Suspending a higher priority Task

Kernel
1

sanhardik wrote on Monday, March 16, 2015:

Dear All,
We are trying a code on Atmel SAM D21 for FreeRTOS. We have defined 2 tasks, one is a UART task that writes a string on the terminal and other one toggles a LED.
The UART task has a higher priority than the LED task.
When the UART task is suspended using vTaskSuspend(uart_task_handle), the LED task which has a lower priority doesnt execute.

Is this expected ?

Thanks

2

rtel wrote on Monday, March 16, 2015:

If the two tasks are independent then, no, that is not expected.

Does the LED task run when the UART task is not suspended?

Regards.

3

embeddedindia wrote on Tuesday, March 17, 2015:

Hi All,
I also found similar issue on SAMD21 Evaluation Board with FreeRtos.

case 1: Uart_Task_priority ==> 1 & LED_Task_Priority ==> 2
Handler is Declared but not assigned to any task.
both the task didn’t execute with suspending the handler

case 2: Uart_Task_priority ==> 2 & LED_Task_Priority ==> 1
Handler is Declared but not assigned to any task.
LED_Task is executed. But, Uart_Task is not executed.
with suspending the handler.

case 3: Uart_Task_priority ==> 2 & LED_Task_Priority ==> 1
Handler is Declared but not assigned to any task.
both the task didn’t execute.
without suspending the handler

case 4: USR_TASK_PRIORITY ===> 3 Uart_Task_priority ==> 2 & LED_Task_Priority ==> 1
handler is assigned to USR_Task
LED_Task & Uart_Task executed.
with suspending the handler.

case 5: USR_TASK_PRIORITY ===> 1 Uart_Task_priority ==> 2 & LED_Task_Priority ==> 3
handler is assigned to USR_Task
Uart_Task is executed. But, LED_Task is not executed.
with suspending the handler.

case 6: USR_TASK_PRIORITY ===> 1 Uart_Task_priority ==> 3 & LED_Task_Priority ==> 2
handler is assigned to USR_Task
LED_Task is executed. But, Uart_Task is not executed.
with suspending the handler.

case 7: USR_TASK_PRIORITY ===> 1 Uart_Task_priority ==> 3 & LED_Task_Priority ==> 2
handler is assigned to USR_Task
LED_Task is executed. But, Uart_Task is not executed.
without suspending the handler.

case 8: USR_TASK_PRIORITY ===> 1 Uart_Task_priority ==> 2 & LED_Task_Priority ==> 3
handler is assigned to USR_Task
Uart_Task is executed. But, LED_Task is not executed.
without suspending the handler.

please helpme out in fixing these issue.

Thank you

4

edwards3 wrote on Tuesday, March 17, 2015:

What do you mean “Handler is Declared but not assigned to any task” and “handler is assigned to USR_Task”, etc? What handler? Could you have a buggy UART driver? Did you try with a simple polling driver in place of whatever you are using now?

5

embeddedindia wrote on Thursday, March 19, 2015:

static xTaskHandle terminal_task_handle; // Declaration of task handler

xTaskCreate(task_USR,(const char *) “USR”,configMINIMAL_STACK_SIZE,NULL,USR_TASK_PRIORITY,terminal_task_handle);

xTaskCreate(task_uart,(const char *) “Uart”,configMINIMAL_STACK_SIZE,NULL,UART_TASK_PRIORITY,NULL);

xTaskCreate(led_task,(const char *) “LED”,configMINIMAL_STACK_SIZE,NULL,LED_TASK_PRIORITY,NULL);

Initially, task_uart & led_task was created to which the handler was not assigned. To further understand we created one more task i.e. task_USR to which we assigned handler. so that we can suspend or resume the task. But, presently we are only suspending the task_USR not resuming it back ever.