gtn
Posts: 5
Joined: Sat Oct 12, 2013 11:26 am

Can I use a 4.3" LCD with Pi?

Sat Oct 12, 2013 1:26 pm

We are a group of hobbyists trying to use Pi for an automation project.

We planned for a 4.3" / 5 " display and working on converting HDMI to RGB which is moving smoothly. Our converter can supply EDID information.

But now we are wondering why X running on Pi is not looking at EDID at all. If X is not looking at it, how can I statically convey to X my display physical size and resolution?

Will Pi Graphics chip support 480 x 272 resolution ? I assume since Pi can run at HD resolution, producing a lower resolution should not be a problem. Am I right or wrong?

Thanks in advance for any help.

texy
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Location: Berkshire, England

Re: Can I use a 4.3" LCD with Pi?

Sat Oct 12, 2013 2:06 pm

Hi,
I cant answer the EDID question, but certainly X on the Pi can support lower resolutions - I can run X on my 2.8" TFT using 320 x 240 resolution.
Of course you are restricted to what you can do with that resolution, but it is still very usable :
Image

Texy
Various male/female 40- and 26-way GPIO header for sale here ( IDEAL FOR YOUR PiZero ):
https://www.raspberrypi.org/forums/viewtopic.php?f=93&t=147682#p971555

karlkiste
Posts: 189
Joined: Tue Jan 22, 2013 8:50 am
Location: berlin, germany

Re: Can I use a 4.3" LCD with Pi?

Mon Oct 14, 2013 8:53 am

The good thing is, you don't need EDID on the pi, you can set a fixed resolution in config.txt. This is most useful when the pi is hard-wired to a certain display.

When booting, the kernel sets a framebuffer graphics mode (the pi has no native text modes afaik). X will just use that mode, it will not set a new mode. Therefore, X does not need to read EDID. Depending on the settings in config.txt, the bootcode will or will not read and act upon EDID data.

I'd like to do similar things, so... :-) How do you convert to RGB? Do you also have a solution for converting to LVDS?

Greets,
Kiste

gtn
Posts: 5
Joined: Sat Oct 12, 2013 11:26 am

Re: Can I use a 4.3" LCD with Pi?

Mon Oct 14, 2013 11:22 am

I answer second question first, I am working on the hdmi to RGB converter.

Right now,I am not with my RPi, so what I have read up in the day is yet to be confirmed. But combining whatever I have read up on, I have strung together following hypothesis on RPi's work.

1. The binary blob of boot-loader seem to read EDID over HDMI link. If not overridden by config.txt, HDMI detects device connection through hot_plug and tries to read EDID from device.
2. Assuming EDID is read, it will configure the HDMI output to suit the device and loads Linux kernel.
3. If X is setup to run, X detects fb driver and through the framebuffer deciphers mode line and configures itself. I want to check if fbdev is set as default driver in xorg.conf.

The standard CEA and DMT modes do not list my LCD panel which is 4.3" with 480 x 272 resolution. So, I need EDID or some way of tailoring HDMI output to my LCD size and resolution.

I also have seen in forums that EDID can be supplied via a file and a parameter in config.txt. Also, there is a discussion,

http://www.raspberrypi.org/phpBB3/viewt ... 29&t=24679

which mentions setting hdmi_cvt parameter in config.txt. I will try over next week in my spare time.

gtn
Posts: 5
Joined: Sat Oct 12, 2013 11:26 am

Re: Can I use a 4.3" LCD with Pi?

Mon Oct 14, 2013 11:29 am

texy wrote:Hi,
I cant answer the EDID question, but certainly X on the Pi can support lower resolutions - I can run X on my 2.8" TFT using 320 x 240 resolution.
Of course you are restricted to what you can do with that resolution, but it is still very usable :
Texy
I think I have got to know how to supply EDID. I need EDID as I am using HDMI output and my LCD panel is 4.3". I hope I have got answer to what I was looking for.
Your suggested route is interesting if only I had looked for it earlier. Now I have travelled quite a distance in the direction I have and if this reaches dead end, I may have to follow your route.

Thanks,
gtn

gtn
Posts: 5
Joined: Sat Oct 12, 2013 11:26 am

Re: Can I use a 4.3" LCD with Pi?

Mon Oct 14, 2013 11:35 am

karlkiste wrote:
I'd like to do similar things, so... :-) How do you convert to RGB? Do you also have a solution for converting to LVDS?

Greets,
Kiste
Hi,

If and when my current attempt is successful, I want to do HDMI to LVDS conversion too.

Thanks,
GTN

karlkiste
Posts: 189
Joined: Tue Jan 22, 2013 8:50 am
Location: berlin, germany

Re: Can I use a 4.3" LCD with Pi?

Mon Oct 14, 2013 11:49 am

Argh... Sorry. Shortcut-posting. You've already found the link I had given again ;-) So, to reduce confusion, I edit this nonsense post.

Greets,
Kiste

gtn
Posts: 5
Joined: Sat Oct 12, 2013 11:26 am

Re: Can I use a 4.3" LCD with Pi?

Mon Oct 14, 2013 12:47 pm

No,

That is reserved for spare time over this week. :)

Thx,

GTN

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