsr.raw = cpsr;
self.r[15] = 0x000_0018;
}
}
fn thumbFetch(self: *Self) u16 {
const halfword = self.bus.read16(self.r[15]);
self.r[15] += 2;

43
src/scheduler.zig
View File

@ -25,8 +25,11 @@ pub const Scheduler = struct {
self.queue.deinit();
}
pub fn handleEvent(self: *Self, _: *Arm7tdmi, bus: *Bus) void {
pub fn handleEvent(self: *Self, cpu: *Arm7tdmi, bus: *Bus) void {
const should_handle = if (self.queue.peek()) |e| self.tick >= e.tick else false;
const stat = &bus.ppu.dispstat;
const vcount = &bus.ppu.vcount;
const irq = &bus.io.irq;
if (should_handle) {
const event = self.queue.remove();
@ -38,19 +41,36 @@ pub const Scheduler = struct {
},
.HBlank => {
// The End of a Hblank (During Draw or Vblank)
const old_scanline = bus.ppu.vcount.scanline.read();
const old_scanline = vcount.scanline.read();
const scanline = (old_scanline + 1) % 228;
bus.ppu.vcount.scanline.write(scanline);
bus.ppu.dispstat.hblank.unset();
vcount.scanline.write(scanline);
stat.hblank.unset();
// Perform Vc == VcT check
const coincidence = scanline == stat.vcount_trigger.read();
stat.coincidence.write(coincidence);
if (coincidence and stat.vcount_irq.read()) {
irq.coincidence.set();
cpu.handleInterrupt();
}
if (scanline < 160) {
// Transitioning to another Draw
self.push(.Draw, self.tick + (240 * 4));
} else {
// Transitioning to a Vblank
if (scanline < 227) bus.ppu.dispstat.vblank.set() else bus.ppu.dispstat.vblank.unset();
if (scanline == 160) {
stat.vblank.set();
if (stat.vblank_irq.read()) {
irq.vblank.set();
cpu.handleInterrupt();
}
}
if (scanline == 227) stat.vblank.unset();
self.push(.VBlank, self.tick + (240 * 4));
}
},
@ -59,11 +79,24 @@ pub const Scheduler = struct {
bus.ppu.drawScanline();
// Transitioning to a Hblank
if (bus.ppu.dispstat.hblank_irq.read()) {
bus.io.irq.hblank.set();
cpu.handleInterrupt();
}
bus.ppu.dispstat.hblank.set();
self.push(.HBlank, self.tick + (68 * 4));
},
.VBlank => {
// The end of a Vblank
// Transitioning to a Hblank
if (bus.ppu.dispstat.hblank_irq.read()) {
bus.io.irq.hblank.set();
cpu.handleInterrupt();
}
bus.ppu.dispstat.hblank.set();
self.push(.HBlank, self.tick + (68 * 4));
},
}