Zag/src/platform/acpi/hpet.zig

const b = @import("root");
const std = @import("std");
const acpi = b.pl.acpi;
const mm = b.mm;
const ke = b.ke;

var hpet_cs: ke.ClockSource = .{
    .name = "HPET",
    .quality = 50,
    .frequency = 0, // Filled at runtime
    .read_count = read_hpet,
    .mask = std.math.maxInt(u64),
    .p = 0,
    .n = 0,
};

var hpet_regs: *volatile acpi.HpetRegs = undefined;

const femtos_per_s = 1_000_000_000_000_000;

pub fn init(hpet: *acpi.HpetTable) linksection(b.init) void {
    if (ke.clock.is_better_than(&hpet_cs)) return;

    hpet_regs = @ptrFromInt(mm.p2v(hpet.base_address.address));
    hpet_cs.frequency = femtos_per_s / (b.mmio_read(u64, @intFromPtr(&hpet_regs.general_capabilities)) >> 32);

    // Disable timer.
    b.mmio_write(u64, @intFromPtr(&hpet_regs.general_configuration), 0);

    // Reset counter.
    b.mmio_write(u64, @intFromPtr(&hpet_regs.main_counter_value), 0);

    // Enable timer.
    b.mmio_write(u64, @intFromPtr(&hpet_regs.general_configuration), 1);

    ke.clock.register_source(&hpet_cs);
}

fn read_hpet() u64 {
    return b.mmio_read(u64, @intFromPtr(&hpet_regs.main_counter_value));
}