Getting Vendor ID and Product ID from Winusb

Question

I am trying to get the Vendor and Product IDs from a Winusb device and am getting accessviolationexception when trying to use the winusb_GetDesicriptor() and cannot figure out why I am getting that exception.

Here are my declarations:

    internal devInfo myDevInfo = new devInfo();
    USB_INTERFACE_DESCRIPTOR ifaceDescriptor;
    USB_DEVICE_DESCRIPTOR deviceDescriptor;


    internal struct USB_INTERFACE_DESCRIPTOR
    {
        internal Byte bLength;
        internal Byte bDescriptorType;
        internal Byte bInterfaceNumber;
        internal Byte bAlternateSetting;
        internal Byte bNumEndpoints;
        internal Byte bInterfaceClass;
        internal Byte bInterfaceSubClass;
        internal Byte bInterfaceProtocol;
        internal Byte iInterface;
    }


    [StructLayout(LayoutKind.Explicit, Size = 18, CharSet = CharSet.Auto)]
    internal struct USB_DEVICE_DESCRIPTOR
    {
        [FieldOffset(0)]internal byte bLength;
        [FieldOffset(1)]internal byte bDescriptorType;
        [FieldOffset(2)]internal ushort bcdUSB;
        [FieldOffset(4)]internal byte bDeviceClass;
        [FieldOffset(5)]internal byte bDeviceSubClass;
        [FieldOffset(6)]internal byte bDeviceProtocol;
        [FieldOffset(7)]internal byte bMaxPacketSize0;
        [FieldOffset(8)]internal ushort idVendor;
        [FieldOffset(10)]internal ushort idProduct;
        [FieldOffset(12)]internal ushort bcdDevice;
        [FieldOffset(14)]internal byte iManufacturer;
        [FieldOffset(15)]internal byte iProduct;
        [FieldOffset(16)]internal byte iSerialNumber;
        [FieldOffset(17)]internal byte bNumConfigurations;
    }

    [DllImport("winusb.dll", SetLastError = true)]
    internal static extern Boolean WinUsb_Initialize(SafeFileHandle DeviceHandle, ref IntPtr InterfaceHandle);

    [DllImport("winusb.dll", SetLastError = true)]
    internal static extern Boolean WinUsb_QueryInterfaceSettings(IntPtr InterfaceHandle, Byte AlternateInterfaceNumber, ref USB_INTERFACE_DESCRIPTOR UsbAltInterfaceDescriptor);

    [DllImport("winusb.dll", SetLastError = true)]
    internal static extern Boolean WinUsb_GetDescriptor(IntPtr InterfaceHandle, byte DescriptorType, byte Index, ushort LanguageID, ref USB_DEVICE_DESCRIPTOR UsbAltDeviceDescriptor, ulong BufferLength, ref long LengthTransferred);

And then here is the code I am trying to run:

deviceHandle = CreateFile
                   (devicePathName,
                   (GENERIC_WRITE | GENERIC_READ),
                   FILE_SHARE_READ | FILE_SHARE_WRITE,
                   IntPtr.Zero,
                   OPEN_EXISTING,
                   FILE_FLAG_OVERLAPPED,
                   0);

            success = WinUsb_Initialize(deviceHandle, ref myDevInfo.winUsbHandle);
            success = WinUsb_QueryInterfaceSettings(myDevInfo.winUsbHandle, 0, ref ifaceDescriptor);
            success = WinUsb_GetDescriptor(myDevInfo.winUsbHandle,
                           0x01,
                           (byte)deviceIndex,
                           0,
                           ref deviceDescriptor,
                           18,
                           ref lengthTransferred);

I am getting through the initialize and getting the values back from queryinterfacesettings, but getting the accessviolation on the GetDescriptor call

Answer 1

Read the documentation for WinUsb_GetDescriptor.

It looks like your parameters are not correct. To obtain the VID/PID, which is in the Device Descriptor, you will want to specify the USB_DEVICE_DESCRIPTOR_TYPE type for the second parameter (0x01). You also only need to specify the language ID if you are requesting a String Descriptor. The length for your device descriptor is wrong too, it should be 18 (ushort is 2 bytes, this is probably the reason for your access violation). You also want to use byte instead of Byte in your DeviceDescriptor struct, you don't want the .NET class representation of the byte, just the type value itself.

Here is updated code that may work for you:

success = WinUsb_GetDescriptor(myDevInfo.winUsbHandle,
                               0x01, 
                               (byte)deviceIndex,
                               0,
                               ref deviceDescriptor,
                               18,
                               ref lengthTransferred);