Using gpio pins to drive transmitter

[Paul K. <ko...@cm...>]

Hello,

I am considering using the gpio pins on my Soekris net4501 single-board
computer to drive my homebrew transmitter, because the serial ports seem
to only work when used as a console.

The serial ports on my net4501 are driven by MAX3243C chips.  I cannot
measure any voltage on DTR when I set it high or low (using a python
module that works fine on my laptop).  It seems some revisions of the
net4501 have a way to inject power into the second serial port, but I
don't think I have that version.  I'm not sure what happens to DTR
during use as a console port, but obviously there's a way to get
standard RS232 signalling from these ports.  If anyone has an idea how
to do this, I'd truly appreciate a note or reference about it.

Some of the other serial port lines seem able to sink current, but these
are all receive-related and not controllable through the python
interface I used.  I haven't tried applying power to these pins while
toggling DTR.  If this strikes someone as likely to work, please let me
know.

The gpio pins can source up to 6mA, which is plenty to detect with an
emitter-follower circuit.  I have found user-space code to drive them.
How hard would it be to use lirc with these gpio pins?  Does lirc have a
userspace driver interface?  Would it be hard (for a veteran C
programmer but neophyte device driver hacker) to modify the lirc_serial
driver code?  I don't know much about serial port programming, and I'm a
 bit confused by all the serial port control flags used in lirc_serial.c
-- so I'm nervous about jumping in and changing things I don't understand.

Thank-you in advance for your time and help.

-Paul Komarek