Hardware / Low-Level

Mini OS

Système minimal démontrant les bases d’un OS.

#include "xc.h"
#include "stdint.h"
#include "stdbool.h"

// =====================================================
// CONFIG
// Adjust these for your PIC18 device
// Example values for many PIC18 parts with internal osc
// =====================================================
#pragma config FOSC = INTIO67
#pragma config WDTEN = OFF
#pragma config LVP = OFF
#pragma config PBADEN = OFF

#define _XTAL_FREQ 8000000UL

// =====================================================
// GLOBAL TICK FLAGS
// =====================================================
volatile uint32_t g_tick_ms = 0;

volatile uint8_t task_1ms_flag   = 0;
volatile uint8_t task_10ms_flag  = 0;
volatile uint8_t task_100ms_flag = 0;
volatile uint8_t task_500ms_flag = 0;

// =====================================================
// GPIO INIT
// Example: LED on RC0
// =====================================================
static void gpio_init(void)
{
    ADCON1 = 0x0F;      // All digital on many PIC18s
    TRISCbits.TRISC0 = 0;
    LATCbits.LATC0 = 0;
}

// =====================================================
// TIMER0 INIT
// Generates ~1 ms tick
//
// Fosc = 8 MHz
// Instruction clock = Fosc/4 = 2 MHz
// Tick period = 0.5 us
//
// Prescaler 1:32 -> timer tick = 16 us
// Need ~1000 us => 62.5 counts
// Preload = 65536 - 63 = 65473 = 0xFFC1
// =====================================================
static void timer0_init(void)
{
    T0CON = 0x00;

    T0CONbits.T08BIT = 0;  // 16-bit timer
    T0CONbits.T0CS = 0;    // Internal clock
    T0CONbits.PSA = 0;     // Prescaler assigned
    T0CONbits.T0PS = 0b100; // 1:32 prescaler

    TMR0H = 0xFF;
    TMR0L = 0xC1;

    INTCONbits.TMR0IF = 0;
    INTCONbits.TMR0IE = 1;
    INTCONbits.GIE = 1;
    INTCONbits.PEIE = 1;

    T0CONbits.TMR0ON = 1;
}

// =====================================================
// TASKS
// =====================================================
static void task_1ms(void)
{
    // Fast task
    // Example: sample inputs, small state machine, etc.
}

static void task_10ms(void)
{
    // Medium-speed task
}

static void task_100ms(void)
{
    // Slow task
}

static void task_500ms(void)
{
    // Blink LED every 500 ms
    LATCbits.LATC0 ^= 1;
}

// =====================================================
// TIMER ISR
// Keep it short: reload timer, update counters, set flags
// =====================================================
void __interrupt() isr(void)
{
    if (INTCONbits.TMR0IF)
    {
        // Reload for ~1 ms
        TMR0H = 0xFF;
        TMR0L = 0xC1;

        INTCONbits.TMR0IF = 0;

        g_tick_ms++;

        task_1ms_flag = 1;

        if ((g_tick_ms % 10U) == 0U)
            task_10ms_flag = 1;

        if ((g_tick_ms % 100U) == 0U)
            task_100ms_flag = 1;

        if ((g_tick_ms % 500U) == 0U)
            task_500ms_flag = 1;
    }
}

// =====================================================
// MAIN
// =====================================================
void main(void)
{
    OSCCON = 0b01110010; // 8 MHz internal osc on many PIC18s

    gpio_init();
    timer0_init();

    while (1)
    {
        if (task_1ms_flag)
        {
            task_1ms_flag = 0;
            task_1ms();
        }

        if (task_10ms_flag)
        {
            task_10ms_flag = 0;
            task_10ms();
        }

        if (task_100ms_flag)
        {
            task_100ms_flag = 0;
            task_100ms();
        }

        if (task_500ms_flag)
        {
            task_500ms_flag = 0;
            task_500ms();
        }

        // Optional: idle / low-power code here
    }
}