framebuffer settings for koreader

Hello,
I wrote a small boot script that allows the user to choose at startup
the application to start up (nickel or koreader).
It shows two buttons on the screen (using pickle showpic) and
detects which button has been pressed (pickel wait-for-hit).
This procedure allows to avoid the boring procedure with the png image and
the need for a process to continuously monitor file access...
Now I can successfully start nickel normally, or start nickel and after some seconds
launch kobo_reader.sh.. it works.
However I would try to avoid to launch nickel to kill it afterwards,
so I tried to lauch directly kobo_reader.sh.
Something happens, because backlight turns on, but nothing appears
on the screen... the buttons disappear and only a completely white screen remains.
I tried to use the framebuffer rotate trick, but it didn't works.
What is needed to setup the frame buffer before to start koreader?
Thanks
Andrea