Prevent USB commands from working when USB is stopped.
diff --git a/CHANGELOG b/CHANGELOG
index e981116..df1b6d0 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -2,6 +2,8 @@
 Changes since U-Boot 1.1.4:
 ======================================================================
 
+* Prevent USB commands from working when USB is stopped.
+
 * Add rudimentary handling of alternate settings of USB interfaces.
   This is in order to fix issues with some USB sticks or knives timing
   out during initialisation. Some code readability improvements.
diff --git a/common/cmd_usb.c b/common/cmd_usb.c
index fcc6662..28c05aa 100644
--- a/common/cmd_usb.c
+++ b/common/cmd_usb.c
@@ -444,6 +444,7 @@
 
 	int i;
 	struct usb_device *dev = NULL;
+	extern char usb_started;
 #ifdef CONFIG_USB_STORAGE
 	block_dev_desc_t *stor_dev;
 #endif
@@ -477,6 +478,10 @@
 		usb_stop();
 		return 0;
 	}
+	if (!usb_started) {
+		printf("USB is stopped. Please issue 'usb start' first.\n");
+		return 1;
+	}
 	if (strncmp(argv[1],"tree",4) == 0) {
 		printf("\nDevice Tree:\n");
 		usb_show_tree(usb_get_dev_index(0));
diff --git a/common/usb.c b/common/usb.c
index b1b7aec..0857494 100644
--- a/common/usb.c
+++ b/common/usb.c
@@ -72,6 +72,8 @@
 static int asynch_allowed;
 static struct devrequest setup_packet;
 
+char usb_started; /* flag for the started/stopped USB status */
+
 /**********************************************************************
  * some forward declerations...
  */
@@ -110,10 +112,12 @@
 		printf("scanning bus for devices... ");
 		running=1;
 		usb_scan_devices();
+		usb_started = 1;
 		return 0;
 	}
 	else {
 		printf("Error, couldn't init Lowlevel part\n");
+		usb_started = 0;
 		return -1;
 	}
 }
@@ -124,6 +128,7 @@
 int usb_stop(void)
 {
 	asynch_allowed=1;
+	usb_started = 0;
 	usb_hub_reset();
 	return usb_lowlevel_stop();
 }