The noise of ADC get terrible after enabling SDRAM / LTDC

[HCui]

I am using STM32H753 for signal sampling.

I have enabled ADC1 and ADC3, both of which are in 16 bits scan mode （4 channels）.

Everything worked well until I enabled FMC / LTDC to migrate a UI application.

I noticed that most channels of ADC share IOs with FMC / LTDC. This may introduce noise into the ADC input when these peripherals are enabled at the same time.

If someone has encountered this problem?

[Uwe Bonnes]

The ADC related application notes give examples and possible workarounds with noise issues, but not w.r.t. SDRAM / LTDC. I am sure increase chip activity due to FMC / LTDC wil strongly influence noise. Supply lines also may be an attack vector for noise. Did you consider that vector?

[HCui]

Thanks. I found that the noise seems get reduced after I disabled the DMA 2D accelerator in the TouchGFX tab and keep the priority of ADC-DMA low. The noise level also relates to the sampling rate. It is really weird.

[HCui]

the analog domain and digital domain are seperated properly

[HCui · Accepted solution]

I think I have found the reason. It's the cache. ADC1 and ADC3 shared the same DMA buffer, and the sampling result of ADC1 should be overwritten by the ADC3's.​ However, some samples were not overwritten as expected （the CPU think they are not actually）, which makes the FFT result weird.

Note: The UI application is running on FreeRTOS, the MPU was disabled in RTOS configuration tab.