Hardware: TI tiva-c TM4C123GXL LaunchPad (MCU: tm4c123gh6pm) FreeRTOS Version: 10.2.0 IDE: keil mdk 5.26.2 I have totally 6 tasks: task1: blinky LED and fetch the state of task2 using eTaskGetState function task2: wait for a Semaphore/Notify (with Highest priority) task3-6: only do vTaskDelay and nothing else In the interrupt handler function of URAT, a Semaphore/Notify is given. When running this project, at first, everything is OK. After a while, the state of task2 is turned into eReady, and is keeping on this state. At the same time: 1. All the other tasks are running correctly. 2. No overflow happens on taks2’s stack. 3. The UART interrupt handler function correctly gives out Sema/Notify. Why the task with the highest priority keeps in eReady state while all the other tasks are scheduling normally?

I’m afraid without seeing some code I don’t know where to start making suggestions. Can you show the task that it taking the semaphore and the ISR to start with?

Thank you so much for your reply. I have already uploaded my project in my post. However, I have already found the key issue. Definitely, the interrupt priority. After setting the ISR priority below the configMAXSYSCALLINTERRUPT_PRIORITY, everything is correct now. Thank you all the same.