fix cpu consume at idle

lib/u_async.c

@@ -867,13 +867,10 @@ void uasync_poll(struct UASYNC* ua, int timeout_tb) {
         req_timeout.tv_usec = (timeout_tb % 10000) * 100;
     }
     
-    // Use minimum of requested and next timer if both finite
     struct timeval poll_timeout;
     if (timeout_tb < 0) {
-        // Infinite requested - use next timer if any
         poll_timeout = next_timeout;
     } else {
-        // Finite requested - min of requested and next
         if (next_timeout.tv_sec < req_timeout.tv_sec ||
             (next_timeout.tv_sec == req_timeout.tv_sec && next_timeout.tv_usec < req_timeout.tv_usec)) {
             poll_timeout = next_timeout;
@@ -881,6 +878,8 @@ void uasync_poll(struct UASYNC* ua, int timeout_tb) {
             poll_timeout = req_timeout;
         }
     }
+    if (poll_timeout.tv_sec == 0 && poll_timeout.tv_usec == 0 && timeout_tb > 0) poll_timeout = req_timeout;
+
     
     int timeout_ms;
     if (timeout_tb < 0 && (next_timeout.tv_sec > 0 || next_timeout.tv_usec > 0)) {