SPI signal distorted at high speed

[JCAeron]

Two STM32H743 series MCUs are on a single board and they communicate using SPI. When SPI clock frequency is more than 1.5 Mhz, SPI communication is not working properly. The distorted clock signal waveforms at high frequencies are attached below.

A 51E series resistor is connected on all 4 signals.

The trace length is almost 35mm

I tried reducing the series resistors from 51E to 33E and 20E. No much difference was observed in the waveforms. What can be done? 

1. CLK freq = 1.5MHz

2. CLK freq = 3.125MHz 

3. CLK freq = 6.25MHz

4. CLK freq = 12MHz

[waclawek.jan]

Set the SPI's CLK and MOSI (and MISO in slave) pins to higher speed on their respective GPIO_OSPEEDR register fields.

JW

[AScha.3]

Yes, set pin speed in Cube -> very high , as @waclawek.jan  said.

And your probe (-> DSO) set to 10:1 ? ( otherwise probe cap. load too high .)

[JCAeron]

Please see the attached image. That seems to be already done.