Output frame buffer resolution

Andrew Poole

I apologise if this question has been answered before.

I would like to know how I can change the resolution of the video output at runtime. I have a graphics application, which uses OpenVG and outputs the rendered graphics to an EGL Window Surface. This is then output to a LCD panel that uses a custom driver. I would like to be able to create a simple function in my application that can change the output display resolution.

In my display panel driver, the x_res and y_res fields of the omap_video_timings structure are currently set to a default of 640x480, which will need to be changed later on in the application to an arbitrary resolution (to 1280x720 for example). How can I do this?

Thanks very much,

Andy

over 14 years ago

0 Steve Clynes over 14 years ago

TI__Mastermind 43875 points

Andy,

Have a look at the following Wiki pages.

http://processors.wiki.ti.com/index.php/Display_Subsystem

http://processors.wiki.ti.com/index.php/Adding_new_DVI_resolutions

http://processors.wiki.ti.com/index.php/UserGuideDisplayDrivers_PSP_03.00.00.05

BR,

Steve

0 Andrew Poole over 14 years ago in reply to Steve Clynes

Intellectual 570 points

Hi Steve,

Thank you for the links. I have read through the documentation and I am having no luck in changing the resolution.

When reading the documentation, the useful functions appeared to be:

Disabling the overlay and display
Calling 'fbset' with the desired resolution
Writing the desired resolution to /sys/class/graphics/fb0/virtual_size
Writing display timings to /sys/devices/platform/omapdss/display0/timings
Enabling the overlay and display

I have tried the above on the beagleboard for testing with no success. Is there any help you can give? Maybe any example code to show how this can be achieved from a linux application?

Thanks,

Andy

0 Punya Prakash over 14 years ago in reply to Andrew Poole

TI__Intellectual 1665 points

Andy,

SYSFS interface can be used to configure the DSS pipeline dynamically, for example you can set the final display device timings using the following command:

echo "<pixel_clock>,<xres/hfp/hbp/hsw>,<yres/vfp/vbp/vsw>" > /sys/devices/platform/omapdss/displayX/timings

Now if you want to configure the fbdev framework using fbset you would need to ensure that the source code supports the resolution you require. If the resolution is not supported, even if you try to pass the configuration to the driver it will fall back to the default resolution. Please look at /drivers/video/modedb.c file and modify it according to your requirements.

If you would like to test this with the currently supported parameters please use this example as a reference:

echo 0 > /sys/devices/platform/omapdss/display0/enabled
# Configure framebuffer timings, this resolution is defined in modedb.c file
fbset -fb /dev/fb0 -xres 640 -yres 480
# Set manager0 to dvi display
echo "dvi" > /sys/devices/platform/omapdss/manager0/display
# Enable display2
echo 1 > /sys/devices/platform/omapdss/display2/enabled
# If needed display device timings can be set, for example to set display timings to 720P
echo "72428,1280/190/120/32,720/13/3/5" > /sys/devices/platform/omapdss/display2/timings

Regards, Punya
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0 Andrew Poole over 14 years ago in reply to Punya Prakash

Intellectual 570 points

Hi Punya,

Thank you for the help, I had actually got this far and so it is nice to see I am doing the right thing. I believe that the steps that I am doing are changing the resolution in some way as the console output on the monitor looks larger or smaller depending on the resolution.

I am starting Linux with the bootargs "...omapfb.mode=dvi:1024x768MR-24@60", which gives the following setup:

fbset
mode "1024x768-60"
   # D: 56.000 MHz, H: 47.298 kHz, V: 59.870 Hz
   geometry 1024 768 1024 768 32
   timings 17857 80 48 3 15 32 4
   accel false
   rgba 8/16,8/8,8/0,0/0
endmode
cat /sys/devices/platform/omapdss/display0/timings
56000,1024/80/48/32,768/3/15/4
cat /sys/class/graphics/fb0/virtual_size
1024,768

Now if I perform these steps...

echo 0 > /sys/devices/platform/omapdss/display0/enabled
fbset -fb /dev/fb0 -xres 800 -yres 600 -vxres 800 -vyres 600
echo 1 > /sys/devices/platform/omapdss/display0/enabled
echo "35500,800/80/48/32,600/3/11/4" > /sys/devices/platform/omapdss/display0/timings
echo "800,600" > /sys/class/graphics/fb0/virtual_size

the resolution looks as though it has successfully changed:

fbset
mode "800x600-60"
   # D: 35.500 MHz, H: 36.979 kHz, V: 59.837 Hz
   geometry 800 600 800 600 32
   timings 28169 80 48 3 11 32 4
   accel false
   rgba 8/16,8/8,8/0,0/0
endmode

However, when I now run my graphics application, the EGL libraries still thinks the resolution is 1024x768, not 800x600. I.e. eglQuerySurface returns a width and height of 1024 and 768 respectively. Which is where the problem lies.

Also, very strangely, I cannot return back to the original resolution of 1024x768. If I perform the following steps...

echo 0 > /sys/devices/platform/omapdss/display0/enabled
fbset -fb /dev/fb0 -xres 1024 -yres 768 -vxres 1024 -vyres 768
echo 1 > /sys/devices/platform/omapdss/display0/enabled
echo "56000,1024/80/48/32,768/3/15/4" > /sys/devices/platform/omapdss/display0/timings
echo "1024,768" > /sys/class/graphics/fb0/virtual_size

The resolution has not successfully changed:

fbset
mode "800x600-94"
   # D: 56.000 MHz, H: 58.334 kHz, V: 93.784 Hz
   geometry 800 600 1024 768 32
   timings 17857 80 48 3 15 32 4
   accel false
   rgba 8/16,8/8,8/0,0/0
endmode

I should also point out that setting the resolution from the bootargs works fine, however this is unsuitable for my application.

Thanks,

Andy

0 Andrew Poole over 14 years ago in reply to Andrew Poole

Intellectual 570 points

Further to my last post, I have been able successfully return the resolution back to its original set up:

Andrew Poole said:

Also, very strangely, I cannot return back to the original resolution of 1024x768. If I perform the following steps...

echo 0 > /sys/devices/platform/omapdss/display0/enabled

fbset -fb /dev/fb0 -xres 1024 -yres 768 -vxres 1024 -vyres 768

echo 1 > /sys/devices/platform/omapdss/display0/enabled

echo "56000,1024/80/48/32,768/3/15/4" > /sys/devices/platform/omapdss/display0/timings

echo "1024,768" > /sys/class/graphics/fb0/virtual_size

The resolution has not successfully changed:

fbset
mode "800x600-94"
   # D: 56.000 MHz, H: 58.334 kHz, V: 93.784 Hz
   geometry 800 600 1024 768 32
   timings 17857 80 48 3 15 32 4
   accel false
   rgba 8/16,8/8,8/0,0/0
endmode

I found that the fbset '-n' option was needed to change the video mode immediately. So step 2 in the above quote becomes:

fbset -n -fb /dev/fb0 -xres 1024 -yres 768
(setting the virtual resolution here has no effect)

I still can't solve the main issue with my graphics application not detecting the new video resolution. I am assuming that the function 'eglCreateWindowSurface' reads the resolution from somewhere but as there is no useful documentation nor any source code, I can't tell where it reads it from. Does anyone have any idea how to get an EGL based Graphics application to detect a correct screen resolution?

Thanks

0 imtiyaj over 14 years ago in reply to Andrew Poole

Prodigy 240 points

HI Andy!

I am unable to change back the resolution to Original one, once I change it. Where did you get the fbset utility from?

The "fbset" utility I am using, does not have any '-n' option. I am using the utility from here ftp://ftp.scw.net.br/pub/slamd64/slamd64-12.2/source/a/bin/fbset-2.1.tar.gz.

One thing that I am not able to understand is that why

fbset -fb /dev/fb0 -xres $w -yres $h -vxres $w -vyres $h alone is not able to change  the resolution.

Thanks in advance,

regards

-Nitin

0 Andrew Poole over 14 years ago in reply to imtiyaj

Intellectual 570 points

Hi Nitin,

I was using quite an older version of the Angstrom distribution (2009 stable) for the Beagleboard for testing, which had a version of fbset that supported the '-n' or '--now' option. I have since moved onto my target hardware which uses the Arago distribution from the latest TI PSP and this no longer has the '-n' option.

I now have no ideas on how to change the resolution at runtime for either Linux or a graphics application that uses the SGX.

Andy

0 imtiyaj over 14 years ago in reply to Andrew Poole

Prodigy 240 points

HI Andy,

I checked in the code for fbset v 2.1, it will immediately apply the settings if you have not given the 'test' option.

I was trying to change the GFX overlay from TV(720x480) to LCD(1024x768) I have a VGA monitor as a display on this path. I am using 2.6.32 omap-linux kernel, nothing from PSP.

I used this procedure

ln -s /dev/graphics/fb0 /dev/fb0
fbset
echo 0 > /sys/devices/platform/omapdss/overlay0/enabled
echo "" > /sys/devices/platform/omapdss/overlay0/manager
echo 0 > /sys/devices/platform/omapdss/display1/enabled
echo "64800,1024/44/116/156,768/3/29/6" > /sys/devices/platform/omapdss/display0/timings
echo "1024,768" > /sys/class/graphics/fb0/virtual_size
fbset -fb /dev/fb0 -xres 1024 -yres 768
echo "lcd" > /sys/devices/platform/omapdss/overlay0/manager
echo 1 > /sys/devices/platform/omapdss/display0/enabled
echo 1 > /sys/devices/platform/omapdss/overlay0/enabled

And I am not able to see the new resolution on LCD, it has retained the old one. Can anybody suggest what might be going wrong here?

But if I used following commands to change resolution to 1024x768 from 800x600, if by default the kernel command-line asked to boot in "dvi"

# echo 0 > /sys/devices/platform/omapdss/display0/enabled
# echo "64800,1024/44/116/156,768/3/29/6" > /sys/devices/platform/omapdss/display0/timings
# echo "1024,768" > /sys/class/graphics/fb0/virtual_size
# fbset -fb /dev/fb0 -xres 1024 -yres 768
# echo 1 > /sys/devices/platform/omapdss/display0/enabled

I am able to change the resolution successfully.

regards

-Nitin

0 Andrew Poole over 14 years ago in reply to imtiyaj

Intellectual 570 points

Hi Nitin,

I can confirm that, running on my distribution of Linux (based on a 2.6.36 OMAP-Linux Kernel), fbset is at version 2.1 and now that I have my framebuffer working correctly the settings are immediately applied.

Something that I have noticed is that the pvrsrvkm kernel module reads the framebuffer resolution only once at the time the module is loaded. This is what is causing the eglCreateWindowSurface to create a surface with the wrong resolution. Reloading the module ('/etc/init.d/rc.pvr restart') will re-read the framebuffer resolution and allow a graphics application to render to the correct size.

However this really isn't ideal as it requires the application to release its graphics context and clean up before reloading the pvrsrvkm kernel module, only to then recreate the graphics context and egl window surface for the application to function correctly. I really hope that someone knows a nicer way to do this?!

Your situation with changing from TV to LCD is a strange one... maybe reloading the kernel module after the call to fbset may help for you too.

Regards,

Andy

0 Andrew Poole over 14 years ago in reply to Andrew Poole

Intellectual 570 points

Does anyone have any ideas how to change the resolution without having to destroy the EGL graphics context and then reload the pvrsrvkm kernel module? Destroying the graphics context means that all my textures/colours/paths have to be recreated.

Andy

0 Prabindh Sundareson over 14 years ago in reply to Andrew Poole

TI__Expert 6580 points

Graphics vertex/fill calculations related to rendering - are relative to the current screen resolution. Also the line width of the buffer changes. In any case, even if it were theoretically possible to keep the same driver, the context still needs to be re-created.

One possible suggestion is to load the textures in physical memory to avoid re-loading time if they are large.

Another suggestion could be to always allocate the larger framebuffer, and play with Viewports to position your drawing appropriately.

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Output frame buffer resolution