1284_ Implementation analysis of FreeRTOS task priority acquisition

All learning summary ： GreyZhang/g_FreeRTOS: learning notes about FreeRTOS. (github.com)

Let's analyze it today FreeRTOS Implementation of the priority acquisition function in , involves 2 Interface , One is uxTaskPriorityGet(), The other is its interrupt safe version uxTaskPriorityGetFromISR().

The implementation of this interface is still very simple , In this implementation, the interrupt is turned off directly , Then get the priority of the task . Why do I need to turn off the interrupt , I think the main reason here is xTask May be NULL, What is required at this time is to obtain the current task priority . If an interrupt occurs , This data may be tampered with .

I have seen several similar macro implementations before , If the incoming handle is empty, it is actually a credential for processing the current task . The task handle itself can be converted to TCB Pointer type , In this way, the priority attribute can be obtained directly .

This is an interrupt safe version , The main processing process is similar to that of the previous interface implementation . The difference is , Since it is ISR in , Then an interrupt has already occurred . This is the time , Firstly, the rationality of interrupt priority is confirmed , But this interface is invalid in my current configuration . next , Not off interrupt , Instead, the interrupt mask is modified to prevent unexpected interrupts . There is no big difference in obtaining the priority attribute value .

This is the implementation of mask modification , When modifying, first make a backup of the original mask , Save the original mask after processing .

The mask saved in the previous step becomes a basis for mask recovery here .

Review this again basepri The function of register , This register sets the minimum priority in the system .ARM The smaller the priority value in, the higher the priority , So this value is set to 80 When , Numerically greater than or equal to 80 The interruption of can not happen .FreeRTOS Able to manage ISR The priority should be the lower segment , Therefore, the setting should exceed the value 80 Of , Or at least equal to 80 Of .

such , The task priority is basically analyzed . The following interface analysis , Continue another day .