[usb_gadget p01] Functions for encoding HID descriptors.

tools/usb_gadget/usb_descriptors.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """USB descriptor generation utilities.
 
 Classes to represent and generate USB descriptors.
 """
 
 import struct
 
+import hid_constants
 import usb_constants
 
 
 class Field(object):
   """USB descriptor field information."""
 
   def __init__(self, name, str_fmt, struct_fmt, required):
     """Define a new USB descriptor field.
 
     Args:
@@ skipping 345 matching lines @@
                 for typ, length in self._descriptors)
     return ''.join(bufs)
 
   def __str__(self):
     return '{}\n{}'.format(
         super(HidDescriptor, self).__str__(),
         '\n'.join('  bDescriptorType: 0x{:02X}\n  wDescriptorLength: {}'
                   .format(typ, length) for typ, length in self._descriptors))
 
 HidDescriptor.AddComputedField('bLength', 'B', 'struct_size')
-HidDescriptor.AddFixedField('bDescriptorType', 'B', 33)
+HidDescriptor.AddFixedField('bDescriptorType', 'B',
+                            hid_constants.DescriptorType.HID)
 HidDescriptor.AddField('bcdHID', 'H', default=0x0111, str_fmt='0x{:04X}')
 HidDescriptor.AddField('bCountryCode', 'B', default=0)
 HidDescriptor.AddComputedField('bNumDescriptors', 'B', 'num_descriptors')