4 gpio time machine

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#include <stdio.h>
#include <sys/time.h>
#include <inttypes.h>

uint32_t millis(void) {
    struct timeval tv;
    gettimeofday(&tv,NULL);
    return (((uint32_t)tv.tv_sec)*1000)+(tv.tv_usec/1000);
}

enum states {idle, start, t1_expired,t2_expired,t3_expired,t4_expired};

enum states timer_state = idle;
uint32_t delay = 0;
uint32_t last_time = 0;

void timer_start(void){
    timer_state = start;
}

void timer_run(void){
    if (millis() - last_time < delay){
        return;
    }
    switch(timer_state){
        case idle:
            delay = 0;
            last_time = 0;
            break;
        case start:
            delay = 10; //t1
            last_time = millis();
            printf("start at      %u \n", millis());
            timer_state = t1_expired;
            break;
        case t1_expired:
            last_time += delay; // not use millis() to not accumulate time error
            delay = 20;//t2
            printf("t1 expired at %u \n", millis());
            timer_state = t2_expired;
            break;
        case t2_expired:
            last_time += delay;
            delay = 30;//t3
            printf("t2 expired at %u \n", millis());
            timer_state = t3_expired;
            break;
        case t3_expired:
            last_time += delay;
            delay = 40;//t4
            printf("t3 expired at %u \n", millis());
            timer_state = t4_expired;
            break;
        case t4_expired:
            printf("t4 expired at %u \n", millis());
            timer_state = idle;
            break;
        default:
             printf("warning: default state %u \n", millis());
            timer_state = idle;
            break;
    }
}

int main()
{
    timer_run();
    timer_start();

    while(timer_state != idle){
        timer_run();
    }
    printf("end");

    return 0;
}