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[FreeRTOS Home] [Live FreeRTOS Forum] [FAQ] [Archive Top] [August 2006 Threads] Scheduler behavior in non-preemptive modePosted by Tzu-Chien Chiu on August 29, 2006 I have a non-preemptive port of FreeRTOS and there there are totally three tasks:
tskIDLE_PRIORITY = 0 Idle, tskIDLE_PRIORITY Task 1, tskIDLE_PRIORITY + 1 Task 2, tskIDLE_PRIORITY + 2
Task 1 and 2 is created using the same function:
portTASK_FUNCTION(task_proc, params) { unsigned id = *(unsigned*) params; while (1) { printf("*%d* ", id); taskYIELD(); } }
But Task 1 *never* gets a chance to run. After reading vTaskSwitchContext(), I found that Task 1 is starved because Task 2 is *always* in the ready list, and uxTopReadyPriority is always 2.
Is this behavior expected?
-- Tzu-Chien Chiu - SMedia Technology Corp. URL: http://www.csie.nctu.edu.tw/~jwchiu/
RE: Scheduler behavior in non-preemptive modePosted by Nobody/Anonymous on August 29, 2006 Yes, this would be expected because task 2 never blocks. It is always the highest priority task that is able to run.
If you replaced taskYIELD() with vTaskDelay( 2 ), then task 2 would block for 2 ticks, allowing task 1 to execute.
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