(define (hackrf-start-rx ctx d stream-processor)
  (let ([ctlin (second ctx)]
        [ctlout (third ctx)]
        [r (fourth ctx)])
    (displayln
     (string-append "startrx " d) ctlin)
    (flush-output ctlin)
    (sleep 0.1)
    (let ([line (read-line ctlout)])
      (if (not (equal? line "creating stream"))
          (raise line)
          (let ([dataout (open-input-file
                          (string-append "/tmp/hackrfkern-"
                                         r
                                         "/dataout-"
                                         d))])
            (thread
             (lambda ()
               (letrec ([loop (lambda ()
                                (if (eof-object? (peek-byte dataout))
                                    (void)
                                    (let* ([line (read-line dataout)]
                                           [tokens (string-split line)])
                                      (if (or (not (= (length tokens) 3))
                                              (not (string=? (car tokens) "rx")))
                                          (raise (string-append "bad prefix in RX stream: " line))
                                          (stream-processor dataout (string->number (third tokens))))
                                      (loop))))])
                 (loop)))))))))

(define (sp-to-file path)
  (let* ([out (open-output-file path)]
         [buffer-size 100000]
         [buffer (make-bytes buffer-size)])
    (lambda (in nbytes)
      (if (> nbytes buffer-size)
          (begin
            (set! buffer-size nbytes)
            (set! buffer (make-bytes buffer-size)))
          (void))
      (read-bytes! buffer in 0 nbytes)
      (write-bytes buffer out 0 nbytes))))