Hi I am a newbie to FreeRTOS and is learning about it, I am using FreeRTOS on a PIC32MX460F512L it is supposed to drive a hobby RC servo motor. Earlier I have developed the servo code in  a separate control loop program and confirmed that it worked. However when I put them into the RTOS it don’t work, the servo simply don’t move. Also mounted on the servo is an IR sensor connected to an external interrupt pin. To test code, I connected the PIC32 to the PC via USB the program is working, the MPLAB output display window showed the task switching, the various ISRs being entered and the IR sensor (ext interrupt) is working (I coded it to blink an LED when interrupted). So I am not sure what went wrong I was hoping those with more experience can point out my mistakes, code below:

/* MPLAB includes */
#include <p32xxxx.h>
#include <plib.h>
/* FreeRTOS.org includes */
#include "FreeRTOS.h"
#include "task.h"
#include "semphr.h"
/* Demo includes */
#include "basic_io.h"
///////////////////////////////////
// **** PIC32 Configuration **** //
///////////////////////////////////
#pragma config FPLLODIV = DIV_1, FPLLMUL = MUL_20, FPLLIDIV = DIV_2, CP = OFF
#pragma config FWDTEN = OFF, FPBDIV = DIV_2, POSCMOD = XT, FNOSC = PRIPLL
///////////////////////////////////
// **** Tasks to be created **** //
///////////////////////////////////
static void vServoSensorTask( void *pvParameters );
static void vMovementTask( void *pvParameters );
////////////////////////////////
// **** Servo Definitions ****//
////////////////////////////////
#define   Servo_Min_Pos        30
#define   Servo_Mid_Pos        60
#define   Servo_Max_Pos        90
#define   Servo_Init_Pos          Servo_Min_Pos
#define   Servo_Dir_Clkwise      1
#define   Servo_Dir_CClkwise   0
#define   LD1_ON                    LATBSET = (1<<10)
#define   LD2_ON                          LATBSET = (1<<11)
#define   LD1_OFF                        LATBCLR = (1<<10)
#define   LD2_OFF                        LATBCLR = (1<<11)
////////////////////////////////
// **** Global Variables **** //
////////////////////////////////
unsigned int Servo_Direction = Servo_Dir_Clkwise;              //Track servo direction.
  signed int servo_step_index = 0                                               //Track the servo sweep position.
const unsigned int Servo_stepping[13] = {30, 35, 40, 45,    //This array controls the degree
                        50, 55, 60, 65, //of the sweep of the servo.    
                        70, 75, 80, 85, 90};
const char str1[] = "IR Sensor triggered!n";
const char str2[] = "Timer2 is running...n";
const char str3[] = "OC1 has triggered!n";
int flag1 = 0;
int flag2 = 0;
int flag3 = 0;
//////////////////////////////////////////
// **** Interrupt Service Routines **** //
//////////////////////////////////////////
void __ISR(_TIMER_2_VECTOR, ipl2) Timer2Handler(void){
     mT2ClearIntFlag();  //Clear timer2 interrupt flag.
     switch(Servo_Direction)
     {
          case Servo_Dir_Clkwise:
    servo_step_index += 1;
    OC1R = Servo_stepping[servo_step_index];
    break;
         case Servo_Dir_CClkwise:
    servo_step_index -= 1;
    OC1R = Servo_stepping[servo_step_index];
    break;
         }  
    flag2 = 1;
    LATGSET = (1<<12);  //Starts servo pulse
}
void __ISR(_OUTPUT_COMPARE_1_VECTOR, ipl7) OC1Handler(void){

      LATGCLR = (1<<12);    //Ends servo pulse.
      switch(servo_step_index)
      {
    case 0:
    Servo_Direction = Servo_Dir_Clkwise;
    break;
    case 13:
    Servo_Direction = Servo_Dir_CClkwise;
    break;  
       }
    flag3 = 1;
    mOC1ClearIntFlag(); //Clear OC1 interrupt flag. 
}
void __ISR(_EXTERNAL_1_VECTOR, ipl7) ExtInt1Handler(void)
{
         mINT1ClearIntFlag(); //CLear Ext interrupt 1 flag.

        mPORTBToggleBits(BIT_10); //Toggle LD1
         flag1 = 1;       
}
////////////////////////////////////////////////////////////////
// **** Basic hardware and debug interface configuration **** //
////////////////////////////////////////////////////////////////
void vSetupEnvironment( void );
int main(void)
{
    /* Configure both the hardware and the debug interface. */
    vSetupEnvironment();
    xTaskCreate( vServoSensorTask, "ServoSensor", 240, NULL, 1, NULL );
    xTaskCreate( vMovementTask, "Movement", 240, NULL, 1, NULL );
    /* Start the scheduler so the created tasks start executing. */
    vTaskStartScheduler();
         
    for( ;; );
    
    return 0;
}
static void vServoSensorTask( void *pvParameters )
{    
    for( ;; )
    {
        /* To get here the event must have occurred. Process the event (in this
           case we just print out a message). */
        vPrintString( "ServoSensor Task running...n" );
        if(flag1 == 1)
        {
           flag1 = 0;
           vPrintString(str1);
        }
        if(flag2 == 1)
        {
           flag2 = 0;
           vPrintString(str2);
        }
    }
}
static void vMovementTask( void *pvParameters )
{
    /* As per most tasks, this task is implemented within an infinite loop. */
    for( ;; )
    {
      vPrintString("Movement Task running...n");
      if(flag2 == 1)
      {
         vPrintString(str3);
      }
    }
}
void vSetupEnvironment( void )
{
    /* Setup the main clock for maximum performance, and the peripheral clock
       to equal the main clock divided by 8. */
    SYSTEMConfigPerformance( configCPU_CLOCK_HZ );
    mOSCSetPBDIV( OSC_PB_DIV_8 );
    
   
    PORTDCLR = ((1<<1)|(1<<2)|(1<<6)|(1<<7));   //Output pins
    TRISDCLR = ((1<<1)|(1<<2)|(1<<6)|(1<<7));
    TRISCSET = ((1<<1)|(1<<2));                 //Input pins
    TRISDSET = ((1<<9)|(1<<10));
    TRISB = 0x0;    
    //TRISG = 0x0;  //Set TRISG as output.
    PORTB = 0x0;    
    PORTG = 0x0;  //Set PORTG as off.

    mPORTBSetPinsDigitalOut(BIT_10);     
    mPORTGSetPinsDigitalOut(BIT_12);
    mPORTESetPinsDigitalIn(BIT_8);  //Set RE8 as digital input for INT1  
    
    ////////////////////////////////////////////////////////////////////////
   //                             //
   //    Ext Interrupt 1              //
   //                     //
   //////////////////////////////////////////////////////////////////////// 
ConfigINT1(          EXT_INT_PRI_7| //Set priority 7.
    EXT_INT_SUB_PRI_2| //Set subpriority 2.           
                          RISING_EDGE_INT| //Trigger on rising edge.          
                           EXT_INT_ENABLE); //Enable interrupt.

mINT1ClearIntFlag(); //Clear Ext interrupt 1 flag.  

////////////////////////////////////////////////////////////////////////
//               //
//   Timer 2 Setup       //
//                   //
////////////////////////////////////////////////////////////////////////
//Configure Timer 2 using internal clock, 1:256 prescale
  OpenTimer2(T2_ON | T2_SOURCE_INT | T2_PS_1_256, 1562); //PR1 = 1562, overflows
                                 //every 40ms.
    //Set up the timer interrupt with a priority of 2
    ConfigIntTimer2(T2_INT_ON | T2_INT_PRIOR_2);

////////////////////////////////////////////////////////////////////////
//                //
//   Output Compare module 1 Setup     //
//                    //
////////////////////////////////////////////////////////////////////////
OpenOC1(          OC_ON|      //Turns on OC1.
     OC_TIMER_MODE16|     //Use 16-bit timer.
          OC_TIMER2_SRC|      //Use Timer 2.
              OC_HIGH_LOW|                      //OC2 toggles output.
    OC_TOGGLE_PULSE,      //Forces OC1 pin high.
                             0,   //OC1RS value.
               Servo_Mid_Pos);    //OC1R  value.
ConfigIntOC1( OC_INT_PRIOR_7|    //OC1 interrupt priority is 7.
     OC_INT_SUB_PRI_2|    //OC1 sub priority is 2.
                                     OC_INT_ON);     //OC1 interrupts enabled.

    /* Enable global interrupt handling. */
    INTEnableSystemMultiVectoredInt();
    DBINIT();
}

I also have an asm wrapper file, not sure if I needed it so I just included it

/**********************************************************************
  Interrupts used : 
  - Timer 1, 2 & 3
  - Output Compare Module 1
  - External Interrupt 1
 **********************************************************************/
#include <p32xxxx.h>
#include <sys/asm.h>
#include "ISR_Support.h"
   .set nomips16
   .set noreorder
   
   /* Below are needed in this wrapper file */
   .extern pxCurrentTCB
   .extern vTaskSwitchContext
   .extern vPortIncrementTick
   .extern T1InterruptHandler
   .extern Timer2Handler
   .extern OC1Handler
   .extern ExtInt1Handler
   .extern xISRStackTop
   /* Below are labels */
   .global T1InterruptHandlerWrapper
   .global T2InterruptHandlerWrapper
   .global OC1nterruptHandlerWrapper
   .global ExtInterrupt1HandlerWrapper
   /*.global T3InterruptHandlerWrapper*/
/**************************************/
/* Handler Implementation for Timer 1 */
/**************************************/
/*
   .section     .FreeRTOS, "ax", @progbits
   .set noreorder
   .set noat
   .ent T1InterruptHandlerWrapper
T1InterruptHandlerWrapper:
   portSAVE_CONTEXT
   jal  Robot_Turning
   nop
   portRESTORE_CONTEXT
   .end  T1InterruptHandlerWrapper
*/
/**************************************/
/* Handler Implementation for Timer 2 */
/**************************************/
   .section     .FreeRTOS, "ax", @progbits
   .set noreorder
   .set noat
   .ent T2InterruptHandlerWrapper
T2InterruptHandlerWrapper:
   portSAVE_CONTEXT
   jal  Timer2Handler
   nop
   portRESTORE_CONTEXT
   .end  T2InterruptHandlerWrapper
/**************************************/
/* Handler Implementation for Timer 3 */
/**************************************/
/*
   .section     .FreeRTOS, "ax", @progbits
   .set noreorder
   .set noat
   .ent T3InterruptHandlerWrapper
T3InterruptHandlerWrapper:
   portSAVE_CONTEXT
   jal  T3InterruptHandler
   nop
   portRESTORE_CONTEXT
   .end  T3InterruptHandlerWrapper
*/
   
   
/**************************************/
/* Handler Implementation for OC 1    */
/**************************************/
   .section     .FreeRTOS, "ax", @progbits
   .set noreorder
   .set noat
   .ent OC1InterruptHandlerWrapper
OC1InterruptHandlerWrapper:
   portSAVE_CONTEXT
   jal  OC1Handler
   nop
   portRESTORE_CONTEXT
   .end  OC1InterruptHandlerWrapper
   
   
/****************************************/
/* Handler Implementation for Ext Int 1 */
/****************************************/
   .section     .FreeRTOS, "ax", @progbits
   .set noreorder
   .set noat
   .ent ExtInterrupt1HandlerWrapper
ExtInterrupt1HandlerWrapper:
   portSAVE_CONTEXT
   jal  ExtInt1Handler
   nop
   portRESTORE_CONTEXT
   .end  ExtInterrupt1HandlerWrapper

By the way only timer2, OC1 and ext interrupt 1 is used at the moment. Thanks in advance. Regards,
Kim

Hi there, Here are a few things that you might want to look into: 1) Ensure that no interrupts are firing before the scheduler starts.
2) Ensure that any interrupts that are using FreeRTOS APIs are below that of FreeRTOS’ configMAX_SYSCALL_INTERRUPT_PRIORITY.
3) Ensure that you have enough stack space for each of your created Task. Just curious, are your Tick Interrupts coming in? Cheers,
Ivan

Hi Ivan Tried some of the things you said,

1) Ensure that no interrupts are firing before the scheduler starts.

In the setup I set the peripherals and interrupts off and set them on in one of the tasks with no luck, the program still runs but the servo don’t move.

2) Ensure that any interrupts that are using FreeRTOS APIs are below that of FreeRTOS’ configMAX_SYSCALL_INTERRUPT_PRIORITY.

In my program, configMAX_SYSCALL_INTERRUPT_PRIORITY is set at 4, I set timer2 and OC1 priority to 2 and INT1
priority to 3, again the program runs but servo don’t move.

3) Ensure that you have enough stack space for each of your created Task.

Each task is assigned a stack of 240, I think it is enough as this amount is taken from sample programs by Richard Barry, himself stated 240 is more than enough for ordinary use.

Just curious, are your Tick Interrupts coming in?

I am not too sure how to check this…but I think it should be as the program does run. Regards, Kim