Foundations > Multitasking

Multitasking

Multitasking is the ability to run multiple tasks or threads concurrently on a microcontroller. In Energia MT or EMT, multitasking is achieved by treating each tab as a separate task and letting TI-RTOS and Energia take care of the rest. Currently, Multitasking is supported on the MSP432, CC3200 LaunchPads, the RedBearLabs CC3200, WiFi Mini and Micro and the CC2650 SensorTag. The boards are identified with EMT in the Tools->Board menu.

 

Setting up Multitasking applications in Energia MT

Each tab in Energia MT will be treated as a new task, assuming the tab has a setup() and loop() function with a matching and unique name.  For example, an application with 2 tasks could be called setupTask1()/loopTask1() and setupTask2()/loopTask2(). Energia MT will look for these keyword pairs and automatically turn them into tasks.  Its also important that each setup/loop pair be in a file with a “.ino” extension.  Setup/loop pairs that are in .c files will not be treated as a new task and therefore will not execute at run time.

Interprocess communication can easily be done by using global variables. Global variables are truly global (so you cannot use the variable name again in any other tab) and globals must be declared in the first tab.

 

Example

A classic example to show multitasking in an embedded application is to blink multiple LEDs at different rates.  While this sounds simple, it can become very complex in a single threaded application. To begin, we need to set up three tabs, each with a setup() and loop() function. We will also define which LED will be used in each tab with a #define statement. For the MSP432, the tri-color LED is aliased to GREEN_LED, BLUE_LED, and RED_LED.

In the setup() function, we will define the LED as an output using pinMode().

In each loop tab, we will toggle the LED with digitalWrite (high or low depending on whether we want to turn the LED on or off) and different delay() values so the LEDs toggle at different rates.

Tab 1

#define LED BLUE_LED
void setup() { 
 // initialize the digital pin as an output.
 pinMode(LED, OUTPUT); 
}
void loop() {
 digitalWrite(LED, HIGH); //turn the LED on by making the voltage HIGH
 delay(100); // wait for a second
 digitalWrite(LED, LOW); //turn the LED off by making the voltage LOW
 delay(100); // wait for a second
}

Tab 2

#define LED GREEN_LED
void setupGreenLed() { 
 // initialize the digital pin as an output.
 pinMode(LED, OUTPUT); 
}
void loopGreenLed() {
 digitalWrite(LED, HIGH); // turn the LED on 
 delay(500);  // wait for half a second
 digitalWrite(LED, LOW); // turn the LED off 
 delay(500); // wait for half a second
}

Tab 3

#define LED RED_LED
void setupRedLed() { 
 // initialize the digital pin as an output.
 pinMode(LED, OUTPUT); 
}
void loopRedLed() { 
digitalWrite(LED, HIGH); // turn the LED on 
 delay(1000); // wait for 1/10 second
 digitalWrite(LED, LOW); // turn the LED off 
 delay(1000); // wait for 1/10 second
}

This example can be found in Energia MT under File -> Examples -> MultiTasking -> MultiBlink

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