zba/src/scheduler.zig

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const std = @import("std");
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const Bus = @import("Bus.zig");
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const Arm7tdmi = @import("cpu.zig").Arm7tdmi;
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const Order = std.math.Order;
const PriorityQueue = std.PriorityQueue;
const Allocator = std.mem.Allocator;
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const log = std.log.scoped(.Scheduler);
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pub const Scheduler = struct {
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const Self = @This();
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tick: u64,
queue: PriorityQueue(Event, void, lessThan),
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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));
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return sched;
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}
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pub fn deinit(self: Self) void {
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self.queue.deinit();
}
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pub fn handleEvent(self: *Self, _: *Arm7tdmi, bus: *Bus) void {
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const should_handle = if (self.queue.peek()) |e| self.tick >= e.tick else false;
if (should_handle) {
const event = self.queue.remove();
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// log.debug("Handle {} @ tick = {}", .{ event.kind, self.tick });
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switch (event.kind) {
.HeatDeath => {
std.debug.panic("[Scheduler] Somehow, a u64 overflowed", .{});
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},
.HBlank => {
// The End of a Hblank (During Draw or Vblank)
const old_scanline = bus.ppu.vcount.scanline.read();
const scanline = (old_scanline + 1) % 228;
bus.ppu.vcount.scanline.write(scanline);
bus.ppu.dispstat.hblank.unset();
if (scanline < 160) {
// Transitioning to another Draw
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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();
self.push(.VBlank, self.tick + (240 * 4));
}
},
.Draw => {
// The end of a Draw
bus.ppu.drawScanline();
// Transitioning to a Hblank
bus.ppu.dispstat.hblank.set();
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self.push(.HBlank, self.tick + (68 * 4));
},
.VBlank => {
// The end of a Vblank
self.push(.HBlank, self.tick + (68 * 4));
},
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}
}
}
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pub fn push(self: *Self, kind: EventKind, end: u64) void {
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self.queue.add(.{ .kind = kind, .tick = end }) catch unreachable;
}
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pub fn nextTimestamp(self: *Self) u64 {
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if (self.queue.peek()) |e| {
return e.tick;
} else unreachable;
}
};
pub const Event = struct {
kind: EventKind,
tick: u64,
};
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fn lessThan(_: void, a: Event, b: Event) Order {
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return std.math.order(a.tick, b.tick);
}
pub const EventKind = enum {
HeatDeath,
HBlank,
VBlank,
Draw,
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};