Issues with FPS and Screen Tearing When Switching to Higher Resolution and Color Depth on STM32F7

Question

Hello Embedded Wizard Community!

In our project using STM32F7, we need to transition from a 24-bit color depth at 480x272 resolution to 24-bit 800x480 resolution. When I set the project to RGB888 800x480 settings and build it, I observe that the FPS drops to around 25. When I try to increase the FPS by making different settings (e.g., increasing LCDCLK), tearing starts to occur on the screen along with the increase in FPS.

Thinking that the problem might be hardware-related, I loaded the Graphics Accelerator example to validate the hardware and observed the same results. I then switched from RGB888 to RGB565 color depth and built the EW project, observing that the FPS increased from around 25 to 65 at 800x480 resolution. There might be a hardware issue here, but I also want to observe our main project at RGB565 color depth. However, when I tried to build the EW project with RGB565 settings, it seems the license doesn't allow it. Do we need to add something specific to try this setting in RGB565? Is it possible to change the RGB settings in ST's project code and try it out?

Answer 1

Hello,

depending on the target and the MCU speed, it might happen that there is not enough memory bandwidth so that you can update the entire screen in 800x480 with RGB888. As a result the effective framerate drops down.

Furthermore, please take care that the framebuffer width should be a multiple of 64 bytes. This means, the framebuffer width (in ewconfig.h) should be set to 832. Further details about the maximum pixel clock frequency depending on color format, framebuffer size and CPU clock speed can be found in the application note AN4861 from ST.

In case you want to change the color format of your license, please get in contact with us via contact@embedded-wizard.de

Best regards,

Manfred.

Comments

Hello Manfred,

Thank you for your prompt response and valuable insights. Your explanation regarding the memory bandwidth and framebuffer width considerations makes perfect sense and aligns with the issues we've been experiencing.

I will definitely take your advice and delve into the details provided in AN4861 from ST to better understand the maximum pixel clock frequency based on color format, framebuffer size, and CPU clock speed.

Regarding the color format change for our license, I will reach out to you via e-mail.

Once again, I appreciate your assistance..

Best regards,

Burak Cebesoy