I am using STM32F303 and initialize SPI1 as Master. My microcontroller supports SPI frequency up to 18 MHz. But at 9 MHz, SCK signal is already triangle waveform, while MOSI signal is normal waveform. SCK pin is initialized with GPIO_SPEED_FREQ_HIGH. Is there a solution to this problem?

I tried using a pull-down and pull-up resistors, I also tried another microcontroller. It doesn’t work. I need normal edges for 9 MHz freq