Embedded system 16x2 lcd user interface

Question

I'm developing a UI for embedded system application. I have to handle few critical tasks always which are being called in main infinite while() loop.

Program flow enters into sub-menu if key is pressed. Since sub-menu has its own infinite while() loop therefore control can not return back to main loop by on its own. It makes accessing of critical tasks impossible as long as sub-menu is active.

• Is there any way to serve tasks in sub loop which are being called in main loop only?
• One way of accessing is to call them in sub-loop as well. But I don't think its a right approach since UI has 50+ sub-menus and also does sub-loops.

Answer 1

You have not mentioned which MCU you are using but looking at the tag I am assuming you are using PIC MCU. The best solution for your problem is to use FreeRTOS. FreeRTOS is available for PIC18 PIC24 PIC32. You can easily create as many task you want and can also include while(1) inside them.

xTaskCreate( vTask1, "Task 1", 240, NULL, 1, NULL );
xTaskCreate( vTask2, "Task 2", 240, NULL, 1, NULL );
xTaskCreate( vTask3, "Task 3", 240, NULL, 1, NULL );

void vTask1()
{
 for(;;)
 {
    PORTDbits.RD0 = 1;
    vTaskDelay( 1000 / portTICK_RATE_MS );
    PORTDbits.RD0 = 0;
    vTaskDelay( 1000 / portTICK_RATE_MS );

 }
}

same you can do for other task. Now all you need to do is run scheduler

vTaskStartScheduler();

Answer 2

There are many ways of doing this. The one I would use is to create a timer with a periodic interrupt, then call the critical tasks from the timer interrupt handler. The interrupt function will run all the time, no matter what other code is running in the main or sub menu loops.

Another method I have used is to put the call to the critical tasks in the 'wait for key' press function - while waiting for key, do critical taks. This has the advantage of being single threaded and having no concurrent data access issues, but it means you don't exactly know how often the critical tasks will be run - it depends on what the sub menu function has to do to process the key press, which will probably vary in different menus / sub-menus.