imx8qm SPI using ADC pins clock looks bad

We need a 1.8V SPI bus, and we configured the device tree to use lpspi1 for this purpose, which is available according to the apalis imx8 datasheet. It’s using pins ADC_IN3, ADC_IN4, ADC_IN5 as Clock, MOSI, MISO, and ADC_IN6 as GPIO pin.for CS (pins 311, 315, 317, 319 from SOM, ALT1 function). Clock is running at 5MHz.

MOSI and CS signals look good, but the clock looks bad on the scope, is very shark-finny. Since we don’t have the schematic for the SOM, can you tell me what is connected between pins 311, 315, 317, 319 and the i.MX8QM that might be affecting the signals?

Pin 311 connected to SOC through 1K resistor as it described at chapter 5.21 Analogue Inputs of Apalis iMX8 datasheet. For pins 315, 317, 319 schematic please check chapter 5.20 Touch Panel Interface.

To improve signal quality you can try to increase pins’ drive strength.

Thank you!

You are welcome.