diff --git a/src/main.c b/src/main.c
index cb38a58..2f2b619 100644
--- a/src/main.c
+++ b/src/main.c
@@ -84,12 +84,14 @@ static const char *usb_strings[] = {
 };
 
 static bool paused = true;
+
+volatile uint32_t millis = 0;
 void sys_tick_handler(void)
 {
+	++millis;
 	// TODO: measure frequency
 }
 
-
 static void usb_set_config(usbd_device *dev, uint16_t wValue)
 {
 	cdcacm_set_config(dev, wValue);