Send HID report with PyUSB

Question

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UPDATE

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I managed to send the data properly. For anyone who ran into the same problem, I used the following code:

data=[0x00, 0x04, 0x04, 0xFF, 0xFF, 0xFF, 0x00, 0x00]
result=dev.ctrl_transfer(0x21, 0x9, wValue=0x200, wIndex=0x00, data_or_wLength=data)

(This is based on the answer posted here: link)

But I don't understand in detail, why I have to use

bmRequestType=0x21
bRequest=0x9
wValue=0x200

What is the explanation?

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Initial request:

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I'm desperately trying to send a simple report to a HID-device using PyUSB.

Using "SimpleHIDwrite" I confirmed that the device works just as expected. I want to send this data:

report ID: 00

data: [00, 04, 04, FF, FF, FF, 00, 00]

Sending data using SimpleHIDwrite

I'm quite new to Python and USB and I can't figure out how to do this using dev.ctrl_transfer or dev.write.

Also, there are some posts about sending data to HID devices, but I couldn't figure out how to solve my problem. How can I fix it?

Here are some more details:

 # Based on https://github.com/walac/pyusb/blob/master/docs/tutorial.rst

import usb.core
import usb.util

# Find our device
# dev = usb.core.find(idVendor=0xfffe, idProduct=0x0001)
dev = usb.core.find(idVendor=0x1781, idProduct=0x8c0)


# Was it found?
if dev is None:
    raise ValueError('Device not found')

dev.set_configuration()

cfg = dev[0]
intf = cfg[(0,0)]
ep = intf[0]

# dev.write(ep.bEndpointAddress, [0x00, 0x00,0x04,0x04,0xFF,0xFF,0xFF,0x00, 0x00], 1000)
# dev.ctrl_transfer(bmRequestType, bRequest, wValue=0, wIndex=0, data_or_wLength=None, timeout=None)

print("print ep")
print(ep)
print("print cfg")
print(cfg)
print("print intf")
print(intf)

And the result of the script above is this:

print ep
      ENDPOINT 0x81: Interrupt IN ==========================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x3 Interrupt
       wMaxPacketSize   :    0x8 (8 bytes)
       bInterval        :    0xa
print cfg
  CONFIGURATION 1: 100 mA ==================================
   bLength              :    0x9 (9 bytes)
   bDescriptorType      :    0x2 Configuration
   wTotalLength         :   0x22 (34 bytes)
   bNumInterfaces       :    0x1
   bConfigurationValue  :    0x1
   iConfiguration       :    0x0
   bmAttributes         :   0x80 Bus Powered
   bMaxPower            :   0x32 (100 mA)
    INTERFACE 0: Human Interface Device ====================
     bLength            :    0x9 (9 bytes)
     bDescriptorType    :    0x4 Interface
     bInterfaceNumber   :    0x0
     bAlternateSetting  :    0x0
     bNumEndpoints      :    0x1
     bInterfaceClass    :    0x3 Human Interface Device
     bInterfaceSubClass :    0x0
     bInterfaceProtocol :    0x0
     iInterface         :    0x0
      ENDPOINT 0x81: Interrupt IN ==========================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x3 Interrupt
       wMaxPacketSize   :    0x8 (8 bytes)
       bInterval        :    0xa
print intf
    INTERFACE 0: Human Interface Device ====================
     bLength            :    0x9 (9 bytes)
     bDescriptorType    :    0x4 Interface
     bInterfaceNumber   :    0x0
     bAlternateSetting  :    0x0
     bNumEndpoints      :    0x1
     bInterfaceClass    :    0x3 Human Interface Device
     bInterfaceSubClass :    0x0
     bInterfaceProtocol :    0x0
     iInterface         :    0x0
      ENDPOINT 0x81: Interrupt IN ==========================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x3 Interrupt
       wMaxPacketSize   :    0x8 (8 bytes)
       bInterval        :    0xa

Process finished with exit code 0

Answer 1

This is all you need to do HID with just PyUSB:

  def hid_set_report(dev, report):
      """ Implements HID SetReport via USB control transfer """
      dev.ctrl_transfer(
          0x21,  # REQUEST_TYPE_CLASS | RECIPIENT_INTERFACE | ENDPOINT_OUT
          9,     # SET_REPORT
          0x200, # "Vendor" Descriptor Type + 0 Descriptor Index
          0,     # USB interface № 0
          report # the HID payload as a byte array -- e.g. from struct.pack()
      )

  def hid_get_report(dev):
      """ Implements HID GetReport via USB control transfer """
      return dev.ctrl_transfer(
          0xA1,  # REQUEST_TYPE_CLASS | RECIPIENT_INTERFACE | ENDPOINT_IN
          1,     # GET_REPORT
          0x200, # "Vendor" Descriptor Type + 0 Descriptor Index
          0,     # USB interface № 0
          64     # max reply size
      )

There isn't any need to jump onto the library-wrappers-around-libraries bandwagon. Are you an engineer or what? Just read the documentation. The protocol is not going to change anytime soon.

Finally, yeah. All the four libusbhid's I've seen are written in disastrously horrible C and depend on yet even more libraries. For what is essentially 10 lines of code. Make your own decision.

Answer 2

Don't use PyUSB (unless you need other protocols too). Managing HID isn't difficult, but there is a much easier solution.

HIDAPI is a C-library which manages the protocol, and there is a Python wrapper available too.

Also, it hides the necessity to take control back from the operating system, which recognizes the HID protocol on connection, and install its own driver.