Need to get control of an usb bar code scanner recognized as a usb keyboard

osvaldomarques · 10-12-2008, 09:17 PM

Hi Ladies and Gentlemen,

I have an usb bar code reader which emulates an standard usb keyboard. The kernel recognizes it on the boot-up and all the data from it is merged with the data from the keyboard.

I'm trying to write an application in user land using libusb to talk with this device but I can't obtain access because the device is already in use by the console.

Does anybody knows a way to prevent the kernel to configure this device, leaving it to an application?

My system is a Fedora 8 running kernel 2.6.26.5-28.fc8.

Thanks in advance.

Osvaldo.

pinniped · 10-14-2008, 05:55 AM

Use "lsusb" (you may need to install it) to get information on the device, them use that information to prevent the device from being claimed by a driver. Why is it being recognized as a keyboard - does it advertise USB HID capabilities?

osvaldomarques · 10-14-2008, 12:25 PM

Hi Pinniped,

Thank you for answer me! First of all, as I am using fedora 8, I already have lsusb tool installed and I could identify the usb device. The problem is this device is recognized as a HID during the kernel booting, ages before udev read its rules, where I guess I could prevent it to be installed as a keyboard.

Below there is a portion of 'dmesg' messages during boot showing the identification:

Code:

ACPI: PCI Interrupt 0000:00:1f.2[B] -> GSI 19 (level, low) -> IRQ 19
PCI: Setting latency timer of device 0000:00:1f.2 to 64
ACPI: PCI interrupt for device 0000:00:1f.2 disabled
usb 4-1: configuration #1 chosen from 1 choice
input: Hand Held Products 3800G as /class/input/input2
input,hidraw0: USB HID v1.10 Keyboard [Hand Held Products 3800G] on usb-0000:00:1d.2-1
hiddev96hidraw1: USB HID v1.10 Device [Hand Held Products 3800G] on usb-0000:00:1d.2-1
usb 4-1: New USB device found, idVendor=0536, idProduct=02e1
usb 4-1: New USB device strings: Mfr=1, Product=2, SerialNumber=8
usb 4-1: Product: 3800G
usb 4-1: Manufacturer: Hand Held Products
usb 4-1: SerialNumber: 08145D112D
ata_piix 0000:00:1f.2: version 2.12
ACPI: PCI Interrupt 0000:00:1f.2[B] -> GSI 19 (level, low) -> IRQ 19
ata_piix 0000:00:1f.2: MAP [ P0 P2 P1 P3 ]
PCI: Setting latency timer of device 0000:00:1f.2 to 64

Today I tried to boot with "nousb" kernel parameter and it didn't enable the device. However, I can't modprobe any usb modules after this boot.

I would like to prevent this device from being attached to normal HID input without kernel recompilation because, to maintain any non standard patch is a burden for the years to come.

pinniped · 10-15-2008, 02:12 AM

I don't know if there is an easier way (I haven't done it and I have no time to investigate), but here is a hint on how to do it by hacking the kernel:

http://wiki.nonpolynomial.com/Lightstone

Basically, you can add the VendorID:ProductID information to the internal HID Blacklist. Of course if there is a method for adding such information at run-time, that would be much better.

The article also mentions taking control via "libhid" (a userspace HID library).

osvaldomarques · 10-15-2008, 02:24 AM

Thank you, Pinniped,

I'll research your hint this morning and I will report the findings.

Again, thank you!

Osvaldo.

osvaldomarques · 11-22-2008, 11:15 PM

Hi people,

After a while, I came back to this project, and following your directions, I found this libhid-discuss thread where Brice Rebsamen has the same problem and after discover the solution, he posted an example for another bar code scanner.

Based on this example, I could detach the scanner to be used on my application.