From 24d1cf3bd658c6e940b631ec69b0a82a6b61f93f Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Tue, 5 Nov 2013 14:41:42 +1100
Subject: [PATCH] HAL_PX4: don't check USB for data if not connected

---
 libraries/AP_HAL_PX4/UARTDriver.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libraries/AP_HAL_PX4/UARTDriver.cpp b/libraries/AP_HAL_PX4/UARTDriver.cpp
index 9f1313828c..516016c0c8 100644
--- a/libraries/AP_HAL_PX4/UARTDriver.cpp
+++ b/libraries/AP_HAL_PX4/UARTDriver.cpp
@@ -418,6 +418,11 @@ void PX4UARTDriver::_timer_tick(void)
 
     if (!_initialised) return;
 
+    // don't try IO on a disconnected USB port
+    if (strcmp(_devpath, "/dev/ttyACM0") == 0 && !hal.gpio->usb_connected()) {
+        return;
+    }
+
     _in_timer = true;
 
     // write any pending bytes