diff -r 8992134dcfd0 tools/python/xen/xm/main.py
--- a/tools/python/xen/xm/main.py	Wed Aug 04 19:24:17 2010 +0100
+++ b/tools/python/xen/xm/main.py	Fri Aug 06 18:02:33 2010 +0800
@@ -225,8 +225,8 @@
     'usb-list'    :  ('<Domain>',
                         'List domain\'s attachment state of all virtual port .'),
     'usb-list-assignable-devices' : ('', 'List all the assignable usb devices'),
-    'usb-hc-create'  :  ('<Domain> <USBSpecVer> <NumberOfPorts>',
-                        'Create a domain\'s new virtual USB host controller.'),
+    'usb-hc-create'  :  ('<Domain> <USBSpecVer> <NumberOfPorts>\n       ## <USBSpecVer>: 2 (for USB2.0), 1 (for USB1.1)',
+                         'Create a domain\'s new virtual USB host controller.'),
     'usb-hc-destroy'  :  ('<Domain> <DevId>',
                         'Destroy a domain\'s virtual USB host controller.'),
 
@@ -3064,6 +3064,8 @@
     ver = args[1]
     num = args[2]
     vusb_config = ['vusb']
+    if not re.match('^\d{1}$', ver):
+	print "Invalid usb-ver format '%s'" % ver
     vusb_config.append(['usb-ver', str(ver)])
     vusb_config.append(['num-ports', str(num)])
     port_config = ['port']