Getting a string descriptor for a USB device

Question

Under Windows 8.1, with LibUsb.getDeviceList(null,connectedDevices), I successfully get each and every USB device connected to my PC with the following code :

connectedDevices= new DeviceList();
if(LibUsb.getDeviceList(null,connectedDevices){
    selectedDevices= new LinkedList<Device>();
    deviceDescriptor= new DeviceDescriptor();
    pos=connectedDevices.iterator();
    while(pos.hasNext()){
        device=pos.next();
        if(LibUsb.getDeviceDescriptor(device,deviceDescriptor)==LibUsb.SUCCESS){
            selectedDevices.add(device);
            LibUsb.refDevice(device);
        }
    }
}
LibUsb.freeDeviceList(connectedDevices,false);

but when I want to retrieve a string descriptor for a specific device whose "iManufacturer" is not null with :

StringBuffer buffer=new StringBuffer(1000);
device=selectedDevices.getFirst();
LibUsb.getDeviceDescriptor(device, deviceDescriptor);
handle=new DeviceHandle();
if (LibUsb.open(device,handle)==LibUsb.SUCCESS) {   
    LibUsb.getStringDescriptorAscii(handle,deviceDescriptor.iManufacturer(),buffer);            
    manufacturerDescription=buffer.toString();                  
    LibUsb.close(handle);
}

I either get the LIBUSB.ERROR_NO_DEVICE error code in return to the openfunction, which I find strange for a device discovered only a few milliseconds before or the LIBSUSB.ERROR_INVALID_PARAM error code in return to getDescriptor. And using LibUsb.getStringDescriptor(handle,deviceDescriptor.iManufacturer(),(short)0x409,buffer)fails as well with the same error code...

With LibUsb.getStringDescriptor(handle,deviceDescriptor...), I succeed in getting the string for the manufacturer and the product for two out of seventeen devices which returns a non-null value for iManufacturerand iProduct. I thought the reason others weren't retrieved was linked to the 127 bytes limitation but using getStringDescriptorAscii(handle,deviceDesriptor...,buffer), with a buffer sized at 1000 bytes, isn't better.

What am I missing?

Answer 1

I think you got the methods wrong. Using getStringDescriptor instead should fix it. But I am not aware of a language id 1000. Nevertheless the casting to byte of a short should have been a dead giveaway. ;)