test.ml

open Core.Std
open Lwt

let usb_send_recv send recv =
  let device = USB.open_device_with ~vendor_id:0x0000
                                    ~product_id:0x0000 in
  let t =
    USB.claim_interface device 0

    >>=

      fun u -> (
        USB.bulk_send ~handle:device
                      ~endpoint:0x01 send 0 (String.length send)
      )

    >>=

      fun s -> (
        if s > 0 then
          USB.bulk_recv ~handle:device ~endpoint:0x81
                        recv 0 (String.length recv)
        else
          return (-1)
      )

    >>=

      fun l -> return (USB.release_interface device 0, l)

    >>=

      fun (rel, l) -> (
        let _ = (rel >>= (fun u -> return @@ USB.close device))
        in return l
      )

  in Lwt_main.run t
;;

let cmd = "\x00\x00\x00\x00\x00\x00\x00\x00"
and buf = String.make 500 (char_of_int 0) in
    let len = usb_send_recv cmd buf in
    len
    |> String.slice buf 0
    |> String.to_list
    |> List.map ~f:(fun c -> Printf.sprintf "%02X" @@ int_of_char c)
    |> String.concat ~sep:" "
    |> print_endline
    |> return
;;