feat: pit timer

1 files changed, 17 insertions, 0 deletions

diff --git a/boot/timer.zig b/boot/timer.zig
new file mode 100644
index 0000000..4569d6a
--- /dev/null
+++ b/boot/timer.zig
@@ -0,0 +1,17 @@
+// PIT channel 0 tick counter
+// configuring the PIT itself (outb to 0x43/0x40) is done in revo (kernel
+// `pit_init`), since it's just port writes the VM can drive
+
+var ticks: u64 = 0;
+
+// called from the IRQ0 handler
+pub fn onIrq() void {
+    const t: *volatile u64 = &ticks;
+    t.* +%= 1;
+}
+
+// called from the event loop
+pub fn now() u64 {
+    const t: *volatile u64 = &ticks;
+    return t.*;
+}