Microchip Forums: RTOS implementation - Inline C

/*
 * File:   main.c
 * Author: abdullah
 *
 * Created on 10 Haziran 2012 Pazar, 14:43
 */
#include <xc.h> // Include the header file needed by the compiler
__CONFIG(FOSC_INTOSCIO & WDTE_OFF & PWRTE_ON & MCLRE_OFF & CP_OFF & IOSCFS_4MHZ & BOREN_ON);

#define numOfTasks 4
unsigned char currentTask; // This TCB pointer will point to the current task's TCB.
unsigned char tasks[4];

void fTask1(void); // Prototype the function for task1.
void fTask2(void); // Prototype the function for task2.

void main(void)
{
    TRISA = 0; // Set all of the PORTA pins as outputs.
    TRISC = 0; // Set all of the PORTC pins as outputs.
    ANSEL = 0; // Set all of the analog input pins as digital i/o.
    PORTA = 0; // Clear PORTA bits.
    PORTC = 0; // Clear PORTC bits.

    currentTask = 0;
    fTask1();
    currentTask++;
    fTask2();

#asm
    _taskswitcher
        movlw   0x02                ; W = 2
        addwf   _currentTask, f     ; Add 2 to currentTask, store it in currentTask.
        movlw   numOfTasks          ; W = numOfTasks
        subwf   _currentTask, w     ; w= f - w
        btfsc   status, 0           ; If currentTask >= numOfTasks
        clrf    _currentTask        ; Clear currentTask

        movlw   _tasks              ; Store the address of tasks, which is the start address of our task "array".
        addwf   _currentTask, w     ; Add current task's index to the start address.
                                    ; For example; task1's index is 2:  [task0_1][task0_2][task1_1][task1_2]....
                                    ;                                       0        1        2        3
        movwf   fsr                 ; We have the index of current task in W. Copy it to FSR
        movf    indf, w             ; Copy the contents of current task's first item to W
        movwf   pclath              ; Copy W to PCLATH. As a result, current task's PCLATH will be in PCLATH register.

        incf    fsr, f              ; Increment index, so that we will point to the next item of current task.
        movf    indf, w             ; Copy the contents of current task's second item to W.
        movwf   pcl                 ; Copy W to PCL. Finally, current task's PCL will be in PCL register.
#endasm
}

void fTask1(void)
{
#asm
        movlw   _tasks               ; Store the address of tasks, which is the start address of our task "array".
        addwf   _currentTask, w      ; Add current task's index to the start address.

        movwf   fsr                 ; We have the index of current task in W. Copy it to FSR
        movf    pclath, w           ; Copy PCLATH register's contents to W register.
        movwf   indf                ; Copy W to current task's first item. We now store PCLATH.

        incf    fsr,f               ; Increment index, so that we will point to the next item of current task.
        movlw   low($+3)            ; Copy PCL+3 to W register. This will let us save the PCL of the start of the task.
        movwf   indf                ; Copy W to task's next item. With that, we will initialize the current task.
        return                      ; We have gathered our initialazation information. Return back to main.
#endasm

    while (1)
    {
        PORTA = 0xAA; // Toggle PORTA.0

#asm
        movlw   _tasks               ; Store the address of tasks, which is the start address of our task "array".
        addwf   _currentTask, w      ; Add current task's index to the start address.

        movwf   fsr                 ; We have the index of current task in W. Copy it to FSR
        movf    pclath, w           ; Copy PCLATH register's contents to W register.
        movwf   indf                ; Copy W to current task's first item. We now store PCLATH of the current state of the task.

        incf    fsr, f               ; Increment index, so that we will point to the next item of current task.
        movlw   low($+3)            ; Copy PCL+3 to W register. This will let us save the PCL of the current state of the task.
        movwf   indf                ; Copy W to task's next item. With that, we will initialize the current task.

        goto    _taskswitcher        ; Yield the CPU to the awaiting task by going to task switcher.
#endasm

        PORTA = 0x55; // Toggle PORTA.0
    }
}

void fTask2(void)
{
#asm
        movlw   _tasks               ; Store the address of tasks, which is the start address of our task "array".
        addwf   _currentTask, w      ; Add current task's index to the start address.

        movwf   fsr                 ; We have the index of current task in W. Copy it to FSR
        movf    pclath, w           ; Copy PCLATH register's contents to W register.
        movwf   indf                ; Copy W to current task's first item. We now store PCLATH.

        incf    fsr,f               ; Increment index, so that we will point to the next item of current task.
        movlw   low($+3)            ; Copy PCL+3 to W register. This will let us save the PCL of the start of the task.
        movwf   indf                ; Copy W to task's next item. With that, we will initialize the current task.
        return                      ; We have gathered our initialazation information. Return back to main.
#endasm

    while (1)
    {
        PORTA = 0xAA; // Toggle PORTA.0

#asm
        movlw   _tasks               ; Store the address of tasks, which is the start address of our task "array".
        addwf   _currentTask, w      ; Add current task's index to the start address.

        movwf   fsr                 ; We have the index of current task in W. Copy it to FSR
        movf    pclath, w           ; Copy PCLATH register's contents to W register.
        movwf   indf                ; Copy W to current task's first item. We now store PCLATH of the current state of the task.

        incf    fsr, f               ; Increment index, so that we will point to the next item of current task.
        movlw   low($+3)            ; Copy PCL+3 to W register. This will let us save the PCL of the current state of the task.
        movwf   indf                ; Copy W to task's next item. With that, we will initialize the current task.

        goto    _taskswitcher        ; Yield the CPU to the awaiting task by going to task switcher.
#endasm

        PORTA = 0x55; // Toggle PORTA.0
    }
}