Re: 2.6.25.3: serial problem (minicom)

R.L. Horn
2008-06-20T11:23:28Z

On Fri, 20 Jun 2008, Hans-Peter Jansen wrote:

> Alan, I got to test this by applying the changeset (Olivier, many thanks
> for your valuable hint, I'm sure, I will reuse this knowledge soon), to
> the otherwise unchanged kernel, but unfortunately, it doesn't solve my
> issue.
>
> A different patch must have changed the behavior/state of some RS232 lines
> in the 2.6.25 time frame,

There was a deliberate change in DTR behavior, though I'm not up on the
details. If you have a copy of 2.6.25.something handy and want to check
that that's the problem, you might look at drivers/serial/serial_core.c.
Round about line 2160 (in uart_configure_port()), you'll see:

/*
* Ensure that the modem control lines are de-activated.
* keep the DTR setting that is set in uart_set_options()
* We probably don't need a spinlock around this, but
*/
spin_lock_irqsave(&port->lock, flags);
port->ops->set_mctrl(port, port->mctrl & TIOCM_DTR);

Change the last line to:

port->ops->set_mctrl(port, 0);

which reverts to 2.6.24 behavior.

If your problem isn't resolved here, please contact me off-list with some
details about your receiver, ntpd version, etc. and I'll look into it
further. I've been thinking about building a WWVB doodad, and a solution
to this might save me some grief later on.

> As another data point: using a usb <-> rs232 converter, the dcf device
> got back to life again. It still doesn't work in its entirety, but at
> least, some data arrives in ntpd. Expected is something similar to:
> -#--#-#####-###--D--S124--2-p------p-----21-4-24-----8-- (incomplete)
> but it reads:
> ###############RADMLS1248124P124812P1248121241248112481248P
> thus, obviously it doesn't get any 0 values back (displayed as - above).

That looks like a hardware problem. Odds are, something here (and it
could be the USB<->RS232 converter or the DCF receiver or both) either
isn't up to RS-232 specs or the receiver is making unfounded assumptions
about the DTE port. In particular, I'd want to know the mark/space
voltages coming out of that USB thingy.