Bit by bit parallel port control

["Tony Howat" <tony@i-r-genius.com>]

Hi Everyone,

I'm having problems controlling the parallel port on a bit-on bit-off basis 
for a relay switch on a control project.

Linux marmot 2.6.5-1.358 #1 Sat May 8 09:04:50 EDT 2004 i686 athlon i386 
GNU/Linux

I have tried using the /dev/port method and putb - I can seemingly set bits 
on the port OK. However, checking with a meter shows the line changing for a 
few milliseconds then returning to 0v. I need the levels to hold. I believe 
that's what SHOULD happen...

I figured the lp module may interfere, so removed that. No help. Currently 
lsmod shows:

w83781d                26240  0
i2c_sensor              2176  1 w83781d
i2c_amd756              4484  0
i2c_core               16388  3 w83781d,i2c_sensor,i2c_amd756
autofs4                10624  0
sunrpc                101064  1
forcedeth              10624  0
floppy                 47440  0
sg                     27552  0
scsi_mod               91344  1 sg
dm_mod                 33184  0
ati_remote              9228  0
ohci_hcd               14748  0
button                  4504  0
battery                 6924  0
asus_acpi               8472  0
ac                      3340  0
ext3                  102376  3
jbd                    40216  1 ext3

Board is an ASUS A72N266VM (nforce based). Build is fedora 2. I'm not 
running lpd or X etc. Any suggestions?

There's plenty of sample code around, so I'm pretty confident I'm doing 
things right. My test code is here :

http://www.i-r-genius.com/paralleltest.c

I suspect there's something odd going on. I aim to try the code on an older 
machine soon.

Any help or pointers appreciated,

--
Tony