[LinuxPPS] How to get interrupt on parallel port working

[Bernhard Schiffner]

On Friday 19 September 2008 19:54:17 Paul Simons wrote:
...
> I am using the parallel port (pin 10 - ACK, pin 24 - ACK ground) and just
> going straight TTL.  Everything seems to register fine:
...
> However, no joy:
...

I tried to check this from the beginning.

I connect busy (Pin 11) to ground (Pin 24). I'll explain later why this.
I connect /ACK (Pin 10) to my puls source.
I apply (guaranteed single) negative pulses to the /ACK-Pin (Pin 10).
I test interrupts occuring like this:
bs2:~# cat /proc/interrupts | grep 7:

With a fresh booted Debian Lenny (minimal system):
bs2:~# cat /proc/interrupts | grep 7:
  7:          1    XT-PIC-XT        parport0
Apply pulses, but nothing increases.
	Module partport_pc	loaded
	Module partport	loaded
	No module lp
	No module ppdev
	No /dev/lp0

Next step:
	modprobe lp
	(creates /dev/lp0)
Apply pulses, nothing increases yet.

Next step:
	echo "A" > /dev/lp0
Apply pulses and HERE WE GO!
bs2:~# cat /proc/interrupts | grep 7:
  7:          2    XT-PIC-XT        parport0
bs2:~# cat /proc/interrupts | grep 7:
  7:          3    XT-PIC-XT        parport0

First trial of an explanation:
Module lp creates a "line discipline" which is in my case with interrupts 
enabled. Enabled doesn't mean useable from the very beginning!

The "lp" line discipline sets a certain type of handshake see
http://www.beyondlogic.org/spp/parallel.htm
This does
	1.) write data 
	2.) wait for busy (Pin 11) = low (already connected to ground, see above!)
	3.) make some flagging with strobe (Pin 1)
	4.) be ready  for the /ACK interrupt to continue with 1.)

If you don't connect the busy (Pin 11) to ground echo "A" /dev/lp0 blocks and 
is to be killed by ^C. Interrupts will be counted nevertheless.

If your lp.ko isn't compiled with interrupt enabled, try the ppdev.ko module. 
This creates /dev/parport0 and is easy to program from userspace. (ECP-mode 
of the parport possible, only single use of parport, interrupt ...) But  you 
have to program it. See for this:
$KERNELSOURCE/Documentation/parport-lowlevel.txt
$KERNELSOURCE/Documentation/parport.txt
http://www.beyondlogic.org/ecp/ecp.htm

The "lp magic" above seems minimal to me.

Hope this helps!

Bernhard