[Libusb-devel] reading from a barcode scanner that acts like a keyboard

[Brice R. <bri...@gm...>]

Hello,

I have a USB barcode scanner that acts like a keyboard: whenever a
barcode is read it sends the code where the keyboard would normally
write. I am writing some code in C to read from the scanner. This is
my first application using libusb, and it is the first time I am
working with a USB device.
I found out how to open the usb device, detach the kernel driver and
claim the interface. I got this information by reading the code of the
phidget library that makes use of libusb. To read from the phidgets
they call usb_interrupt_read. So I am doing the same but I get
nothing, although I am managing to read 8 bytes, always the same: 0 0
30 0 0 0 0 0
What's wrong? I pasted my code below (I removed error checking code).

One more question (not so important):
When detaching the kernel driver, it returns an error if it had been
previously detached. How to check that and make the distinction with
other kind of errors?
Or:
How to reattach the driver at the end?

Thanks,
Brice



int main(){
 usb_dev_handle *udev;
 struct usb_bus *bus;
 struct usb_device *dev;
 char barcode[8];

 // search for the scanner, open the device and claim interface
 usb_init();
 usb_find_busses();
 usb_find_devices();
 for( bus=usb_get_busses(); bus; bus = bus->next )
   for( dev = bus->devices; dev; dev = dev->next )
     if( dev->descriptor.idVendor==0x5e0 && dev->descriptor.idProduct==0x200 )
       udev = usb_open(dev);
 usb_detach_kernel_driver_np(udev, 0);
 usb_claim_interface(udev, 0);

 //prompt scanner until we get 8 bytes.
 while( usb_interrupt_read(udev,1,barcode,8,1000)!=8 );

 int i;
 printf("barcode: ");
 for( i=0; i<8; i++ ) printf("%u ",barcode[i]);
 printf("\n");

 usb_release_interface(udev, 0);
 usb_close(udev);
 return 1;
}