Using 1280x800 HDMI resolution with BBB

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gschroeder81
 
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Using 1280x800 HDMI resolution with BBB

Post by gschroeder81 »

Hello, I have a question about using the 7" 1280x800 IPS LCD (http://www.adafruit.com/product/1726) screen with the BeagleBone Black.
The LCD's native 1280x800 resolution is not included in the standard list of supported HDMI resolutions for the BeagleBone Black. See this page. (http://elinux.org/Beagleboard:BeagleBoneBlack_HDMI)

I don't believe that there is even support for any resolutions with the 10:6 aspect ratio of this LCD. Is there some work around? I have read through all the discussions on the Adafruit forums about this, and everything I could find on the net regarding forcing resolutions. I can find no specific information that says that anybody has gotten that resolution to display correctly. I know that we can run with 1280x720, but that will result in a unacceptably skewed image. This is for an avionics project and we need images to maintain their proportionate integrity.

Has anybody figured out how to get that resolution to work with the BBB?
Thanks,

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adafruit2
 
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Re: Using 1280x800 HDMI resolution with BBB

Post by adafruit2 »

This is more of an OS question, since thats what chooses the resolution. Linux tends to do its best to match the best resolution with similar aspect ratio - it'll probably go with 1280x768@60 and have black bars on the sides. you should adjust your linux OS install to force the desired resolution (just like you do in Windows when you can change the resolution of the monitor)
We don't have it set up on a BBB right now to measure the skew or black bars so we can't guarantee the results you want

it sounds like you need a precision display, and we dont have one with 1280x768@60 in stock so you may want to try to find & purchase a monitor with that exact native resolution!

gschroeder81
 
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Re: Using 1280x800 HDMI resolution with BBB

Post by gschroeder81 »

What I am referring to is a hardware limitation of the HDMI chip on the BBB. The page I linked to does not specify an OS, but rather a board capability, unless I am mistaken. We are building our own bare metal OS, so if it was possible from a hardware standpoint the OS wouldn't be the limiting factor.
Following are the supported resolutions of the BeagleBone Black. You display may not support all of these resolutions on the board.
1920x1080@24 (Audio)
1324x768@60
1280x768@60
1280x1024@60
1280x720@60 (Audio)
1152x864@75
1024x768@76
1024x758@60
800x600@60
800x600@75
640x480@75
It is possible to force a resolution to be used by the board. The availble resolutions will however, be limited to those that have been determined to work by the DRM manager on the board. As a result, not all resolutions that can be supported by the display are available.
I do have access to a 1280x800 LCD that I have worked with, and using Debian, I can set several display resolutions using xrandr commands, but it will not accept the 1280x800 resolution when I specify it. It just says that the resolution "is not found". Also, when I specify the custom resolution in the uEnv.txt file, it ignores that resolution command. I am still searching for a way to force that resolution through the kernel.

I have searched for a similar quality LCD in the preferred 1024x768 resolution and I haven't found anything so far. I am sure that they exist, but it must be an open frame LCD and must have a wide omni-directional viewing angle.
Thanks for the interest,

gschroeder81
 
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Joined: Tue Apr 22, 2014 5:59 pm

Re: Using 1280x800 HDMI resolution with BBB

Post by gschroeder81 »

Okay, I finally figured out a way to get the BBB to display the correct resolution and it is now outputting 1280x800@60 over HDMI. It's relatively simple once you figure out that not all Linux distros respect the changes made to kernel configurations during boot. Most people will know that you can force a resolution by setting it in the eEnv.txt using the following command: <kms_force_mode=video=HDMI-A-1:1280x800M@60> but what is not obvious is that apparently most of the common distros of Angstrom and Debian ignore those changes when they boot and revert to their own best judgement for HDMI output, rendering your changes ineffective past the initial splash screen.

Also I wasted a lot of time trying the different "xrandr" commands, and although they are helpful in finding out the current resolution and setting different "supported" resolutions from within the desktop environment, xrandr will not let you set an "unsupported" resolution.

I finally tried Robert Nelson's linux images from http://rcn-ee.net/deb/rootfs/wheezy/ and although I can't confirm that all of them work with this arrangement, the one I tried did honor the changes made to kernel via uEnv.txt modification and didn't reset the HDMI upon bootup. If you use the images that I linked to you will have to install the desktop environment via the instructions here or similar. http://elinux.org/Beagleboard:Installing_LXDE

So, in conclusion, the BBB does support the 1280x800 resolution, but not with standard linux distributions such as the ones from Beagleboard.org. Neither is there any good documentation on the subject that I could find. Hopefully this can help somebody else.

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adafruit_support_mike
 
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Re: Using 1280x800 HDMI resolution with BBB

Post by adafruit_support_mike »

Thank you for posting what you found. I'm sure it will help someone else in the future.

In the meantime, I'm glad to hear you have it working. ;-)

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