STM32F407：Why is the calibration value of Systick set according to the HCLK of 150MHz?

[galaxy]

The maximum HCLK of STM32F407 is 168MHz, while the calibration value of Systick is 150MHz HCLK. What is the reason for setting the calibration value of Systick like this? Why not set the calibration value for Systick based on 168MHz HCLK?

[STOne-32]

Dear @galaxy ,

Welcome in STCommunity and thank you so much for the question !

Here is the explanation  : this calibration value is hardcoded at design side when we synthesize the silicon . At that time in 2010 the target maximum frequency was set to 150MHz stretching the STM32F2 device from 120MHz and adding a Cortex-M4 instead of Cortex-M3. When the silicon came out and already working fine and even better than the initial target Frequency, we upgraded the F407 frequency up to 168MHz without a re-spin of the silicon . But this was many years ago and today market and applications not the same. A natural evolution of this device is the H5 MCUs series reaching up to 250MHz and with Cortex-M33.

Hope it helps you .

STOne-32