====== Frequently Asked Questions ======

----

===== could not initialize parallel port =====

If your parallel port display does not work, please run //lcd4linux -Fvv// and have a look at the output. if you get these messages:

<code>
HD44780: using ppdev /dev/lp0
HD44780: ioctl(/dev/lp0, PPCLAIM) failed: 22 Invalid argument
HD44780: could not initialize parallel port!
HD44780: start display failed!
</code>


then you did not read the documentation, because [[:HD44780|there]] it reads:

//Note that you have to use parport devices (usually /dev/parports/* or /dev/parport* with major number 99), the printer devices (/dev/printers/* or /dev/lp* with major number 6) do NOT work! //

So you have to change your lcd44linux.conf and replace the ''Port '/dev/lp0' // with //Port '/dev/parports/0' ''

If you don't have that you'll need to create it first with 'mknod /dev/parport0 c 99 0'.
===== Parallel port Permissions =====


// not approved yet // Of course, you have to had permission to use /dev/parport0
For some reason, changing the permission with chmod do not hold after a restart on some distribution.
Instead, you should just make sure the user that runs the program is in the lp
group.// not approved yet //

===== USB port permissions =====

If you get the message "usb_claim_interface() failed", you probably do not have sufficient user rights to access your display.  Here's how to solve it on Debian based systems that use "udev":

1. create the group "lcdusers" by running

<code>
# sudo groupadd --system lcdusers
</code>


2. add yourself to this group

<code>
# sudo usermod --append --groups lcdusers your_username
</code>


3. find the "idVendor" values for your display (in this case "04d8" and "c002" for the "picoLCD 256x64"):

<code>
# lsusb
Bus 003 Device 002: ID 04d8:c002 Microchip Technology, Inc.
</code>


4. create the file "/etc/udev/rules.d/60-lcd.rules" with the following contents (you'll of course have to change the "idVendor" and "idProduct"):

<code>
SUBSYSTEM!="usb_device", ACTION!="add", GOTO="lcd_rules_end"
# picoLCD
SYSFS{idVendor}=="04d8", SYSFS{idProduct}=="c002", GROUP="lcdusers", MODE="0660"
LABEL="lcd_rules_end"
</code>


5. it might be necessary to reboot your system.  Then run "ls -l /dev/usb/" to verify that your display is in the "lcd_users" group:

<code>
# ls -l /dev/usb/
total 0
crw-rw---- 1 root lcdusers 180, 96 2010-01-20 13:55 hiddev0
</code>


6. enjoy your new display... :)

----

===== cygwin: compile lcd4linux =====

Not all plugins works well with cygwin:

<code>
./configure --with-drivers=VNC,NULL --with-plugins='all,!dvb,!i2c_sensors,pop3'
</code>


Now it works like a charm...