Re: [libusb] MCP2200 CDC claim interface

[Xiaofan C. <xia...@gm...>]

On Tue, Feb 11, 2014 at 8:26 PM, Xiaofan Chen <xia...@gm...> wrote:
> On Tue, Feb 11, 2014 at 2:24 PM, Balázs Grill <bal...@gm...> wrote:
>> Hello!
>>
>> I'm trying to access a microchip MCP2200 device using libusb (1.0.18). It is
>> a composite device with a HID, and a CDC interface. On linux (x86, x86_64,
>> armhf) it works without any problem. However, on windows (x86_64), claiming
>> the CDC interface (after a successful claim on the HID interface) with
>> libusb_claim_interface fails with -12 (LIBUSB_ERROR_NOT_SUPPORTED).
>> According to the API documentation this API should not return with this
>> error.
>>
>> What can cause this error?
>>
>> You can see the usb descriptor here:
>> https://gist.github.com/balazsgrill/3468976
>> Here, you can see the code I use to access the device:
>> https://github.com/balazsgrill/mcp2200/blob/master/src/mcp2200.c
>> The program fails in mcp2200_connect at line 384.
>
> Have you installed the supported driver for the
> CDC interface? You need to do that in order to
> use libusb under Windows.
>
> Ref: https://github.com/libusb/libusb/wiki/Windows#wiki-driver-installation
>
> The issue is that you can not use the CDC-ACM interface
> under Windows as a serial port once you use WinUSB driver
> to replace it.
>
> It seems to me a better approach is only to concentrate on
> the HID interface and leave the CDC-ACM interface to
> the OS to handle (be it Linux or Windows). Then you can
> write a Linux only or cross-platform utility to control the
> HID interface. In that case, you may not want to use libusb
> but rather HIDAPI which may be more suitable.

For others who are not that familiar with MCP2200:

Product page from Microchip
http://www.microchip.com/wwwproducts/devices.aspx?dDocName=en546923

Microchip's Linux CDC-ACM driver readme
http://ww1.microchip.com/downloads/en/DeviceDoc/mcp2200_linux_driver_readme.txt

Microchip has a Windows only utility to access the
HID interface for the following function.
Class 03h - HID: I/O control, EEPROM access, and
initial configuration

The HID interface command is documented here.
http://ww1.microchip.com/downloads/en/DeviceDoc/93066A.pdf

One simple example is here using HIDAPI.
https://github.com/Miceuz/USBtoUART/blob/master/mcp2200.c

I am not so sure if there are any Linux utility now to
access the HID interface to the full extent.

-- 
Xiaofan