slow hspi clock speed on STM32U5G9

[rdl_42]

I am using the hspi1 peripheral in HyperBus mode on an STM32U5G9 processor.

I used STM32CubeMX to configure the hspi clock to 160 MHz, generated from the SYSCLK.  The hspi is configured with 0 Clock Prescaler with the intention of having an external 160 MHz hspi clock.

I went to confirm my clock with a scope, and am only seeing ~140 MHz.  I changed the hspi "Free Running Clock" setting to "Enable" in CubeMX, just for better measurement, and the measured hspi clock speed dropped to ~95 MHz.

Has anyone seen anything like this, or have any suggestions?

Thanks,

-Rob

[Tesla DeLorean]

That's probably unrealistic. You should check on the ratings for the IO cell. Most STM it's below 100 MHz for GPIO, except for specialized pins for DSI

Wire level you might only have a circuit capable of 50-60 MHz, without a lot of ringing or reflections. You'd look at series resistors and lowering the slew rate (OSPEEDR)

In the DDR modes, the clock tends to be lower, and the data comes out on both edges. ie 50 MHz clock, 100 mbps on the data side.

https://www.st.com/resource/en/datasheet/stm32u5g9zj.pdf#page=239

Check also for higher speeds that you have IO Compensation system enabled