stm32f411 spi4 low clock speed

[mcufan]

Hello!

I have problem with spi4 clock speed. I want to drive a lcd tft display but spi clock is max 500Khz, baudrate prescaler set to SPI_BAUDRATEPRESCALER_2. Is very weird. Initial setup was made with CubeMX to 48Mbit/s. APB2 clock is set to 96Mhz. I tried with dma, and without hal but the speed remains the same

What is the cause of this very low spi clock output speed?

[waclawek.jan]

Read out and check/post the relevant RCC register's content.

Do you use any bootloader?

JW

[mcufan]

I use stm32f411 disco board, the actual spi clk frequency measured with logic analyzer is exactly 500Khz

[mcufan]

I use stm32f411 disco board. The spi sck pin freq. is 500khz measured with logic analyzer

[S.Ma]

You can even make spi by gpio at such speed to test the display functionality, then tune with spi hw peripherals

[waclawek.jan · Accepted solution]

As you can see, although PLL is switched on in CR, PLLCFGR is at its default value; nonetheless your system clock is set to HSI in CFGR, and both APB dividers are set to 16 (maximum).

In other words, you don't run the SystemClock_Config() function as you've presented us above. Find out, how do you actually set the clocks.

JW

[Tesla DeLorean]

Something nominal in SystemInit() would be my guess

[mcufan]

Yes, you are right! I will try to setup the clock somehow.

Thank you!

[mcufan]

Yess! done:) thank you for all. Clive, i set up in the SystemInit() the RCC_CFGR and RCC_PLLCFGR without calling the SystemClock_Config() and now spi is fast as hell:D

[mcufan]

The only mistake was that when i created the code with CubeMX in the RCC setup the HSE selected value was BYPASS Clock Source and not Chrystal/Ceramic Resonator