1.What is System_Tick() interrupt priority in FREE RTOS ?
Search for configKERNEL_INTERRUPT_PRIORITY on this page RTOS for ARM Cortex-M and other pages on the website.
2.What is the range of Tasks priority in Free RTOS ?
3.What is the range of ISR priority in Free RTOS ?
That depends on the MCU as not all Cortex-M devices have the same priority ranges. See the link posted in answer to question 1 and the user manual for your STM32.
4.Can in use librery functions in ISR ( for example memset in ISR) ?
That depends on the library function. Juse when writing a bare metal application (with no OS) callilng memset() should be fine, but calling something like malloc() or printf() would be a very bad idea.
These are the equivalent of taskENTER_CRITICAL() and taskEXIT_CRITICAL() for us in ISRs and are used to avoid race conditions. You can call taskENTER_CRITICAL_FROM_ISR() and taskEXIT_CRITICAL_FROM_ISR() too which makes this more obvious. You will find examples of how the functions are used inside the queue.c file.
Can System Tick preempt ISR’s ?
System tick is an ISR so I think this has already been answered. Normally the system tick is the lowest priority ISR.
memcpy() itself does not need a critical section. The only time you
would need a critical section is if the buffer being memcpy’ed to or
from could be accessed by another task while the memcpy operation was in
progress.
If there are any occasions that you need to use a critical section in an
interrupt then use taskENTER_CRITICAL_FROM_ISR() and
taskEXIT_CRITICAL_FROM_ISR() in place of taskENTER_CRITICAL() and
taskEXIT_CRITICAL(). See http://www.freertos.org/taskENTER_CRITICAL_FROM_ISR_taskEXIT_CRITICAL_FROM_ISR.html
for information on how to use the _FROM_ISR() versions.
Is a local variable of task remains his value after context switch to another task and back or the local variable of a task reinitilized to his original value ?