Dear,

I have tried to run python script but I have encountered a problem:

root@OpenWrt:~# python lcd3.py
Traceback (most recent call last):
  File "lcd3.py", line 70, in <module>
    lcd = HD44780()
  File "lcd3.py", line 15, in __init__
    GPIO.setup(self.pin_e, GPIO.OUT)
RuntimeError: No access to /dev/mem.  Try running as root!

Unfortunately /dev/mem does not exist. Could you please help?

Any ideas?

Firstly, what architecture are you targeting. Some architectures have the kernel symbol CONFIG_DEVMEM defined, some don't. If it's not defined, the device node won't exist. For example, my x86_64 router has a /dev/mem, however my WRT1200AC does not, because the kernel config option is not enabled. If it's not enabled, you'll need to create a new kernel with the relevant config option enabled.

Moving beyond the basics (lack of a CONFIG_DEVMEM=y in the kernel config is almost certainly why /dev/mem does not exist), why are you trying to write directly to /dev/mem? This is a pretty dangerous thing to do unless you know exactly what you're doing.

On devices with CONFIG_DEVMEM enabled, OpenWrt kernel is compiled with CONFIG_STRICT_DEVMEM. Quoting directly from the manpage

So even if it IS enabled, you may not be able to write to it in the way you desire.

Thank you for your response.
I try to run Python module RPi.GPIO (https://pypi.python.org/pypi/RPi.GPIO) on Raspberry Pi with OpenWRT from trunk.
RPi.GPIO has been installed using setup.py script, everything works fine until I run script.
The goal is to use HD44780 alphanumeric LCD connected to RPi's GPIO.

I will try with rebuilding kernel for my OpenWRT on RPi. Could you tell if I can do it using make menuconfig?

Do you know where this option is in make kernel_menuconfig ?

An easy way to find where a symbol is located in the menuconfig hierarchy is, fro the source directory

 find . -name Kconfig | xargs grep DEVMEM
./drivers/char/Kconfig:config DEVMEM

So, as you can see, CONFIG_DEVMEM is under Device Drivers-->Character Devices