Thank you Jeff,
I did a lot of experiments since I got your reply and I have some unclear behavior that I hope you can explain.
Even if I does not set anything in the pre sleep function and there is no other wakeup mechanism in my program (Like setting RTC wakeup after x seconds for example) the system somehow wake up after the maximum time of a 24bit clock at 4MHz (Which is my core clock speed for the testing I’m doing) that is around 4 seconds (4194 is the FreeRTOS calculation of this max time) and then goes to sleep again and this thing continue forever if no task is ready.
How come? What’s wake up the system at this rate?
I thought that if I HAL_SuspendTick then things are stand still.