DMX_lag_fix

Since there is a massive DMX lag, here some approaches to fix it:
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There is a discussion on this thread:
https://github.com/OpenLightingProject/ola/issues/1677

Latency testing see here:
https://github.com/lemariva/rPI-Tests


1.Use a realtime kernel and do some tests:
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cd /
wget http://fps.io/raspberrypi4-linux-4.19.65-rt24-v7l+-usb-lowlatency.tar.gz
sudo tar xzf raspberrypi4-linux-4.19.65-rt24-v7l+-usb-lowlatency.tar.gz
sudo reboot

#make performance tests
#test if usb, ftp, hdmi audio, openframeworks is still working


2.Compile newest version of OLA including the patch from @shenghaoyang, create a *.deb file for easy update
   currently installed is version 0.10.3 without any patches
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#make sure you run as a user and not as root!

#completely remove ola and olad version 10.3, proceed with caution since this must be done destructive:

sudo apt-get purge ola -y
sudo rm -rf /usr/local/bin/ola*
sudo rm -rf /etc/ola
sudo rm -rf /usr/share/ola*
sudo rm -rf /usr/local/share/ola*
sudo rm -rf /usr/local/bin/ola*
sudo rm -rf /usr/local/include/ola*
sudo rm -rf /etc/init.d/olad
sudo rm -rf /usr/local/lib/libola*
sudo rm -rf /usr/local/lib/pkgconfig/libola*
sudo rm -rf /var/lib/ola*
sudo apt-get clean -y
sudo apt-get autoclean -y
#sudo apt-get autoremove -y




#then grab the newest version from git
#git clone https://github.com/OpenLightingProject/ola.git
#get the patched version from henghaoyang,

git clone https://github.com/shenghaoyang/ola.git
cd ola
git checkout mitigate-drift 
autoreconf -i
make clean
./configure
make -j 4 all
sudo make install
sudo ldconfig

#create the olad service file:
#not needed when later installed via .deb package
sudo nano /etc/systemd/system/olad.service
#content of the file: https://gist.github.com/magdesign/8525b4cda58d5862b80e1098bd1f2547


#create a *.deb file (worls only when wifi is turned off and network to dhcp and unplugged!):

autoreconf -i
./configure
make dist
cp ola-0.X.Y.tar.gz /tmp
cd /tmp
tar -zxf ola-0.X.Y.tar.gz
mv /tmp/ola-0.10.7.tar.gz /tmp/ola_0.10.7.orig.tar.gz
cd ola-0.X.Y
debuild



3.Stop all tasks which are not essential for dmx playback
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#kill samba
sudo kill $(pgrep 'smbd')

#kill shellinabox
service shellinabox stop

#shut down webserver: lighttpd, hostapd
#

#shut down php-cgi, php
#


4.Reserve 2 threads on boot and the use them only for dmx playback
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sudo nano /boot/cmdline.txt 
#and add this:
isolcpus=3,4
#which frees core 3 + 4
#then run ola on this free core
taskset -c 3 ./ola_record

5. run the audio player on thread 4
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#instead of omxplayer use a more lightweight one: aplay or mpg123 (check with htop)


5.Use usb stick to store dmx data
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check if this will be more performant

6.create ramdisk and copy dmx file to ram
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check if this will be more performant (size will be limited!!)


7. Add turbo mode to boot overlay
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# turbo mode will never throttle the cpu down and generates more heat!

sudo nano /boot/config.txt
#add
force_turbo=1
#if it will not boot anymore, hold down shift key while booting!


8. increase swap to 1024
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sudo nano /etc/dphys-swapfile

# replace  CONF_SWAPSIZE=100
# with CONF_SWAPSIZE=1024

# reload swap with:
sudo /etc/init.d/dphys-swapfile stop
sudo /etc/init.d/dphys-swapfile start
# this takes some minute