Must be called!: usb_claim_interface must be called before you perform any operations related to this interface (like usb_set_altinterface, usb_bulk_write, etc).

Before any communication can occur with a device, it needs to be found. This is accomplished by finding all of the busses and then finding all of the devices on all of the busses:

struct usb_bus *busses;
usb_init();
usb_find_busses();
usb_find_devices();
busses = usb_get_busses();

After this, the application should manually loop through all of the busess and all of the devices and matching the device by whatever criteria is needed: