-------- Hardware interface, overview ---------------------

The PCs parallel port has an interrupt request input, which is pin 10 on the
DSub-25 connector.
The old 'IBM PC Parallel Port FAQ' says this IRQ to be positive edge
triggered. The pin is said to be a TTL input.

'Interfacing the Standard Parallel Port' by Craig Peacock says "However like
always, some cards may trigger the interrupt on the high to low transition.".


-------- Joystick driver ----------------------------------

The current module allows you to use your transmitter as a joystick, too! So
you can use it via 'rctran2' OR via 'joystick' in crrcsim.


-------- Hardware interface, 1 ----------------------------

Here is one possibility, found on the pages describing the PPJoy-Driver for
Windows. It is said to work with every PPM signal with at least TTL level.

This one should work with PPJoy for windows and with rctran(1/2) for linux.

PPM signal -------680 Ohm--------+------------- Ack, Pin 10 DSub-25
                                 |
                               ----
                                /\
                               /  \ ZD 4,7
                               ----
                                 |
                                 |
GND       -----------------------+-------------- GND, Pin 18 DSub-25





-------- Hardware interface, 2 ----------------------------

I don't like a limiting diode, so I opted to use this:

                                        +------------ D0, Pin 2 DSub-25
                                        |
                                        |
                                       4k7
                                        |
                                        |
                                        +------------ Ack, Pin 10 DSub-25
                                        |
                                       /
                                     |/ C
                                   B |
PPM signal ---------10k---+-----+----+    General Purpose NPN
                          |     |    |                                      
                          |     |    |\ E
                         ---   47k     \
                     1nF ---    |       |
                          |     |       |
                          |     |       |
GND        ---------------+-----+-------+------------ GND, Pin 18 DSub-25


The software has to set D0 to output high level, which is done by the
driver in this directory. I do not know if PPJoy does currently support this
interface. Maybe an email to its author helps.


-------- Kernel 2.4.x -------------------------------------

Login as root.
Call 'make -f Makefile.24' in this directory to compile the module 'rctran2.o'.
Call 'make -f Makefile.24 install' to install it.
Call 'modprobe rctran2' to load the module,
'rmmod rctran2' to unload it.


-------- Kernel 2.6.x -------------------------------------

Copy Makefile.26 to Makefile, adjust 'KSRC' in its first line and call
   make
in this directory to compile the module 'rctran2.ko'.

After that (as root):

insmod ./rctran2.ko

I experienced building this module for 2.6.x to be more tricky than for
2.4.x. It worked after I compiled the whole kernel from source and used that.

-------- Troubleshooting ----------------------------------

On a second terminal, use 
  tail -f /var/log/syslog
to see debug messages.

Do
  rmmod parport_pc
if the parallel port irq is already in use.

I experienced that rctran2 did not work if parport_pc had been loaded before
on kernel 2.6.8. Maybe this is a bug in the kernel or the module? I had to
remove parport_pc.ko from /lib/modules/... to use rctran. 

