Calling a function inside a task

[R-INYURU]

I created a task which reads GPS data but it has to call some function out of the task but when i am running them they are not returning anything.
What could be the cause of that?

[feilipu]

I don't really know how to properly respond to the question, with so little information.

I suggest that there is nothing about FreeRTOS that would influence your issue. It is likely to be something to do with the way you're calling your function, or the way the data is being declared, before being returned.

To debug the problem, start by trying to flash a LED by calling a function from within the Task. Once that is working, then you're sure your function is being called.

You can then move on from there by returning a counter, or something else.
Use print statements to check where your code is executing.

Good luck.

[R-INYURU]

I tried the code below to test it but it is printing started only the LED on 13 doesn't blink, what could be the cause?

  #include <Arduino_FreeRTOS.h>

  void Blink(void *pvParameters);

  void setup() {
    Serial.begin(115200);

    xTaskCreate(Blink, (const portCHAR *)"blink", 100, NULL, 2, NULL);
  }

  void loop() {
    Serial.println("will loop infinitily");
  }

  void Blink(void *pvParameters) {
    int pin = 13;

    pinMode(pin, OUTPUT);

    while (true) {
      Serial.println("started");

      if (isPinHIGH == true) {
        digitalWrite(pin, LOW);
        delay(1000);
    }
    else {
      digitalWrite(pin, HIGH);
      delay(1000);
    }
  }
}

bool isPinHIGH() {
  if (digitalRead(13) == HIGH) {
    Serial.println("pin is HIGH");
    return true;
  }
  else {
    Serial.println("pin is LOW");
    return false;
  }
}

[feilipu]

I'm 90% certain your issue is caused by not allocating enough Task stack. You've only 15 bytes more than the minimum. Hardly enough to store one local string.

Using the serial.println() functions requires a lot of local memory.

Change the stack size to 500 bytes, and use the stack management tools to check the highwater levels

Do not assume delay() will give you what you need. It is a busy wait, and relies on not being interrupted. See issue #20 for more.

[R-INYURU]

I have removed the delay() replaced it with vTaskDelay() and added vTaskDelay() in the void loop() otherwise is printing this line Serial.println("will loop infinitely"); infinitely, i left the stack memory to 100 and the led is blinking but it is not printing these lines Serial.println("pin is HIGH"); and Serial.println("pin is LOW"); in bool isPinHIGH() function even if i increase the stack memory to 10000. Below there is new code

#include <Arduino_FreeRTOS.h>

  void Blink(void *pvParameters);

  void setup() {
    Serial.begin(115200);

    xTaskCreate(Blink, (const portCHAR *)"blink", 100, NULL, 2, NULL);
  }

  void loop() {
    Serial.println("will loop infinitely");
    vTaskDelay(10000);  //Any number of ticks you enter it will work fine.
  }

  void Blink(void *pvParameters) {
    int pin = 13;

    pinMode(pin, OUTPUT);

    while (true) {
      Serial.println("started");

      if (isPinHIGH == true) {
        digitalWrite(pin, LOW);
        vTaskDelay(500);
    }
    else {
      digitalWrite(pin, HIGH);
      vTaskDelay(500);
    }
  }
}

bool isPinHIGH() {
  if (digitalRead(13) == HIGH) {
    Serial.println("pin is HIGH");
    return true;
  }
  else {
    Serial.println("pin is LOW");
    return false;
  }
}

[feilipu]

Try removing the TaskDelay() from the loop(). I noted in the readme that the loop() shall never be blocked, because it is called from the IdleTask. Blocking loop() will kill everything.

Then go back to the example, and check it works. Change one thing at a time. See what breaks things.

Use the stack high water management tools in FreeRTOS. Start with stack at 500 bytes, and reduce it from there. That, and heap issues, are the cause of most pain.

C++ (Arduino) consumes lots of stack. That is the cost of convenience.

[karawin]

isPinHIGH is a funtion which need ()
try:

#include <Arduino_FreeRTOS.h>
#define pin 13

  void Blink(void *pvParameters);

  void setup() {
    Serial.begin(115200);
    xTaskCreate(Blink, (const portCHAR *)"blink", 100, NULL, 2, NULL);
  }

  void loop() {
//    Serial.println("will loop infinitely");
//    vTaskDelay(10000);  //Any number of ticks you enter it will work fine.
  }

  void Blink(void *pvParameters) {    
    pinMode(pin, OUTPUT);
   Serial.println("started");
    while (true) {     
      if (isPinHIGH() == true) {
        digitalWrite(pin, LOW);
      }
      else {
     	 digitalWrite(pin, HIGH);
      }
     vTaskDelay(500);
  }
}

bool isPinHIGH() {
  if (digitalRead(pin) == HIGH) {
    Serial.println("pin is HIGH");
    return true;
  }
  else {
    Serial.println("pin is LOW");
    return false;
  }
}

[R-INYURU]

@feilipu if i comment out all lines in the void loop() an d I changed the stack to 500 now the led is not blinking any more only it is printing started.

@karawin i am using isPinHIGH() to try to simulate how to call a function inside a Task.

[karawin]

ok but
if (isPinHIGH == true) {
is not correct.
if (isPinHIGH() == true) {
is correct

without () it is the address of the function which is compared, not the return of the function.

[R-INYURU]

Thank you @karawin i didn't noticed that now everything is working well.
But if we come back to the first comment i was trying to read GPS coordinates and I am using tinyGPS++ library this is the code I am using.

#include <Arduino_FreeRTOS.h>
#include <TinyGPS++.h>

TinyGPSPlus gps;

void GPSreader(void *pvParameters);

void setup() {
  Serial.begin(115200);
  Serial2.begin(9600);    //GPS module
  Serial.println("this is setup func");

  xTaskCreate(GPSreader, "GPSreader", 10000, NULL , 2, NULL);
}

void loop() {}

void GPSreader(void *pvParameters) {
  Serial.println("something atleast");
  while (true) {
    String values;
    char latitude[10], longitude[10], Altitude[8], Speed[10], satelites[3];

    printInt(gps.satellites.value(), gps.satellites.isValid(), 2, satelites);
    printFloat(gps.location.lat(), gps.location.isValid(), 9, 6, latitude);
    printFloat(gps.location.lng(), gps.location.isValid(), 9, 6, longitude);
    printFloat(gps.altitude.meters(), gps.altitude.isValid(), 7, 2, Altitude);
    printFloat(gps.speed.kmph(), gps.speed.isValid(), 6, 2, Speed);

    values  = latitude;
    values += ',';
    values += longitude;
    values += ',';
    values += Altitude;
    values += ',';
    values += Speed;
    Serial.print("GPS: ");
    Serial.println(values); //latitude, longitude, altitude, speed, direction
    //    vTaskDelay(100);
    smartDelay(100);
    if (millis() > 2000 && gps.charsProcessed() < 10)
      Serial.println(F("No GPS data received: check wiring"));
  }
}

void smartDelay(unsigned long ms) {
  unsigned long start = millis();
  do {
    while (Serial2.available())
      gps.encode(Serial2.read());
  } while (millis() - start < ms);
}

void printFloat(float val, bool valid, uint8_t len, uint8_t decPnt, char var[]) {
  if (!valid) {
    while (len-- > 1) {
      dtostrf(val, len, decPnt, var);
    }
  }
  else {
    dtostrf(val, len, decPnt, var);
  }
}

void printInt(uint8_t val, bool valid, uint8_t len, char var[]) {
  if (valid) {
    sprintf(var, "%d", val);
  }
  var[len] = 0;
  for (int i = strlen(var); i < len; ++i) {
    var[i] = '0';
  }
  if (len > 0) {
    var[len - 1] = ' ';
  }
}

these code works well without FreeRTOS. But now it is not starting the task, I know i used the millis() function and i was not supposed to use it so i am going to continue to find a way to remove it but anyone with an idea can help.
Thank you for the support.

[karawin]

I think that you may use
xTaskGetTickCount
task.h
volatile TickType_t xTaskGetTickCount( void );
This function cannot be called from an ISR. Use xTaskGetTickCountFromISR() instead.
Returns:
The count of ticks since vTaskStartScheduler was called.

[feilipu]

You're asking for 10,000 bytes of stack, just for the GPSreader Task alone. If you're trying to run this on an Arduino Uno with 2048 bytes of RAM in total, then you've got a problem. Even a Mega has only 8,192 bytes of RAM. The xTaskCreate() will certainly fail, and you'll get the malloc() fail LED blink (mentioned in the README) at 100ms cycle.

Again, start with a Task stack of about 500 bytes. Not more, and use the task highwater tools to work out how much stack remains unused. Then reduce to leaving (say) 20 bytes free for each task.

Keep the loop() function empty, unless you use it to put the MCU to sleep when it is idle.

FreeRTOS has xTaskDelayUntil() function that can delay a precise number of Ticks, usually divided by the Tick Period to get time in ms. Initialise it before use, by calling xTaskGetTickCount().

To set a one shot or multiple shot Timer, then use the FreeRTOS API for Timers. It is enabled in this port.

Oh, and for convenience if you're writing to a serial port, then it is best to protect it using a MutEx Semaphore, otherwise it is possible for one task to interrupt another task writing to the serial port, and you'll garble the messages.

And, if you're going to be using a lot of string text messages, wrap them in the F("a test message") function. This prevents the strings from being copied from Flash to Data Section in RAM to println() buffer to Serial buffer. They are only copied twice (rather than 3 times).

[R-INYURU]

@feilipu i changed the stack to 500 bytes now it is fine but i am using arduino MEGA with 8Kb of RAM i don't understand why the i get malloc() fail LED blinking.
Thank you again.

[feilipu]

Move these lines outside your while(){ } loop

    String values;
    char latitude[10], longitude[10], Altitude[8], Speed[10], satelites[3];

Whilst the compiler will probably optimise, and not keep on reallocating them, it is best not tempt fate.

And, String is in itself problematic to have on the stack. Arduino String functions are very RAM hungry. Try to move the String values; line to be a global (and therefore on the heap).

Finally, calling millis() in a tight loop will likely cause Scheduler interrupts to be missed. This is happening here. As noted in issue #20.

  do {
    while (Serial2.available())
      gps.encode(Serial2.read());
  } while (millis() - start < ms);

[R-INYURU]

I moved those line above out of the while(){} and i made String values; variable global and I am getting Serial.print(F(GPS: )); printed but Serial.println(values); is printing nothing it seems that is not able to call void printFloat(...) and void printInt(...) functions or may be is because i am still using the millis(). About the serial port, for now i have one task thats why i didn't use the semaphore and is for debugging only.

[R-INYURU]

I have continued to try to solve that problem but i noted something, the TinyGPS++ library am using is written in C++ but FreeRTOS is in C and am trying to use String datatype which doesn't work with C programming so i also tried using char* of C programming which was able to return a string but i wasn't able to concatenate two variable with char* datatype. So any idea will be appreciated.

[karawin]

strcat, strcpy, sprintf etc, learn a bit more about the possibilities.

[R-INYURU]

Thanks a lot for everything now everything is working fine.
Below there is source code in case anyone may need them.

#include <Arduino_FreeRTOS.h>
#include <timers.h>
#include <TinyGPS++.h>

TinyGPSPlus gps;

void GPSreader(void *pvParameters);

TimerHandle_t GPStimer;
void GPSid() {}

void setup() {
  Serial.begin(115200);
  Serial2.begin(9600);    //GPS module

  GPStimer = xTimerCreate("GPStimer", 100 / portTICK_PERIOD_MS, pdFALSE, GPSid, smartDelay);

  if (GPStimer == NULL)
    Serial.println(F("timer not created"));
  else
    xTimerStart(GPStimer, 200 / portTICK_PERIOD_MS);

  xTaskCreate(GPSreader, "GPSreader", 350, NULL , 2, NULL);
}

void GPSreader(void *pvParameters) {
  char* comma = ",";
  char values[70];

  while (true) {
    UBaseType_t uxHighWaterMark;
    Serial.println(uxTaskGetStackHighWaterMark(NULL));  //print unused stack memory

    char* Latitude = printFloats(gps.location.lat(), gps.location.isValid(), 9, 6);
    char* Longitude = printFloats(gps.location.lng(), gps.location.isValid(), 9, 6);
    char* Speed = printFloats(gps.speed.kmph(),   gps.speed.isValid(),    6, 2);
    char* SatNumb = printInts(gps.satellites.value(), gps.satellites.isValid(), 5);

    strcpy(values, Latitude);
    strcat(values, comma);
    strcat(values, Longitude);
    strcat(values, comma);
    strcat(values, Speed);

    Serial.println(values);

    vTaskDelay(200 / portTICK_PERIOD_MS);
    xTimerReset(GPStimer, 200 / portTICK_PERIOD_MS);
    if (xTaskGetTickCount() > 2000 && gps.charsProcessed() < 10)
      Serial.println(F("No GPS data received: check wiring"));
  }

}

void smartDelay(unsigned long ms) {
  while (Serial2.available())
    gps.encode(Serial2.read());
}
/********************************* NEW FOR GPS COORDINATES ******************************/
char* printFloats(float val, bool valid, int len, int decPnt) {
  char var[32];
  if (!valid) {
    while (len-- > 1) {
      var[15] = "********";
    }
  }
  else {
    dtostrf(val, len, decPnt, var);
  }
  return var;
}

char* printInts(unsigned long val, bool valid, int len) {
  char var[32];
  if (valid)
    sprintf(var, "%ld", val);
  var[len] = 0;
  for (int i = strlen(var); i < len; i++)
    var[i] = ' ';
  if (len > 0)
    var[len - 1] = ' ';
  return var;
}

void loop() {}