Re: [Libusb-devel] what does a LIBUSB_TRANSFER_STALL on control transfer mean?

[Tim R. <ti...@pr...>]

bob 295 wrote:
> I'm still very much a USB/libusb-1.0 newbie.
>
> I've been trying to teach myself the libusb-1.0 library against a Phidgets SBC 
> board.

OK, that tells us the computer you're running this on, but not the
device you are trying to communicate with.  What kind of device are you
trying to contact?

> This board comes with libusb-0.1 source code,  albeit a tad 
> difficult to follow.   The relevant libusb-0.1 call I'm trying to emulate in 
> async libusb-1.0 is:
>
> =========  begin Phidget lib snip =============
>  BytesWritten = usb_control_msg((usb_dev_handle *)phid->deviceHandle,
>                                         USB_ENDPOINT_OUT | USB_TYPE_CLASS |
> USB_RECIP_INTERFACE,
>                                         USB_REQ_SET_CONFIGURATION,
>                                         0x0200, /* value */
>                                         phid->deviceDef->pdd_iid, /* index*/
>                                         (char *)buffer,
>                                         phid->outputReportByteLength, /* size 
> */
>                                         500); /* FIXME? timeout */
> =========== end Phidget lib snip ===========
>
> Recently I tried programming an async control transfer message by adding some 
> modifications to the dpfp.c example (documented at 
> http://www.icanprogram.com/opndrs/phidgets/2012Apr13.html).

That sample is for a U.are.U 4000B fingerprint scanner.  Do you actually
have a U.are.U 4000B fingerprint scanner?  If not, then the sample code
is not going to be terribly helpful.


> The relevant code is:
>
> ========== begin my dpfp.c snip =============
>
> libusb_fill_control_setup(ctrlbuf, 
> 		LIBUSB_ENDPOINT_OUT | LIBUSB_REQUEST_TYPE_CLASS |
> 		LIBUSB_RECIPIENT_INTERFACE,
> 		0x09,
> 		0x0200,
> 		0,
> 		6);
>
> 	ctrlbuf[8]=0x1;

That sets up a control transfer, but it does not actually SEND the
command.  You need libusb_submit_transfer to send this command to the
device.

 
> What does it mean when the control transfer returns a LIBUSB_TRANSFER_STALL?

A stall means the device did not recognize your command.  Do you
actually have this device?

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.