Calibrated timer / clock

src/tests.zig

@@ -49,6 +49,8 @@ pub fn run(case: []const u8, boot_info: *const BootInfo) void {
         smoke(boot_info);
     } else if (eql(case, "timer")) {
         timer();
+    } else if (eql(case, "clock")) {
+        clock();
     } else if (eql(case, "vmm")) {
         vmm();
     } else if (eql(case, "heap")) {
@@ -204,6 +206,27 @@ fn heapTest() void {
     result();
 }
 
+/// Verify the calibrated clock: a plausible measured LAPIC frequency, the
+/// configured tick rate, and monotonic uptime that advances with real ticks.
+fn clock() void {
+    log("DANOS-TEST-BEGIN: clock\n", .{});
+
+    // Calibration produced a sane LAPIC frequency (roughly 1 MHz .. 100 GHz).
+    const lapic = arch.lapicHz();
+    check("LAPIC frequency measured", lapic > 1_000_000 and lapic < 100_000_000_000);
+
+    // Wait for ~5 real ticks and confirm uptime advanced by about that many ms
+    // (tick rate is 1000 Hz, so 1 tick == 1 ms).
+    const start_ticks = arch.ticks();
+    const start_ms = arch.uptimeMs();
+    var spins: u64 = 0;
+    while (arch.ticks() < start_ticks + 5 and spins < 5_000_000_000) spins +%= 1;
+    const elapsed_ms = arch.uptimeMs() - start_ms;
+    check("uptime advances with ticks", elapsed_ms >= 5 and elapsed_ms < 100);
+
+    result();
+}
+
 fn faultInvalidOpcode() void {
     log("DANOS-TEST-BEGIN: fault-ud\n", .{});
     asm volatile ("ud2");