Hello! I have a fairly large project regarding freertos and microcontrollers, and we are using the arduino mega 2560 for this project. But regarding the size of the project(its not as big now as it will be in the future), how can i best controll memory and not get the stackoverflow? Have searched the web and cant find any good ideas of how to best manage memory. Hope to get some great advice! 🙂

• Dino

Using FreeRTOS makes very little difference to the stack size – the stack size depends on how the compiler uses it (which will be different at different optimisation levels), the function call nesting depth, and the variables your code places on the stack – just like in any C program. The difference when using FreeRTOS (or any preemptive RTOS) is that you have more than one stack – one per task – so you can try to minimise the number of tasks you create. Some C libraries are real stack hogs too, so choose an optmized library implementation. You can view stack sizes using several functions, including https://www.freertos.org/uxTaskGetStackHighWaterMark.html – that enables you to tune the size as you can see if the current size is too large or too small. Likewise you can tune the heap size using xPortGetMinimumEverFreeHeapSize().

Okey, so by using the uxuxHighWaterMark method i can fine tune the amount of stacksize needed for each task? If i then understand you correctly, rtos will do the memory handling for me? So i dont need any realloc(); or malloc(); from freertos lib?

As you say, you can use uxHighWaterMark to check stack usage and adjust your stack size based on it (be sure to leave a bit of slack). FreeRTOS will aquire the needed memory to create that stack for you (unless you use the ‘Static’ task creation routine, where you provide the needed array, assume to be allocated as static memory) If your tasks need any dynamic memory, they will need to call the allocation functions themselves. This is just like for any normal program, the only difference is that with multiple tasks, you have multiple task stacks, so you have to allocate the desired amount to each of them.

When im trying to use the uxHighwatermark function i get an error from visual studio: Compiling .pioenvsmegaatmega2560srcmain.cpp.o srcmain.cpp:16:63: error: ambiguating new declaration of ‘UBaseTypet uxTaskGetStackHighWaterMark(TaskHandlet)’ UBaseTypet uxTaskGetStackHighWaterMark(TaskHandlet Startpump); ^ In file included from libFreeRTOSsrc/FreeRTOSVariant.h:56:0, from libFreeRTOSsrc/ArduinoFreeRTOS.h:1270, from srcmain.cpp:2: libFreeRTOSsrc/task.h:1440:24: note: old declaration ‘uint16t uxTaskGetStackHighWaterMark(TaskHandlet)’ configSTACKDEPTHTYPE uxTaskGetStackHighWaterMark( TaskHandlet xTask ) PRIVILEGED_FUNCTION; ^ *** [.pioenvsmegaatmega2560srcmain.cpp.o] Error 1 How to fix?

First thought is that you are mixing source files from different versions of FreeRTOS.

I am currently using 10.2.0v of freertos, i have also read more about usage of uxTaskGetStackHighWatermark, and now it prints, but all i get is a questionmark symbol for each time the task is used. A snip of my code: void Startpump(void *pvParameters); xTaskCreate( Startpump, // Function name “Turn on pump”, // What it does 128, // Stack size in words NULL, // Parameter for task, usually NULL 1, // Priority of the task NULL // Task handle, usually NULL );

vTaskStartScheduler();

The funtion itself: 

void Startpump(void *pvParameters)

{

// Initialize on and off button
pinMode(buttonPin1, INPUT);
pinMode(buttonPin2, INPUT);
pinMode(motorPin, OUTPUT);
pinMode(greenLedPin, OUTPUT);
pinMode(redLedPin, OUTPUT);



// Task commands for delay og minnehåndtering(sjekke verdier hver task spytter ut)
// Delay mellom task
const TickType_t xDelay = 100 / portTICK_PERIOD_MS;

uxHighWaterMark = uxTaskGetStackHighWaterMark( NULL );

for (;;)
{
    // Leser status på knappene
    buttonStatus1 = digitalRead(buttonPin1);
    buttonStatus2 = digitalRead(buttonPin2);


    if (buttonStatus1 == HIGH && buttonStatus2 == LOW) // På knappen trykket
    {
        digitalWrite(motorPin, HIGH);
        digitalWrite(greenLedPin, HIGH);
        digitalWrite(redLedPin, LOW);
        LEDstatus = 1;
        uxHighWaterMark = uxTaskGetStackHighWaterMark( NULL );
        Serial.println(uxTaskGetStackHighWaterMark(NULL));
        vTaskDelay(xDelay);
    }
    else if(buttonStatus1 == LOW && buttonStatus2 == HIGH) // Av knappen er trykket
    {
        digitalWrite(motorPin, LOW);
        digitalWrite(greenLedPin, LOW);
        digitalWrite(redLedPin, HIGH);
        LEDstatus = 0;
        Serial.print(F("Watermark stack er: "));
        uxHighWaterMark = uxTaskGetStackHighWaterMark( NULL );
        Serial.println(uxTaskGetStackHighWaterMark(NULL));
        vTaskDelay(xDelay);

    }

}

} Comments are in norwegian 🙂 Am i using it right?

Which bit is not working? Just the printing? If so, can’t help you there as the print function you are using is not something we wrote – but to check the uxTaskGetStackHighWaterMark() function you can simple place a break point in the code to see its return value.

It wont print values as it says it should. Ill try that, otherwise i have to find another way to get the right values 🙂 thanks!