Index: sys/boot/kshim/bsd_kernel.c
===================================================================
--- sys/boot/kshim/bsd_kernel.c
+++ sys/boot/kshim/bsd_kernel.c
@@ -138,6 +138,7 @@
 {
 	int start = ticks;
 	int delta;
+	int time = 0;
 
 	if (cv->sleeping)
 		return (EWOULDBLOCK);	/* not allowed */
@@ -155,6 +156,14 @@
 		usb_idle();
 
 		mtx_lock(mtx);
+
+		if (++time >= (1000 / hz)) {
+			time = 0;
+			callout_process(1);
+		}
+
+		/* Sleep for 1 ms */
+		delay(1000);
 	}
 
 	if (cv->sleeping) {