correct handling of active devices

[hackapet/Adafruit_Blinka.git] / src / usb_hid.py

diff --git a/src/usb_hid.py b/src/usb_hid.py
index 4fff420400832f9219378ca4677f2be9c3be32ea..ae0e0aa2846afb2a79a9fa1b377318763fe6a78e 100644 (file)
--- a/src/usb_hid.py
+++ b/src/usb_hid.py
@@ -1,16 +1,51 @@
+"""
+`usb_hid` - support for usb hid devices via usb_gadget driver
+===========================================================
+See `CircuitPython:usb_hid` in CircuitPython for more details.
+For now using report ids in the descriptor
+
+# regarding usb_gadget see https://www.kernel.org/doc/Documentation/usb/gadget_configfs.txt
+* Author(s): Björn Bösel
+"""
+

 from typing import Sequence
 from pathlib import Path
 import os
 import atexit
 
 from typing import Sequence
 from pathlib import Path
 import os
 import atexit
 

-# https://www.kernel.org/doc/Documentation/usb/gadget_configfs.txt
+for module in ["dwc2", "libcomposite"]:
+    if Path("/proc/modules").read_text().find(module) == -1:
+        raise Exception(
+            "%s module not present in your kernel. did you insmod it?" % module
+        )
+
+gadget_root = "/sys/kernel/config/usb_gadget/adafruit-blinka"
+_boot_device = 0
+_active_devices = []
+

 
 

-gadget_root = '/sys/kernel/config/usb_gadget/adafruit-blinka'
+@property
+def devices():
+    return _active_devices

 
 
 
 

-class Device():
-    def __init__(self, *, descriptor: bytes, usage_page: int, usage: int, report_ids: Sequence[int],
-                 in_report_lengths: Sequence[int], out_report_lengths: Sequence[int]) -> None:
+def get_boot_device() -> int:
+    return _boot_device
+
+
+class Device:
+    """HID Device specification: see https://github.com/adafruit/circuitpython/blob/main/shared-bindings/usb_hid/Device.c"""
+
+    def __init__(
+        self,
+        *,
+        descriptor: bytes,
+        usage_page: int,
+        usage: int,
+        report_ids: Sequence[int],
+        in_report_lengths: Sequence[int],
+        out_report_lengths: Sequence[int],
+    ) -> None:

         self.out_report_lengths = out_report_lengths
         self.in_report_lengths = in_report_lengths
         self.report_ids = report_ids
         self.out_report_lengths = out_report_lengths
         self.in_report_lengths = in_report_lengths
         self.report_ids = report_ids


@@ -20,14 +55,21 @@ class Device():
         self._last_received_report = None
 
     def send_report(self, report: bytearray, report_id: int = None):
         self._last_received_report = None
 
     def send_report(self, report: bytearray, report_id: int = None):

+
+        report_id = report_id or self.report_ids[0]

         device_path = self.gets_device_path(report_id)
         device_path = self.gets_device_path(report_id)

-        with open(device_path, 'rb+') as fd:
-            fd.write(report)
+        with open(device_path, "rb+") as fd:
+            fd.write(bytearray(report_id) + report)

 
     @property
 
     @property

-    def last_received_report(self, ):
-        device_path = self.gets_device_path(self.report_ids[0])
-        with open(device_path, 'rb+') as fd:
+    def last_received_report(
+        self,
+    ) -> bytes:
+        return self.get_last_received_report()
+
+    def get_last_received_report(self, report_id=None) -> bytes:
+        device_path = self.gets_device_path(report_id or self.report_ids[0])
+        with open(device_path, "rb+") as fd:

             os.set_blocking(fd.fileno(), False)
             report = fd.read(self.out_report_lengths[0])
             if report is not None:
             os.set_blocking(fd.fileno(), False)
             report = fd.read(self.out_report_lengths[0])
             if report is not None:


@@ -35,93 +77,166 @@ class Device():
         return self._last_received_report
 
     def gets_device_path(self, report_id):
         return self._last_received_report
 
     def gets_device_path(self, report_id):

-        device = \
-            Path('%s/functions/hid.usb%s/dev' % (gadget_root, report_id or self.report_ids[0])) \
-                .read_text() \
-                .strip() \
-                .split(':')[1]
-        device_path = '/dev/hidg%s' % device
+        device = (
+            Path(
+                "%s/functions/hid.usb%s/dev"
+                % (gadget_root, report_id or self.report_ids[0])
+            )
+            .read_text()
+            .strip()
+            .split(":")[1]
+        )
+        device_path = "/dev/hidg%s" % device

         return device_path
 
 
 Device.KEYBOARD = Device(
         return device_path
 
 
 Device.KEYBOARD = Device(

-    descriptor=bytes((
-
-        0x05, 0x01,  # usage page (generic desktop ctrls)
-        0x09, 0x06,  # usage (keyboard)
-        0xa1, 0x01,  # collection (application)
-        0x05, 0x07,  # usage page (kbrd/keypad)
-        0x19, 0xe0,  # usage minimum (0xe0)
-        0x29, 0xe7,  # usage maximum (0xe7)
-        0x15, 0x00,  # logical minimum (0)
-        0x25, 0x01,  # logical maximum (1)
-        0x75, 0x01,  # report size (1)
-        0x95, 0x08,  # report count (8)
-        0x81, 0x02,  # input (data,var,abs,no wrap,linear,preferred state,no null position)
-        0x95, 0x01,  # report count (1)
-        0x75, 0x08,  # report size (8)
-        0x81, 0x01,  # input (const,array,abs,no wrap,linear,preferred state,no null position)
-        0x95, 0x03,  # report count (3)
-        0x75, 0x01,  # report size (1)
-        0x05, 0x08,  # usage page (leds)
-        0x19, 0x01,  # usage minimum (num lock)
-        0x29, 0x05,  # usage maximum (kana)
-        0x91, 0x02,  # output (data,var,abs,no wrap,linear,preferred state,no null position,non-volatile)
-        0x95, 0x01,  # report count (1)
-        0x75, 0x05,  # report size (5)
-        0x91, 0x01,  # output (const,array,abs,no wrap,linear,preferred state,no null position,non-volatile)
-        0x95, 0x06,  # report count (6)
-        0x75, 0x08,  # report size (8)
-        0x15, 0x00,  # logical minimum (0)
-        0x26, 0xff, 0x00,  # logical maximum (255)
-        0x05, 0x07,  # usage page (kbrd/keypad)
-        0x19, 0x00,  # usage minimum (0x00)
-        0x2a, 0xff, 0x00,  # usage maximum (0xff)
-        0x81, 0x00,  # input (data,array,abs,no wrap,linear,preferred state,no null position)
-        0xc0,  # end collection
-    )),
+    descriptor=bytes(
+        (
+            0x05,
+            0x01,  # usage page (generic desktop ctrls)
+            0x09,
+            0x06,  # usage (keyboard)
+            0xA1,
+            0x01,  # collection (application)
+            0x85,
+            0x01,  # Report ID (1)
+            0x05,
+            0x07,  # usage page (kbrd/keypad)
+            0x19,
+            0xE0,  # usage minimum (0xe0)
+            0x29,
+            0xE7,  # usage maximum (0xe7)
+            0x15,
+            0x00,  # logical minimum (0)
+            0x25,
+            0x01,  # logical maximum (1)
+            0x75,
+            0x01,  # report size (1)
+            0x95,
+            0x08,  # report count (8)
+            0x81,
+            0x02,  # input (data,var,abs,no wrap,linear,preferred state,no null position)
+            0x95,
+            0x01,  # report count (1)
+            0x75,
+            0x08,  # report size (8)
+            0x81,
+            0x01,  # input (const,array,abs,no wrap,linear,preferred state,no null position)
+            0x95,
+            0x03,  # report count (3)
+            0x75,
+            0x01,  # report size (1)
+            0x05,
+            0x08,  # usage page (leds)
+            0x19,
+            0x01,  # usage minimum (num lock)
+            0x29,
+            0x05,  # usage maximum (kana)
+            0x91,
+            0x02,  # output (data,var,abs,no wrap,linear,preferred state,no null position,non-volatile)
+            0x95,
+            0x01,  # report count (1)
+            0x75,
+            0x05,  # report size (5)
+            0x91,
+            0x01,  # output (const,array,abs,no wrap,linear,preferred state,no null position,non-volatile)
+            0x95,
+            0x06,  # report count (6)
+            0x75,
+            0x08,  # report size (8)
+            0x15,
+            0x00,  # logical minimum (0)
+            0x26,
+            0xFF,
+            0x00,  # logical maximum (255)
+            0x05,
+            0x07,  # usage page (kbrd/keypad)
+            0x19,
+            0x00,  # usage minimum (0x00)
+            0x2A,
+            0xFF,
+            0x00,  # usage maximum (0xff)
+            0x81,
+            0x00,  # input (data,array,abs,no wrap,linear,preferred state,no null position)
+            0xC0,  # end collection
+        )
+    ),

     usage_page=0x1,
     usage=0x6,
     report_ids=[0x1],
     in_report_lengths=[8],
     usage_page=0x1,
     usage=0x6,
     report_ids=[0x1],
     in_report_lengths=[8],

-    out_report_lengths=[1]
+    out_report_lengths=[1],

 )
 Device.MOUSE = Device(
 )
 Device.MOUSE = Device(

-    descriptor=bytes((
-
-        0x05, 0x01,  # Usage Page (Generic Desktop Ctrls)
-        0x09, 0x02,  # Usage (Mouse)
-        0xA1, 0x01,  # Collection (Application)
-        0x09, 0x01,  # Usage (Pointer)
-        0xA1, 0x00,  # Collection (Physical)
-        0x05, 0x09,  # Usage Page (Button)
-        0x19, 0x01,  # Usage Minimum (0x01)
-        0x29, 0x05,  # Usage Maximum (0x05)
-        0x15, 0x00,  # Logical Minimum (0)
-        0x25, 0x01,  # Logical Maximum (1)
-        0x95, 0x05,  # Report Count (5)
-        0x75, 0x01,  # Report Size (1)
-        0x81, 0x02,  # Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
-        0x95, 0x01,  # Report Count (1)
-        0x75, 0x03,  # Report Size (3)
-        0x81, 0x01,  # Input (Const,Array,Abs,No Wrap,Linear,Preferred State,No Null Position)
-        0x05, 0x01,  # Usage Page (Generic Desktop Ctrls)
-        0x09, 0x30,  # Usage (X)
-        0x09, 0x31,  # Usage (Y)
-        0x15, 0x81,  # Logical Minimum (-127)
-        0x25, 0x7F,  # Logical Maximum (127)
-        0x75, 0x08,  # Report Size (8)
-        0x95, 0x02,  # Report Count (2)
-        0x81, 0x06,  # Input (Data,Var,Rel,No Wrap,Linear,Preferred State,No Null Position)
-        0x09, 0x38,  # Usage (Wheel)
-        0x15, 0x81,  # Logical Minimum (-127)
-        0x25, 0x7F,  # Logical Maximum (127)
-        0x75, 0x08,  # Report Size (8)
-        0x95, 0x01,  # Report Count (1)
-        0x81, 0x06,  # Input (Data,Var,Rel,No Wrap,Linear,Preferred State,No Null Position)
-        0xC0,  # End Collection
-        0xC0,  # End Collection
-    )),
+    descriptor=bytes(
+        (
+            0x05,
+            0x01,  # Usage Page (Generic Desktop Ctrls)
+            0x09,
+            0x02,  # Usage (Mouse)
+            0xA1,
+            0x01,  # Collection (Application)
+            0x85,
+            0x02,  # Report ID (2)
+            0x09,
+            0x01,  # Usage (Pointer)
+            0xA1,
+            0x00,  # Collection (Physical)
+            0x05,
+            0x09,  # Usage Page (Button)
+            0x19,
+            0x01,  # Usage Minimum (0x01)
+            0x29,
+            0x05,  # Usage Maximum (0x05)
+            0x15,
+            0x00,  # Logical Minimum (0)
+            0x25,
+            0x01,  # Logical Maximum (1)
+            0x95,
+            0x05,  # Report Count (5)
+            0x75,
+            0x01,  # Report Size (1)
+            0x81,
+            0x02,  # Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
+            0x95,
+            0x01,  # Report Count (1)
+            0x75,
+            0x03,  # Report Size (3)
+            0x81,
+            0x01,  # Input (Const,Array,Abs,No Wrap,Linear,Preferred State,No Null Position)
+            0x05,
+            0x01,  # Usage Page (Generic Desktop Ctrls)
+            0x09,
+            0x30,  # Usage (X)
+            0x09,
+            0x31,  # Usage (Y)
+            0x15,
+            0x81,  # Logical Minimum (-127)
+            0x25,
+            0x7F,  # Logical Maximum (127)
+            0x75,
+            0x08,  # Report Size (8)
+            0x95,
+            0x02,  # Report Count (2)
+            0x81,
+            0x06,  # Input (Data,Var,Rel,No Wrap,Linear,Preferred State,No Null Position)
+            0x09,
+            0x38,  # Usage (Wheel)
+            0x15,
+            0x81,  # Logical Minimum (-127)
+            0x25,
+            0x7F,  # Logical Maximum (127)
+            0x75,
+            0x08,  # Report Size (8)
+            0x95,
+            0x01,  # Report Count (1)
+            0x81,
+            0x06,  # Input (Data,Var,Rel,No Wrap,Linear,Preferred State,No Null Position)
+            0xC0,  # End Collection
+            0xC0,  # End Collection
+        )
+    ),

     # Omitted for brevity.
     usage_page=0x1,
     usage=0x02,
     # Omitted for brevity.
     usage_page=0x1,
     usage=0x02,


@@ -131,19 +246,35 @@ Device.MOUSE = Device(
 )
 
 Device.CONSUMER_CONTROL = Device(
 )
 
 Device.CONSUMER_CONTROL = Device(

-    descriptor=bytes((
-        0x05, 0x0C,  # Usage Page (Consumer)
-        0x09, 0x01,  # Usage (Consumer Control)
-        0xA1, 0x01,  # Collection (Application)
-        0x75, 0x10,  # Report Size (16)
-        0x95, 0x01,  # Report Count (1)
-        0x15, 0x01,  # Logical Minimum (1)
-        0x26, 0x8C, 0x02,  # Logical Maximum (652)
-        0x19, 0x01,  # Usage Minimum (Consumer Control)
-        0x2A, 0x8C, 0x02,  # Usage Maximum (AC Send)
-        0x81, 0x00,  # Input (Data,Array,Abs,No Wrap,Linear,Preferred State,No Null Position)
-        0xC0,  # End Collection
-    )),
+    descriptor=bytes(
+        (
+            0x05,
+            0x0C,  # Usage Page (Consumer)
+            0x09,
+            0x01,  # Usage (Consumer Control)
+            0xA1,
+            0x01,  # Collection (Application)
+            0x85,
+            0x03,  # Report ID (3)
+            0x75,
+            0x10,  # Report Size (16)
+            0x95,
+            0x01,  # Report Count (1)
+            0x15,
+            0x01,  # Logical Minimum (1)
+            0x26,
+            0x8C,
+            0x02,  # Logical Maximum (652)
+            0x19,
+            0x01,  # Usage Minimum (Consumer Control)
+            0x2A,
+            0x8C,
+            0x02,  # Usage Maximum (AC Send)
+            0x81,
+            0x00,  # Input (Data,Array,Abs,No Wrap,Linear,Preferred State,No Null Position)
+            0xC0,  # End Collection
+        )
+    ),

     # Omitted for brevity.
     usage_page=0x0C,
     usage=0x01,
     # Omitted for brevity.
     usage_page=0x0C,
     usage=0x01,


@@ -151,28 +282,27 @@ Device.CONSUMER_CONTROL = Device(
     in_report_lengths=[2],
     out_report_lengths=[0],
 )
     in_report_lengths=[2],
     out_report_lengths=[0],
 )

-devices = [Device.KEYBOARD, Device.MOUSE, Device.CONSUMER_CONTROL]

 
 
 def disable() -> None:
     try:
 
 
 def disable() -> None:
     try:

-        Path('%s/UDC' % gadget_root).write_text('')
+        Path("%s/UDC" % gadget_root).write_text("")

     except FileNotFoundError:
         pass
     except FileNotFoundError:
         pass

-    for symlink in Path(gadget_root).glob('configs/**/hid.usb*'):
+    for symlink in Path(gadget_root).glob("configs/**/hid.usb*"):

         symlink.unlink()
 
         symlink.unlink()
 

-    for strings_file in Path(gadget_root).rglob('configs/*/strings/*/*'):
+    for strings_file in Path(gadget_root).rglob("configs/*/strings/*/*"):

         if strings_file.is_dir():
             strings_file.rmdir()
 
         if strings_file.is_dir():
             strings_file.rmdir()
 

-    for strings_file in Path(gadget_root).rglob('configs/*/strings/*'):
+    for strings_file in Path(gadget_root).rglob("configs/*/strings/*"):

         if strings_file.is_dir():
             strings_file.rmdir()
         if strings_file.is_dir():
             strings_file.rmdir()

-    for config_dir in Path(gadget_root).rglob('configs/*'):
+    for config_dir in Path(gadget_root).rglob("configs/*"):

         if config_dir.is_dir():
             config_dir.rmdir()
         if config_dir.is_dir():
             config_dir.rmdir()

-    for function_dir in Path(gadget_root).rglob('functions/*'):
+    for function_dir in Path(gadget_root).rglob("functions/*"):

         if function_dir.is_dir():
             function_dir.rmdir()
     try:
         if function_dir.is_dir():
             function_dir.rmdir()
     try:


@@ -181,13 +311,30 @@ def disable() -> None:
         pass
 
 
         pass
 
 

-# atexit.register(disable)
+atexit.register(disable)

 
 
 def enable(devices: Sequence[Device], boot_device: int = 0) -> None:
 
 
 def enable(devices: Sequence[Device], boot_device: int = 0) -> None:

+    """
+    Specify which USB HID devices that will be available. Can be called in boot.py, before USB is connected.
+    :param devices:
+    :param boot_device:
+    :return:
+    """
+    global _boot_device, _active_devices
+    _boot_device = boot_device
+
+    """ Enable usb_hid
+    shim for https://docs.circuitpython.org/en/latest/shared-bindings/usb_hid/index.html#usb_hid.enable
+
+    """

     if len(devices) == 0:
         disable()
         return
     if len(devices) == 0:
         disable()
         return

+
+    if boot_device > 0:
+        raise NotImplementedError("not supported yet")
+

     """
     1. Creating the gadgets
     -----------------------
     """
     1. Creating the gadgets
     -----------------------


@@ -223,16 +370,20 @@ def enable(devices: Sequence[Device], boot_device: int = 0) -> None:
         $ echo <manufacturer> > strings/0x409/manufacturer
         $ echo <product> > strings/0x409/product
     """
         $ echo <manufacturer> > strings/0x409/manufacturer
         $ echo <product> > strings/0x409/product
     """

-    Path('%s/functions' % gadget_root).mkdir(parents=True, exist_ok=True)
-    Path('%s/configs' % gadget_root).mkdir(parents=True, exist_ok=True)
-    Path('%s/bcdDevice' % gadget_root).write_text('%s' % 1)  # Version 1.0.0
-    Path('%s/bcdUSB' % gadget_root).write_text('%s' % 0x0200)  # USB 2.0
-    Path('%s/bDeviceClass' % gadget_root).write_text('%s' % 0x00)  # multipurpose i guess?
-    Path('%s/bDeviceProtocol' % gadget_root).write_text('%s' % 0x00)
-    Path('%s/bDeviceSubClass' % gadget_root).write_text('%s' % 0x00)
-    Path('%s/bMaxPacketSize0' % gadget_root).write_text('%s' % 0x08)
-    Path('%s/idProduct' % gadget_root).write_text('%s' % 0x0104)  # Multifunction Composite Gadget
-    Path('%s/idVendor' % gadget_root).write_text('%s' % 0x1d6b)  # Linux Foundation
+    Path("%s/functions" % gadget_root).mkdir(parents=True, exist_ok=True)
+    Path("%s/configs" % gadget_root).mkdir(parents=True, exist_ok=True)
+    Path("%s/bcdDevice" % gadget_root).write_text("%s" % 1)  # Version 1.0.0
+    Path("%s/bcdUSB" % gadget_root).write_text("%s" % 0x0200)  # USB 2.0
+    Path("%s/bDeviceClass" % gadget_root).write_text(
+        "%s" % 0x00
+    )  # multipurpose i guess?
+    Path("%s/bDeviceProtocol" % gadget_root).write_text("%s" % 0x00)
+    Path("%s/bDeviceSubClass" % gadget_root).write_text("%s" % 0x00)
+    Path("%s/bMaxPacketSize0" % gadget_root).write_text("%s" % 0x08)
+    Path("%s/idProduct" % gadget_root).write_text(
+        "%s" % 0x0104
+    )  # Multifunction Composite Gadget
+    Path("%s/idVendor" % gadget_root).write_text("%s" % 0x1D6B)  # Linux Foundation

     """
     2. Creating the configurations
     ------------------------------
     """
     2. Creating the configurations
     ------------------------------


@@ -267,12 +418,15 @@ def enable(devices: Sequence[Device], boot_device: int = 0) -> None:
 
     for i, device in enumerate(devices):
 
 
     for i, device in enumerate(devices):
 

-        config_root = '%s/configs/device.%s' % (gadget_root, 1)
-        Path('%s/' % config_root).mkdir(parents=True, exist_ok=True)
-        Path('%s/strings/0x409' % config_root).mkdir(parents=True, exist_ok=True)
-        Path('%s/strings/0x409/configuration' % config_root).write_text('my configuration')
-        Path('%s/MaxPower' % config_root).write_text('150')
-        Path('%s/bmAttributes' % config_root).write_text('%s' % 0x080)
+        config_root = "%s/configs/device.%s" % (gadget_root, 1)
+        Path("%s/" % config_root).mkdir(parents=True, exist_ok=True)
+        Path("%s/strings/0x409" % config_root).mkdir(parents=True, exist_ok=True)
+        Path("%s/strings/0x409/configuration" % config_root).write_text(
+            "my configuration"
+        )
+        Path("%s/MaxPower" % config_root).write_text("150")
+        Path("%s/bmAttributes" % config_root).write_text("%s" % 0x080)
+        _active_devices.append(device)

         """
         3. Creating the functions
         -------------------------
         """
         3. Creating the functions
         -------------------------


@@ -300,15 +454,17 @@ def enable(devices: Sequence[Device], boot_device: int = 0) -> None:
 
         # create functions
         for report_index, report_id in enumerate(device.report_ids):
 
         # create functions
         for report_index, report_id in enumerate(device.report_ids):

-            function_root = '%s/functions/hid.usb%s' % (gadget_root, report_id)
+            function_root = "%s/functions/hid.usb%s" % (gadget_root, report_id)

             try:
             try:

-                Path('%s/' % function_root).mkdir(parents=True)
+                Path("%s/" % function_root).mkdir(parents=True)

             except FileExistsError:
                 continue
             except FileExistsError:
                 continue

-            Path('%s/protocol' % function_root).write_text('%s' % report_id)
-            Path('%s/report_length' % function_root).write_text('%s' % device.in_report_lengths[report_index])
-            Path('%s/subclass' % function_root).write_text('%s' % 1)
-            Path('%s/report_desc' % function_root).write_bytes(device.descriptor)
+            Path("%s/protocol" % function_root).write_text("%s" % report_id)
+            Path("%s/report_length" % function_root).write_text(
+                "%s" % device.in_report_lengths[report_index]
+            )
+            Path("%s/subclass" % function_root).write_text("%s" % 1)
+            Path("%s/report_desc" % function_root).write_bytes(device.descriptor)

             """
             4. Associating the functions with their configurations
             ------------------------------------------------------
             """
             4. Associating the functions with their configurations
             ------------------------------------------------------


@@ -326,7 +482,7 @@ def enable(devices: Sequence[Device], boot_device: int = 0) -> None:
                 $ ln -s functions/ncm.usb0 configs/c.1
             """
 
                 $ ln -s functions/ncm.usb0 configs/c.1
             """
 

-            Path('%s/hid.usb%s' % (config_root, report_id)).symlink_to(function_root)
+            Path("%s/hid.usb%s" % (config_root, report_id)).symlink_to(function_root)

     """
     5. Enabling the gadget
     ----------------------
     """
     5. Enabling the gadget
     ----------------------


@@ -343,5 +499,5 @@ def enable(devices: Sequence[Device], boot_device: int = 0) -> None:
     $ echo s3c-hsotg > UDC
 
     """
     $ echo s3c-hsotg > UDC
 
     """

-    udc = next(Path('/sys/class/udc/').glob('*'))
-    Path('%s/UDC' % gadget_root).write_text('%s' % udc.name)
+    udc = next(Path("/sys/class/udc/").glob("*"))
+    Path("%s/UDC" % gadget_root).write_text("%s" % udc.name)