added tud_task_event_ready()

to check if there is pending events in the tud task without executing
it. Useful to check before entering low power mode with WFI/WFE

src/device/usbd.c

@@ -339,6 +339,14 @@ static void usbd_reset(uint8_t rhport)
   }
 }
 
+bool tud_task_event_ready(void)
+{
+  // Skip if stack is not initialized
+  if ( !tusb_inited() ) return false;
+
+  return !osal_queue_empty(_usbd_q);
+}
+
 /* USB Device Driver task
  * This top level thread manages all device controller event and delegates events to class-specific drivers.
  * This should be called periodically within the mainloop or rtos thread.

src/device/usbd.h

@@ -47,6 +47,9 @@ bool tud_init (void);
 // Task function should be called in main/rtos loop
 void tud_task (void);
 
+// Check if there is pending events need proccessing by tud_task()
+bool tud_task_event_ready(void);
+
 // Interrupt handler, name alias to DCD
 #define tud_int_handler   dcd_int_handler