Re: usb_control_msg returns -32

On Wednesday 06 July 2005 3:38 pm, Sandro Weiser wrote:
> we are developing a driver for shuttle lcd's for lcdproc:
> http://www-user.tu-chemnitz.de/~sawei/twiki/bin/view/Projekte/ShuttleLCD
> 
> What we do:
> 
> usb_init();
>   usb_find_busses();
>   usb_find_devices();
>   busses = usb_get_busses();
> 
>   /* on all busses look for Shuttle VFD's */
>   p->udh = NULL;
>   for (bus = busses; bus != NULL; bus = bus->next) {
>     struct usb_device *dev;
> 
>     for (dev = bus->devices; dev; dev = dev->next) {
>       /* Check if this device is a Shuttle VFD */
>       if ( (dev->descriptor.idVendor == shvfdVendor) &&
>          (dev->descriptor.idProduct == shvfdProd) ) {
> 
>         /* Shuttle VFD found; try to find it's description and serial number 
> */
>         p->udh = usb_open(dev);
>         if (p->udh == NULL) {
>           report(RPT_WARNING, "PT6314: unable to open device");
> 
> ...
> 
>   if (p->udh != NULL) {
>     debug(RPT_DEBUG, "PT6314: opening device succeeded\n");
> 
>     if (usb_set_configuration(p->udh, 1) < 0) { /* set bConfigurationValue=1 
> */
>       usb_close(p->udh);
>       report(RPT_ERR, "PT6314: unable to set configuration");
>       return -1;
>     }
> 
>     if (usb_claim_interface(p->udh, 1) < 0) { /* claim bInterfaceNumber=1 */
> #if defined(LIBUSB_HAS_DETACH_KERNEL_DRIVER_NP)
>       if ((usb_detach_kernel_driver_np(p->udh, 1) < 0) ||
>           (usb_claim_interface(p->udh, 1) < 0)) {
>         usb_close(p->udh);
>         report(RPT_ERR, "PT6314: unable to re-claim interface");
>         return -1;
>       }
> #else
>       usb_close(p->udh);
>       report(RPT_ERR, "PT6314: unable to claim interface");
>       return -1;
> #endif
>     }
>   }
>   else {
>     report(RPT_ERR, "PT6314: no (matching) ShuttleVFD device found");
>     return -1;
>   }
> 
> ...
> 
>   /* USB_DT_HID         0x21 */
>   /* USB_REQ_SET_REPORT 0x09 */
>   int ret;
>   ret = usb_control_msg(udh, USB_DT_HID, USB_REQ_SET_REPORT, 0, 1,
>                         data, 8, shvfdTimeout);
>   if (8 == ret)
>     return PT6314_OK;
>   else {
>     debug(RPT_DEBUG, "only %d bytes written", ret);
>     return PT6314_ERROR;
>   }
> }
> 
> but usb_control_msg returns only -32 (only -32 bytes written)
> 
> What does this mean?
> 
> int usb_control_msg(usb_dev_handle *dev, int requesttype, int request, int 
> value, int index, char *bytes, int size, int timeout);
> 
> we are also not sure about value = 0 and index = 2
> where can we find doku for these 2 parameters, especially  the value parameter
> 
> thx

   Hello again.  Generally, functions returning <0 indicate an error condition.
The standard error numbers and their meanings can be found in:

(an example hierarchy from my system)
/usr/include/errno.h
	/usr/include/bits/errno.h
		/usr/include/linux/errno.h
			/usr/include/asm/errno.h
				/usr/include/asm-generic/errno.h
					/usr/include/asm-generic/errno-base.h

   This will be dependent upon how the distribution has headers set up.  You can view
this file online via kernel source trees located at http://www.kernel.org/git:

http://kernel.org/git/?p=linux/kernel/git/gregkh/linux-2.6.11.y.git;a=blob;h=65115978510ff2a2a8f6cd3610007b844746be78;hb=8e63197ffe7750c94c8ea9d159ce3e46a76bfcf2;f=include/asm-generic/errno-base.h

    As for your inquery into wIndex and wValue, a good place to start is in the usb 1.1 specification.
Specifically, chapter 9 -section 3.  The usb 1.1 spec is available to developers here:

http://www.usb.org/developers/docs/
  (near the bottom)

	Best of luck,
		Lonnie Mendez

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