[Jack-Devel] jackd + /dev/inputevent sounds bad

Dear devels,
I am facing a strange issue with jackd.

I'm running a debian armhf board with the latest jackd2 from git. By 
default I loopback the capture and playback ports, the audio sounds good 
at low period size and everything runs smooth when I startup jackd and 
connect the ports using a custom script (called jackaudio). Now, the 
sound is crippled if an init script I recently made is running in 
background. The guilty init script is called read_usrbutton and reads a 
gpio line for button press (BeagleBoard xM rev.C).
What it does mainly

   BUTTONPATH="/dev/input/event0"
   cat $BUTTONPATH > /tmp/dump 2>1&
   THIS_VALUE=`tail -n1 /tmp/dump`

Then THIS_VALUE is checked for changes in a while loop every 50ms.

Why could this be? For crippled audio I mean that buffers are scrambled 
up. Neither read_usrbutton nor 'cat' use much CPU so it's not a problem 
of XRUNS.

FYI, jackaudio looks like

   killall jackd
   # setup McBSP2
   echo threshold | tee /sys/devices/68000000.ocp/49022000.mcbsp/dma_op_mode
   echo 320 | tee /sys/devices/68000000.ocp/49022000.mcbsp/max_rx_thres
   echo 320 | tee /sys/devices/68000000.ocp/49022000.mcbsp/max_tx_thres
   # enable max CPU freq
   echo -n performance | tee 
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
   # start jack
   sudo -u debian jackd -P62 -t2000 -dalsa -dhw:0 -r44100 -p64 -n2 -s 
-i4 -o4 > /var/log/jackaudio.log 2>&1 &
   sleep 8
   sudo -u debian jack_connect system:capture_1 system:playback_1 > 
/dev/null
   sudo -u debian jack_connect system:capture_3 system:playback_3 > 
/dev/null

Ideas?
Cheers
-- 

Dr. Leonardo Gabrielli, PhD student
A3Lab - Dept. Information Engineering
Università Politecnica delle Marche
via Brecce Bianche 12, 60131, Ancona, Italy
Skype: leonardo.gabrielli
Web: a3lab.dii.univpm.it/people/leonardo-gabrielli 
<http://a3lab.dii.univpm.it/people/leonardo-gabrielli>

1397234583.21501_0.ltw:2, <53481B88.6080503 at univpm dot it>