CAN'T ACCESS DEVICE

[Steve Losen]

In article <218 at mccc.UUCP> pjh at mccc.UUCP (Peter J. Holsberg) writes:
>
>I have a 3b2 direct-connected to a UNIX PC and to a second 3b2.  The
>UNIX PC's name is 'pc0'; the second 3b2's is 'mc3'.  pc0 is on tty14;
>mc3, on tty81.  Here are the relevant lines from BNU files:
>
...
>cu -ltty81 gets me a connected message, while cu -ltty14 gets "CAN'T
>ACCESS DEVICE".   ???
>
>I switched the wires between tty81 and 14.  Now cu -ltty[either] gets
>the "CAN'T ACCESS DEVICE".  ???
...
>-- 
>Peter Holsberg                  UUCP: {rutgers!}princeton!mccc!pjh
>Technology Division             CompuServe: 70240,334
>Mercer College                  GEnie: PJHOLSBERG
>Trenton, NJ 08690               Voice: 1-609-586-4800

The two most likely problems here are 1) lack of permissions or 2) lack  of
carrier detect (CD). (Or both, yuck!)

If  the "CAN'T ACCESS DEVICE" error prints immediately, you probably have a
permission problem. See who owns the /dev/tty files (it should be uucp) and
be sure that cu and uucico are setuid to uucp.

If  the error message appears after a delay of several seconds, the open is
timing out due to lack of carrier detect (CD). When the  3b2  opens  a  tty
port  it  raises  DTR and if CD is not up, the 3b2 waits for CD to come up.
Normally the 3b2 will wait FOREVER, but cu (and uucico) set an alarm before
attempting  to  open  the line. If the open doesn't return before the alarm
goes off, cu terminates with the "CAN'T ACCESS DEVICE" message.

Since you have a direct connection between your 3b2s you need to  construct
a  cable  that connects DTR at one end to CD at the other. You also need to
cross Send Data and Receive Data (The pin that one 3b2 sends data  on  must
obviously be connected to the pin that the other 3b2 reads data from.) This
is tricky with those crazy phone jack cables that AT&T uses.  You  can  get
the  desired cable by connecting two cables together. Use the adaptors that
convert the phone jack to the familiar 25  pin  RS232  connector.  Some  of
these  adaptors  are marked "acu modem" and some are marked "terminal". Try
this:

(3b2) (cable) (terminal adaptor)  (modem  adaptor)  (cable) (3b2)

Hopefully  you  can  find  a  modem and terminal adaptor that are different
sexes or put a sex-change adaptor in between them.

I've never seen a Unix PC.  Presumably it also has phone jacks so the above
advise might also work.

To ensure that signals are being raised on the "slave"  3b2  and  Unix  PC,
enable logins on the appropriate ports on those machines. You might want to
disable logins on the outgoing port  on  the  "master"  3b2  to  avoid  the
"babbling  getty  syndrome"  (Two machines simultaneously thinking that the
other machine is trying to login).
-- 
Steve Losen     scl at virginia.edu
University of Virginia Academic Computing Center