Steel Bank Common Lisp

Hello!

I'm trying to use a com port from sbcl.
My test code is as follows:

(defun tvs-open ()
  (let ((fd (sb-posix:open "/dev/ttyS3" sb-posix:o-noctty sb-posix:o-rdwr)))
       (setf *tvs-fd* fd))))  

(defun tvs-close ()
  (sb-posix:close *tvs-fd*))
      
(defun tvs-write ()  
  (cffi:with-foreign-object (buf :unsigned-char 512)
    (setf (cffi:mem-aref buf :unsigned-char 0) 2)
    (setf (cffi:mem-aref buf :unsigned-char 1) 1)
    (setf (cffi:mem-aref buf :unsigned-char 2) 3)
    (setf (cffi:mem-aref buf :unsigned-char 0) 2)
    (setf (cffi:mem-aref buf :unsigned-char 0) #xb0)
    (setf (cffi:mem-aref buf :unsigned-char 0) 3)
    (sb-unix:unix-write 1 buf 0 3)
    (sb-unix:unix-write 1 buf 3 3)))

(defun tvs-read ()  
  (cffi:with-foreign-object (buf :unsigned-char 512)
    (sb-unix:unix-read  *tvs-fd* buf 512)
    (dotimes (i 32) 
      (format t "~a " 
	      (cffi:mem-aref buf :unsigned-char i)))
    (terpri)))

Alternatively, I can 
(sb-sys:make-fd-stream fd :input :output :element-type '(unsigned-byte 8))
and then use READ-BYTE or WRITE-BYTE.

The problem is: reading works, writing doesn't.

UNIX-WRITE says NIL 9, that's "Bad file descriptor"
WRITE-BYTE complains that is't not a binary stream...

In the same time, C program

char buf[6];
int fd=open("/dev/ttyS3",O_NOCCTY,O_RDWR);
write(fd,buf,0,6);
perror("");

says "Success"...

What's wrong?

Thanks for any advice,
Dmitri