network based console?

Till Straumann strauman at
Fri Sep 12 16:52:08 UTC 2008

If you want to redirect your system console to a TCP/IP socket
then you have to consider a few gotchas:

 - 'printk' will never be possible; printk normally uses a polling
   driver for the serial port enabling it to be called everywhere
   (w/o task context, from an ISR, before system is up etc.).
   Unless you have a second networking
   IF and implement a special polling driver + protocol stack there
   you're not going to have printk.

 - you should be able to replace fds 0,1,2 with a TCP socket so
   that all stdio goes over that connection.

 - HOWEVER: the RTEMS file-system per se is not thread-safe
   and RTEMS sockets are not. Therefore, you'd need to somehow
   add locking; so you'd probably have to write a small 'driver'
   wrapping a mutex lock/unlock pair around read/write from/to
   the socket.

 - NOTE: RTEMS/newlib's FILE buffers are global, unprotected
   objects and sharing them among threads is not safe (unless
   you add locking yourself).
   BUT: the stdin/stdout/stderr streams/buffers are
   exceptional: every thread has it's own set of 3 buffers (all
   sharing the underlying file descriptors 0,1,2).

-- Till

Gene Smith wrote:
> Right now my stdin and stdout operations go in/out the serial port. 
> However, my serial port *must* go away since it is multiplexed with a 
> more essential function that replaces it. However, my ethernet tcp/ip is 
> working well now. Is it possible to setup a remote terminal using tcp/ip 
> that will act as stdin/stdout for my board running rtems? This would 
> mainly be for debug or control purposes and probably not kept in the 
> final version.
> In the past, I have used syslog to record debug messages on a remote 
> system (output only) via UDP. I see mention of a telnetd for rtems that 
> might allow me to connect to the rtems board but not sure that the 
> remote telnet terminal functions the same as the remote serial terminal 
> (ie, gtkterm, minicom, etc), i.e., printf's output to it and keystroke 
> are input back to rtems.
> I expect this is all bound in with termios and the console driver and 
> network driver but not sure how it all ties together or if what I want 
> is possible. I will keep looking. But any advance information or 
> comments would be appreciated.
> -gene
> _______________________________________________
> rtems-users mailing list
> rtems-users at

More information about the users mailing list