Accessing LCD controller registers

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brian_
Posts: 15
Joined: Mon Jan 09, 2017 11:59 am

Accessing LCD controller registers

Fri Jun 23, 2017 5:16 pm

Hi,

I am using your SAMA5D4 Xplained evaluation kit and am interested in altering some of the settings of the LCD display I have connected.

On the board, I am running an embedded Linux OS based on the poky-atmel Yocto build (krogoth branch).

The settings I am interested in altering are the chromium and luminance settings.

From the datasheet, I can see that these settings are found in the following registers; LCDC_HEOCFG14, LCDC_HEOCFG15 and LCDC_HEOCFG16.

If I understand correctly, these registers should be memory mapped.

I have tried accessing the registers using the devmem2 utility. I.e.

# /usr/bin/devmem2 0xF00003C4 word 0x7FFFFFFF

Which should set CSCRY, CSCRU and CSCRV coefficients of the color space matrix to -4. However there is no noticeable visual difference on my LCD display.

I am wondering if there is something that I am doing wrong and/or have missed out.

Thanks in advance.
blue_z
Location: USA
Posts: 1560
Joined: Thu Apr 19, 2007 10:15 pm

Re: Accessing LCD controller registers

Mon Jun 26, 2017 8:23 pm

brian_ wrote:The settings I am interested in altering are the chromium and luminance settings.

From the datasheet, I can see that these settings are found in the following registers; LCDC_HEOCFG14, LCDC_HEOCFG15 and LCDC_HEOCFG16.
There's much more to luminance and chrominance (note proper spelling) than those three registers.
brian_ wrote:Which should set CSCRY, CSCRU and CSCRV coefficients of the color space matrix to -4. However there is no noticeable visual difference on my LCD display.
There are several possible obvious reasons.
Maybe you didn't change the value of the register. Did you read it before and after?
Are you displaying anything from the high-end overlay?
Maybe the HEO is not in YUV mode.

Regards

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