Hi Ohm - I'm a newb here too but been messing with gumstix and LCDs for
a few weeks. I'm having success with the Sony LCD thanks to the wiki docs.
A few points - try dd if=/dev/fb0 of=/dev/null :) if being the input
file and of the output file.
the command as you typed it will send zeros to the fb until its full
which gave you the no space left error (and would blank the screen). At
least the fb exists and accepts input. This way round it should dump all
of /dev/fb0 to null without error and report a count of bytes (or kb or
some indication of filesize).
Nothing on your LCLK and FCLK and the dmesg output means the kernel
isn't setting those up - you need to give some values in the bootargs
(and I suggest using them rather than pxaregs - more human readable)
Have a look at the file pxafb.txt in the kernel source Documentation/fb/
directory for some more info on using the bootargs. You set the PIXCLOCK
in picoseconds then I think the other values are derived from that ie
the HSYNCLEN will be x number of pixclock periods as will left and right.
It's pretty tough figuring these values even with a good datasheet, pity
the ALPS datasheet doesn't have timing data :(
Also in an earlier post Mark was asking for easy ways to get a picture
on the screen so you know there's something there.
I suggest that anyone playing with LCD setups when compiling your kernel
for framebuffer support make sure to also:
enable Virtual terminal in Character Devices
+ support for console on virtual terminal
then in Graphics Support --> Console display driver support
enable Framebuffer Console support
and Select compiled-in fonts
eg VGA 8x16 font
then add 'console=tty0' to your bootargs in front of
'console=ttyS0,115200n8' so for example my bootargs look like this for
the Sony LCD:
setenv bootargs console=tty0 console=ttyS0,115200n8 root=1f02
this way you get the nice little penguin and kernel messages on screen
as soon as the kernel initializes and even if things look wrong you know
you're on track.
So good luck with the ALPS screen I'm sure you'll get there, I hope this
info helps a little
>I am working alongside Mark on this ALPS project. I
>just needed to ask a few newb questions.
>1) How do we know the size of fb0 and if it has been
>set up correctly? I get this with ls -l in /dev/:
>crw-r----- 1 root tty 29, 0 Nov 7 2005 fb0
>It gives me the major and minor numbers, which is
>correct, i think, since it is a special file. How can
>I find how big the device file is?
>Further, Mr. Jim Walters suggested using dd
>if=/dev/zero of=/dev/fb0 to get a read on how much
>memory is allocated to fb0:
># dd if=/dev/zero of=/dev/fb0
>dd: /dev/fb0: No space left on device
>2) I used an oscilloscope to find initial frequencies.
>can this be connected to this dmesg output?
>-- pxa2xx-fb pxa2xx-fb: overriding resolution: 240x320
>-- pxa2xx-fb pxa2xx-fb: overriding bit depth: 8
>-- PXA: invalid hsync_len 0
>-- PXA: invalid left_margin 0
>-- PXA: invalid right_margin 0
>-- PXA: invalid vsync_len 0
>(edit before sending: i set the h and vsync_len and
>margin values to values other than zero, and still no
>What would cause L_FCLK to not be outputting a
>What can I do to put out a frequency?
>3) Holly Gates mentioned this in a response to Mark:
>HSW, BLW, and ELW to about 1uS.
>if i were to do this using pxaregs, would the usage
>root/pxaregs LCCR1_HSW 1 ?
>if i were to do it in the bootargs, would the usage
>... video=pxafb:mode:240x160-8,passive,hsynclen:1 ...
>Specifically, what are the units when using pxaregs
>and when using the command line?
>Thank you very much, we'll all get this ALPS display