How to display image on LCD using Frame buffer in Sitara AM335X.

Pankil Shah

Expert 1040 points

Other Parts Discussed in Thread: AM3358

Hi,

We are using AM3358 Sitara EVM and need to display various customized images on LCD.

From different forums found out that images in raw format can be written on /dev/fb0 (i.e. cat image.rgb > /dev/fb0).

Tried out that thing and its displayed also properly.

But, Need to know that how many format (RGB,YUV) and its variants (RGB888,BGRA,....) are supported with frame buffer?

Also any demo application or sample example are available for display module in RDK or SDK?

Thanks in advance.

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi,

Data from the framebuffer is directly fed to the AM335X LCD controller. Assuming that you are working in raster mode, framebuffer data must be in RGB format. The LCD controller does not do any processing. Any image that's not in RGB format must be processed by software before it's written to the framebuffer. You can check this tutorial for additional information: 6545.LCDC.pdf

0 Pankil Shah over 10 years ago in reply to Biser Gatchev-XID

Expert 1040 points

Hi Biser,

Thanks for your quick reply.

In SDK or RDK any sample application or demos are available for display?

Thanks.

0 Biser Gatchev-XID over 10 years ago in reply to Pankil Shah

TI__Guru**** 393215 points

I'm not a SW expert, but this information should be included in the Software Manifest on the SDK download page: http://software-dl.ti.com/sitara_linux/esd/processor-sdk/PROCESSOR-SDK-LINUX-AM335X/latest/index_FDS.html

0 Pankil Shah over 10 years ago in reply to Biser Gatchev-XID

Expert 1040 points

Hi Biser,
Thanks again.
Some more queries :
1. Frame buffer's color space can be changed in run time in am335x?
2. How to change width and height of resolution of frame buffer in kernel? In kernel, which files need to be changed?
Thanks.

0 Georgi Karpov over 10 years ago in reply to Pankil Shah

Expert 1185 points

Hi,

framebuffer colorspace can be changed using fbset command with -nonstd option.
Resolution also can be changed using fbset.

Also refer here:
www.kernel.org/.../framebuffer.txt

BR,
Georgi

0 Pankil Shah over 10 years ago in reply to Georgi Karpov

Expert 1040 points

Hi Georgi,
Thanks for your reply.
For setting up RGB888 mode, I have fired command "fbset -a -nonstd 1 -depth 24 -rgba 8/0,8/8,8/16,0/0".
And my fbset command show me this output :
mode "480x272"
geometry 480 272 480 816 24
timings 0 0 0 0 0 0 0
nonstd 1
accel true
rgba 8/16,8/8,8/0,0/0
endmode

Now I am writing RGB888 file to framebuffer but it not displayed properly.
While displaying BGRA image displayed successfully (BGRA mode is configured from boot time).
Looks like it is not changing color mode in run time with this command.

Regards.

0 Georgi Karpov over 10 years ago in reply to Pankil Shah

Expert 1185 points

Hi,

Have you tried to run fbset command before X server start?
What is not displayed properly for RGB888 ?

BR,
Georgi

0 Pankil Shah over 10 years ago in reply to Georgi Karpov

Expert 1040 points

Hi,

No, actually XServer is not running.

I tried to display RGB888 image on framebuffer. I wrote whole RGB888 image on FrameBuffer Port.

But that was not displayed properly on LCD. Image's part was duplicated and overlapped on display.

Thanks.

0 Georgi Karpov over 10 years ago in reply to Pankil Shah

Expert 1185 points

Try it with
fbset -a -nonstd 1 -depth 32 -rgba 8/0,8/8,8/16,8/32

fbset uses RGBA color space:
en.wikipedia.org/.../RGBA_color_space

BR,
Georgi

0 Pankil Shah over 10 years ago in reply to Georgi Karpov

Expert 1040 points

Hi,

Thanks for your reply.

But If I want to display only RGB888 (24-bit) buffer on framebuffer, then it will be possible?

Or It would just support 32bit configuration (like RGBA, BGRA,etc.) and all?

Thanks.

0 Georgi Karpov over 10 years ago in reply to Pankil Shah

Expert 1185 points

Hi,
It will be possible, as you can see A component in RGBA is transparency and it has 0x00 value for RGB888.

Georgi

0 Pankil Shah over 10 years ago in reply to Pankil Shah

Expert 1040 points

Hi,

Thanks for your valuable reply Georgi.

But in my case I have to write only RGB888 file to frame buffer. In case of RGBA, I can follow your suggestion but for that have to decode file in RGBA format which require more space on filesystem. In my case have to avoid this extra space formula.

I need to only write RGB888 file and need to set this format in Kernel /application(if supported).

Can you please guide me for configuring this.

Thanks.

0 Pankil Shah over 10 years ago in reply to Pankil Shah

Expert 1040 points

Hi,

I have updated the dts file and in LCD filed, changed bpp from 32 to 24.

And it started displayed 24 bits images properly, But the thing is it taking currently BGR24 format images.

@TI guys, Any suggested changes/addition in kernel, so that it would take RGB24 format also?

Thanks in advance.

0 Pankil Shah over 9 years ago in reply to Pankil Shah

Expert 1040 points

Hi,

Just to give update that can help any other.

If you change bpp in dts file from 32 to 24 than RGB888 color format will be set.

But as per errata of AM335x (http://www.ti.com/lit/er/sprz360f/sprz360f.pdf)

"The blue and red color assignments to the LCD data pins are reversed when operating in RGB888 (24bpp) mode compared to RGB565 (16bpp) mode."

As mentioned above BGR24 image was working fine while RGB24 was not that because of this above errata point.

So if you will write BGR24 image to framebuffer then it will display in RGB24 format on LCD. And that worked for me.

Thanks.

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How to display image on LCD using Frame buffer in Sitara AM335X.