sys/bluetooth: add status update timer

This adds a timer to send status updates periodically in addition to
when the status changes. Since there is no guarantee that notifications
are received, we just keep sending them to be sure.

In the future, we could consider sending an ack back to the hub indicate
that the status change was received so that we don't have to do this.

Issue: pybricks/support#287

Author: dlech

lib/pbio/sys/bluetooth.c

@@ -189,6 +189,7 @@ static void reset_all(void) {
 }
 
 static PT_THREAD(pbsys_bluetooth_monitor_status(struct pt *pt)) {
+    static struct etimer timer;
     static uint32_t old_status_flags, new_status_flags;
     static send_msg_t msg;
 
@@ -198,9 +199,15 @@ static PT_THREAD(pbsys_bluetooth_monitor_status(struct pt *pt)) {
     // right after notifications are enabled.
     old_status_flags = ~0;
 
+    // Send status periodically as well in case a notification was missed due
+    // to bad RF environment or bug like https://crbug.com/1195592
+    etimer_set(&timer, clock_from_msec(500));
+
     for (;;) {
-        // wait for status to change
-        PT_WAIT_UNTIL(pt, (new_status_flags = pbsys_status_get_flags()) != old_status_flags);
+        // wait for status to change or timeout
+        PT_WAIT_UNTIL(pt, (new_status_flags = pbsys_status_get_flags()) != old_status_flags || etimer_expired(&timer));
+
+        etimer_restart(&timer);
 
         // send the message
         msg.context.size = pbio_pybricks_event_status_report(&msg.payload[0], new_status_flags);