Thread called only once when thread is created

Questions » Thread called only once when thread is created

8 years, 4 months ago.

Hi , I tried a thread program to glow an LED in the Disco-L476VG board.But the thread i s called only once when created.

I have toggled another LED in main thread which keeps going but new thread is called only once.

My prog

#include "mbed.h"
#include "rtos.h"

Thread thread;

 DigitalOut led_red(LED2);

  DigitalOut led_green(LED1);

void led2_thread(DigitalOut *led) {

    while (true) {

        *led = !*led;

        Thread::wait(1);
    }
}
 
int main() {
    
    thread.start(led2_thread,&led_red);
    
    while (true) {

        led_green = !led_green;

        Thread::wait(500);
    }
}

What would be the prob,I am using mbed-os version 5.3.3 .

Is thread is not stable with STM32 ?

Thanks, E.k

4 Answers

8 years, 4 months ago.

You cannot read the value of the LED through *led, as it returns the object (and does not use the operator overloading which is normally used) and thus always evaluates to the same value. E.g. *led on my NUCLEO-F411RE returns 32 all the time, thus the same value is written to the LED.

Instead, do this:

*led = !led->read();

Zoltan Hudak

8 years, 4 months ago.

Hello Karthick,

Instead of calling Thread::wait(float) try to call wait(float) (or wait_ms(int)) as below.
NOTE: I assume that the 500s delay in main's while loop was a typo not an intention.

#include "mbed.h"
#include "rtos.h"

Thread      thread;
DigitalOut  led_green(LED1);
DigitalOut  led_red(LED2);

void led2_thread(DigitalOut* led) {
    while (true) {
        *led = !*led;
        wait(1.0);
    }
}

int main(void) {
    thread.start(callback(led2_thread, &led_red));

    while (true) {
        led_green = !led_green;
        wait(0.5);
    }
}

Sorry, it seems that the typo wasn't in the main's while loop but in the led2_thread function. Nevertheless, both solutions (with wait(float) above as well as with Thread::wait(int) below) should work fine.

#include "mbed.h"
#include "rtos.h"

Thread      thread;
DigitalOut  led_green(LED1);
DigitalOut  led_red(LED2);

void led2_thread(DigitalOut* led) {
    while (true) {
        *led = !*led;
        Thread::wait(1000);
    }
}

int main(void) {
    thread.start(callback(led2_thread, &led_red));

    while (true) {
        led_green = !led_green;
        Thread::wait(500);
    }
}

posted by Zoltan Hudak 30 Jul 2017

David Smart

8 years, 4 months ago.

I believe that Thread::wait(500) is 500 milliseconds. The pre-OS wait(500) is both a blocking wait, and is measured in seconds. (It takes a float, so wait(0.5) would be 500 msec.

Johannes Stratmann

8 years, 4 months ago.

*led = !*led;

works also fine.

        Thread::wait(500);

waits for 500 ms, that is ok. But in led2_thread, you wait only for 1 ms. So your eyes must be damned fast to see the LED blinking :-)

Karthick E

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