Altah
Posts: 5
Joined: Wed Jan 11, 2017 8:38 am

Edid with custom resolution not working

Wed Jan 11, 2017 9:00 am

I have a problem with a compute module in an embedded application. In this application, the compute module should drive an specific display, wich has a custom resolution. This resolution is not in the standard resolution list, so

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hdmi_group=1
or

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hdmi_group=2
doesn´t work.
For testing purposes i put in the good old

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hdmi_timings=<h_active_pixels> <h_sync_polarity <h_front_porch> <h_sync_pulse> <h_back_porch> <v_active_lines> <v_sync_polarity> <v_front_porch> <v_sync_pulse> <v_back_porch> <v_sync_offset_a> <v_sync_offset_b> <pixel_rep> <frame_rate> <interlaced> <pixel_freq> <aspect_ratio>
I filled it up with the parameters out of the display datasheet and it works fine!
Now i need to use Edid storage in the display driver.
I made my own edid file and programmed it with another compute module to the storage.
The edid file just contains the general settings and one detailed timing mode. In this i filled in the same data as in the

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hdmi_timings=...
If i read it back (with i2cdump e.g.) it is the correct data in the storage.
However, the screen remains white, wich means the timings are not correct or there is no display output from the Rpi (input).

If i build up an development envoirement to be able to access the compute module over ssh, is there any possibility to view something like a logfile to see, why it is not displaying the resolution described in the edid?

Has anybody experiance yet with custom resolutions in the edid?

I hope for mercy, as this is my first post and my english is bad.

dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5594
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Edid with custom resolution not working

Thu Jan 12, 2017 4:07 pm

We only support standard CEA and DMT resolutions from the EDID.
Other resolution need a config.txt setting.

Altah
Posts: 5
Joined: Wed Jan 11, 2017 8:38 am

Re: Edid with custom resolution not working

Thu Jan 12, 2017 4:25 pm

Thank you for your answer!
Is there any way to allow non-standard resolutions in EDID?
Or do i have to make a workaround like checking the EDID and the current setting automativally?
For example using a script after startup which edits the config.txt ,if the resolution is not matching and reboots the Rpi?

dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5594
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Edid with custom resolution not working

Thu Jan 12, 2017 5:09 pm

Altah wrote:Thank you for your answer!
Is there any way to allow non-standard resolutions in EDID?
Or do i have to make a workaround like checking the EDID and the current setting automativally?
For example using a script after startup which edits the config.txt ,if the resolution is not matching and reboots the Rpi?
That is what I'd suggest.

You could open an issue and link to a suitable EDID that doesn't behave how you'd desire.
Explain what hdmi timings you would expect to get and how you are determining that from the EDID.
As this is pretty niche I won't promise it will happen, but if there appears to be a straightforward solution without risking breaking existing users setups we will consider it.


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