SWI Library

The TI-RTOS Energia MT is built upon includes four major types of threads:

• HWI threads or HWIs, are threads triggered by hardware interrupts and have the highest priority.
• SWI threads or SWIs, are threads triggered by software interrupts and come second after the HWIs.
• Task threads, or tasks, each one with its own stack, come third after the HWIs and the SWIs.
• Idle thread has the lowest priority. On Energia MT, it turns the MCU in low power mode.

SWIs and tasks can have up to 32 levels of priority. For more information, please refer to the SYS/BIOS (TI-RTOS Kernel) v6.41 User's Guide.

Unfortunately, the underlying SWI libraries are no longer included in the Energia MT distribution.

The rtosGlobals.h header file contains all the elements shared across the different tasks and includes the mains setup function rtosSetup().

// *** Header rtosGlobals.h

#ifndef rtosGlobals_h

#define rtosGlobals_h

// Core library

#include "Energia.h"

// Include application, user and local libraries

#include "Semaphore.h"

#include "SWI.h"

#include "Event.h"

// Prototypes

// Define variables and constants

Semaphore mySemaphore;

SWI mySWI;

uint32_t chrono;

Event myEvent;

The function associated with the mySWI event posts the myEvent event.

The function attached to the falling PUSH1 event posts the mySWI event.

// SWI function

void functionSWI()

{

    chrono = millis();

    myEvent.send();

}

// PUSH1 function

void functionPUSH1()

{

    mySWI.post();

}

The main setup function, rtosSetup(), 

• defines the semaphore with 1 resource for the Serial port, 
  
• associates the function functionSWI to the mySWI event, 
• initialises the myEvent event, and 
  
• attaches the function functionPUSH1 for the hardware event falling PUSH1.
  

Function functionPUSH1 has the highest priority, followed by function  functionSWI and then the 4 tasks similar to the example for the semaphore library.

// Add optional rtosSetup function

void rtosSetup()

{

    Serial.begin(115200);

    mySemaphore.begin(1);

    mySWI.begin(functionSWI);

    myEvent.begin();

    

    mySemaphore.waitFor();

    Serial.println("rtosSetup");

    mySemaphore.post();

    

    pinMode(PUSH1, INPUT_PULLUP);

    attachInterrupt(PUSH1, functionPUSH1, FALLING);

}

#endif

The specific sketch greenLED.ino initialises the GREEN_LED output and waits for the event myEvent to blink the green LED.

The other sketches or tasks are similar to the example for the semaphore library.

// *** Sketck greenLED.ino

// Setup

void greenLED_setup()

{

    pinMode(GREEN_LED, OUTPUT);

}

// Loop

void greenLED_loop()

{

    myEvent.waitFor();

    

    blink(GREEN_LED, 3, 333);

    

    digitalWrite(RED_LED, LOW);

    digitalWrite(BLUE_LED, LOW);

    

    mySemaphore.waitFor();

    

    Serial.print(millis(), DEC);

    Serial.println("\t4\t*");

    

    mySemaphore.post();

}

SWI with Trigger Library Variant

The SWI offers an interesting option called trigger.

The SWI mySWItrigger is defined with a trigger, here 3.

The function functionSWItrigger associated with mySWItrigger event is fired 

• after mySWItrigger.dec(), only when the count reaches 0, but 
  
• always after mySWItrigger.inc() or mySWItrigger.post().
  

So the button PUSH1 needs be pressed and released three times before the function functionSWItrigger is fired and myEvent sent.

The example includes additional LEDs, 

• blue when button PUSH1 is pressed and released and mySWItrigger is counting, and 
  
• red when the count reaches the trigger and runs functionSWItrigger.
  

Once functionSWItrigger, has run, the count resumes the initial value of the trigger, here 3.

// *** Header rtosGlobals.h

// Include application, user and local libraries

#include "SWItrigger.h"

// Define variables and constants

SWItrigger mySWItrigger;

// SWItrigger function

void functionSWItrigger()

{

    chrono = millis();

    digitalWrite(BLUE_LED, LOW);

    digitalWrite(RED_LED, HIGH);

    myEvent.send();

}

// PUSH1 function

void functionPUSH1()

{

    digitalWrite(RED_LED, LOW);

    digitalWrite(BLUE_LED, HIGH);

    mySWItrigger.dec();

}

// Add optional rtosSetup function

void rtosSetup()

{

    pinMode(RED_LED, OUTPUT);

    pinMode(BLUE_LED, OUTPUT);

    

    Serial.begin(115200);

    mySemaphore.begin(1);

    mySWItrigger.begin(3, functionSWItrigger);

    myEvent.begin();

    

    mySemaphore.waitFor();

    Serial.println("rtosSetup");

    mySemaphore.post();

    

    // Solution 2: Energia interrupt

    pinMode(PUSH1, INPUT_PULLUP);

    attachInterrupt(PUSH1, functionPUSH1, FALLING);

}

#endif