const std = @import("std"); const Bus = @import("Bus.zig"); const Arm7tdmi = @import("cpu.zig").Arm7tdmi; const Order = std.math.Order; const PriorityQueue = std.PriorityQueue; const Allocator = std.mem.Allocator; const log = std.log.scoped(.Scheduler); pub const Scheduler = struct { const Self = @This(); tick: u64, queue: PriorityQueue(Event, void, lessThan), pub fn init(alloc: Allocator) Self { var sched = Self{ .tick = 0, .queue = PriorityQueue(Event, void, lessThan).init(alloc, {}) }; sched.push(.HeatDeath, std.math.maxInt(u64)); return sched; } pub fn deinit(self: Self) void { self.queue.deinit(); } 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(); // log.debug("Handle {} @ tick = {}", .{ event.kind, self.tick }); switch (event.kind) { .HeatDeath => { std.debug.panic("[Scheduler] Somehow, a u64 overflowed", .{}); }, .HBlank => { // The End of a Hblank (During Draw or Vblank) const old_scanline = vcount.scanline.read(); const scanline = (old_scanline + 1) % 228; 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 == 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)); } }, .Draw => { // The end of a Draw 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)); }, } } } pub fn push(self: *Self, kind: EventKind, end: u64) void { self.queue.add(.{ .kind = kind, .tick = end }) catch unreachable; } pub fn nextTimestamp(self: *Self) u64 { if (self.queue.peek()) |e| { return e.tick; } else unreachable; } }; pub const Event = struct { kind: EventKind, tick: u64, }; fn lessThan(_: void, a: Event, b: Event) Order { return std.math.order(a.tick, b.tick); } pub const EventKind = enum { HeatDeath, HBlank, VBlank, Draw, };