RE: [Ltib] Framebuffer problem with ltib-cf_nommu-20081215

[Anthony L. Montiel]

Hi Robert,

I've done some Framebuffer work - so I thought I'd give you my 2 cents.
However, I don't know anything about the mcf5329, so caveat-emptor...

The description of "shearing" stands out for me - I've seen that happen
in a number of different circumstances:
- I assume the embedded system isn't "loaded" very heavily - that can
  sometimes cause "shearing" or "tearing"
- Because you are running at a low resolution, most performance related
  issues can be ignored

Unfortunately, this leads me to think that there might be a discrepancy
between the driver and the hardware. There are a number of timing
parameters which might lead to this problem. I am assuming you are
running on custom hardware - not a reference design/Freescale dev system?

If this is the case, the good news is that it is easy to update the 
timing values for the driver. Again, I'm not sure if it holds for the
mcf5329, but for the i.MX the file to look at is:
   .../linux/drivers/video/mxc/mxcfb_modedb.c

I hope this helps in some small way...Regards,
Tony

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of
Stuart Hughes
Sent: Thursday, April 30, 2009 2:04 AM
To: address@hidden
Cc: address@hidden
Subject: Re: [Ltib] Framebuffer problem with ltib-cf_nommu-20081215

Hi Robert,

Have you tried running this test code on a PC (x86).  It it works on 
that as expected it would tend to imply there may be a problem with the 
hardware or driver for the mcf5329.  Once you've established that it's 
probably worth contacting Freescale as they'd have a platform to test 
on.  I'd be interested to hear what you find out.

Also once resolved, if you're willing we could put your updated kernel 
on the the public Savannah site.

Regards, Stuart

Robert S. Grimes wrote:
> I've been trying to get Microwindows/Nano-X to work with the BSP from
> Freescale, which features a kernel a bit newer than CVS for the mcf5329
> processor, and more importantly for me, supports 320 x 240 resolution
> LCD screens.  I had thought the hardware and framebuffer were working,
> but now I'm not so sure...
> 
> Attached is a silly test program that writes directly to the framebuffer
> - in other words, I'm not using Microwindows here.  Anyway, in
> pseudo-code the program looks like this:
> 
> test:
>   open framebuffer
>   write all zeros to it (i.e. erase the screen)
>   sleep(10) to allow inspection
>   lseek to beginning
>   write all ones to it (i.e. set all pixels white)
>   sleep(10)
>   lseek to beginning
>   write a pattern of 8x8 multi-colored boxes to screen
>   sleep(10)
>   close framebuffer
> 
> Running this shows a nice blank screen for 10 seconds, then a white
> screen for 10 seconds, then finally some pretty boxes.  Or at least,
> that is what is supposed to happen.
> 
> What actually happens, sometimes, is that, sometimes it works, other
> times the white screen shows the flicker/tearing/shearing throughout the
> entire lower two-thirds of the screen.  Of course, the black looks fine,
> but surprisingly, the colored blocks also looks fine.  Well, almost -
> when the white shows the shearing, there is usually a small black
> rectangle, maybe 3-4 pixels wide by 6-8 high, at the far left of the
> screen, centered vertically about the first sheared line; this block is
> also present on the white screen, along with an 6-8-pixel long vertical
> black line at the same elevation, midway across the screen.  I don't
> know if that little line shows up with the colored boxes.
> 
> I don't thing there is anything wrong with my code - it's so simple -
> but perhaps I'm missing something?  So it seems to be a framebuffer (or
> hardware, of course) problem.  Any ideas?
> 
> I don't have any familiarity with the framebuffer driver, so just
> jumping in is a bit daunting; can anyone point me to a good introduction
> on it, or give me a few pointers? 
> 
> Thanks,
> -Bob
> 
> P.S. I've also posted this on the Microwindows mailing list, because I
> had been discussing this problem there before, when I thought it was a
> Microwindows problem - please forgive me if you've run into this posting
> before...
> 
> 
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> 
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