feat: initial ACPI support

src/platform/acpi/hpet.zig

@@ -0,0 +1,40 @@
+const b = @import("base");
+const std = @import("std");
+const acpi = b.pl.acpi;
+const mm = b.mm;
+const ke = b.ke;
+
+var hpet_timer: ke.TimeCounter = .{
+    .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 {
+    hpet_regs = @ptrFromInt(mm.p2v(hpet.base_address.address));
+
+    hpet_timer.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.time.register_source(&hpet_timer);
+}
+
+fn read_hpet() u64 {
+    return b.mmio_read(u64, @intFromPtr(&hpet_regs.main_counter_value));
+}