119 lines
3.7 KiB
Zig
119 lines
3.7 KiB
Zig
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;
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const PriorityQueue = std.PriorityQueue;
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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,
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queue: PriorityQueue(Event, void, lessThan),
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pub fn init(alloc: Allocator) Self {
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var sched = Self{ .tick = 0, .queue = PriorityQueue(Event, void, lessThan).init(alloc, {}) };
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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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}
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pub inline fn now(self: *const Self) u64 {
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return self.tick;
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}
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pub fn handleEvent(self: *Self, cpu: *Arm7tdmi) void {
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if (self.queue.removeOrNull()) |event| {
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const late = self.tick - event.tick;
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switch (event.kind) {
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.HeatDeath => {
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log.err("u64 overflow. This *actually* should never happen.", .{});
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unreachable;
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},
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.Draw => {
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// The end of a VDraw
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cpu.bus.ppu.drawScanline();
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cpu.bus.ppu.handleHDrawEnd(cpu, late);
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},
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.TimerOverflow => |id| {
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switch (id) {
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0 => cpu.bus.tim[0].handleOverflow(cpu, late),
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1 => cpu.bus.tim[1].handleOverflow(cpu, late),
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2 => cpu.bus.tim[2].handleOverflow(cpu, late),
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3 => cpu.bus.tim[3].handleOverflow(cpu, late),
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}
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},
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.ApuChannel => |id| {
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switch (id) {
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0 => cpu.bus.apu.ch1.channelTimerOverflow(late),
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1 => cpu.bus.apu.ch2.channelTimerOverflow(late),
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2 => cpu.bus.apu.ch3.channelTimerOverflow(late),
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3 => cpu.bus.apu.ch4.channelTimerOverflow(late),
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}
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},
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.FrameSequencer => cpu.bus.apu.tickFrameSequencer(late),
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.SampleAudio => cpu.bus.apu.sampleAudio(late),
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.HBlank => cpu.bus.ppu.handleHBlankEnd(cpu, late), // The end of a HBlank
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.VBlank => cpu.bus.ppu.handleHDrawEnd(cpu, late), // The end of a VBlank
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}
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}
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}
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/// Removes the **first** scheduled event of type `needle`
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pub fn removeScheduledEvent(self: *Self, needle: EventKind) void {
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var it = self.queue.iterator();
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var i: usize = 0;
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while (it.next()) |event| : (i += 1) {
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if (std.meta.eql(event.kind, needle)) {
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// This invalidates the iterator
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_ = self.queue.removeIndex(i);
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// Since removing something from the PQ invalidates the iterator,
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// this implementation can safely only remove the first instance of
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// a Scheduled Event. Exit Early
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break;
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}
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}
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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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}
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pub fn nextTimestamp(self: *Self) u64 {
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if (self.queue.peek()) |e| return e.tick;
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unreachable; // There's always the HeatDeath event scheduled
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}
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};
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pub const Event = struct {
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kind: EventKind,
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tick: u64,
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};
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fn lessThan(_: void, a: Event, b: Event) Order {
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return std.math.order(a.tick, b.tick);
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}
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pub const EventKind = union(enum) {
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HeatDeath,
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HBlank,
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VBlank,
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Draw,
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TimerOverflow: u2,
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SampleAudio,
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FrameSequencer,
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ApuChannel: u2,
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};
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