Touchgfx 4.18 framebuffer pixel format does not match layer pixel format when selecting L8

[RMolins]

I am currently working with the STM32F769I-Eval Board and I want to use the LTDC only using the internal RAM with a 800*480 display with no internal RAM

To achieve this I want to have the frame buffer defined as L8_RGB888 to have a 800*480= 384kB + LUT, of the RAM dedicated to the frame buffer.

I have configured LTDC with

1. Display Type RGB888
2. Layer 0 pixel format to L8

However, when I try to configure the TouchGFX, Frame buffer pixel format can only be set to RGBA2222 (and variants). This creates a 8bpp LUT with equally distributed colors, i.e, only possible values are 0x00,0x55,0xAA, 0xFF, which kills the purpose of the the LUT.

Is it possible to really define a LUT and a frame buffer which uses this LUT? Or in other words, to set the Frame buffer pixel format from TouchGFX to L8_RGB888?

I am using:

• STM32 Cube vesrion 1.8
• STM32Cube MCU Packed for STM32F7 1.16.2
• X Cube-touchgfx.4.18.1

[Osman SOYKURT]

Hi RMolins,

Could you give more information about your configuration please ?

• Which firmware pack do you use ?
• Which version of TouchGFX Designer do you use ?
• Which version of STM32CubeMX do you use ?

Thanks,

/Osman

[RMolins]

I have added the requested version information.

About the configuration it is basically a blank project with TFBGA216 with RTOS CMSIS_V2 10.2.1, CRC enabled, and using TIM1 as clock source for RTOS. The issue/question I am finding is before opening TouchGFX Designer. The TouchGFX Designed is correctly showing the configuration selected in the STM32CubeIde and I am able to make the setup work with correct colors if using only a fraction of the screen

Regards,

[Osman SOYKURT · Accepted solution]

Hi RMolins,

I talked about your issue with my colleagues, the answer I got is that we don’t support L8 as the framebuffer format. Only as image format. The reason is that it is difficult to blend images in L8 mode. As you don’t have all the colors.

Regards,

/Osman

[RMolins]

Seems I will have to add external RAM to be able to store at least a full frame. Thank you for the support