Zephyr Timer + I2C

[josh_s]

I'm building a simple application using I2C to read sensor data (BNO055). I confirmed I2C and my sensor are all configured appropriately and working smoothly, but when I added in zephyr timers to my application to read the sensors, the application repeatedly crashes.  I've confirmed that both I2C and the timers work as expected independently, but not when used together.  Please see some sudo-code below:

static void repeating_timer_callback(struct k_timer *timer_id){

        i2c_read_write(...);

        ...

}

K_TIMER_DEFINE(my_timer, repeating_timer_callback, NULL);

void main(){

             ...

             ...

            k_timer_start(&my_timer, K_MSEC(100), K_MSEC(100));

} 

[qwertynoon]

Hi.

I2C can take a lot of time, thats why you shoud use K_WORK_DEFINE for your timer

Try this

static void repeating_timer_callback(struct k_timer *timer_id){

        i2c_read_write(...);

        ...

}

K_WORK_DEFINE(repeating_timer_work, repeating_timer_callback);

void repeating_timer_handler(struct k_timer *dummy)
{
        k_work_submit(&repeating_timer_work);
}

K_TIMER_DEFINE(my_timer, repeating_timer_handler, NULL);

[josh_s]

Thanks, but doesn’t that submit solution not force the sensor to read every 100ms as intended?  In other words, once submitted via k_work_submit, the i2c instructions may await execution for a variable amount of time, and therefore I may not get 100ms intervals on the sensor reads. 

[Simon]

Doing a lot of work inside an ISR is not good practice, and it should be offloaded to somewhere else.

Check out these solutions as well as the one suggested by qwertynoon

Timer + semaphore: https://devzone.nordicsemi.com/f/nordic-q-a/74617/config_assert-cause-code-to-crash/307651#307651. 

• You could also put the snippet below in an own thread instead of having it in main

while(true){
        k_sem_take(&adc_sem, K_FOREVER);
        adc_sample();
    }
}

Timer + work queue: https://github.com/too1/ncs-peripheral-uart-adc/blob/d575cdb9a2e0d7e5f0984a6a228bcb0d3a6f1a7c/src/main.c#L563-L565 

I'm not sure what the accuracy will be when using the approches above, and I guess it depends on your application and how much other work you're doing. I suggest you test it yourself and see if it meets your requirements. Maybe increasing the priority of the thread doing the ADC reading will help.

Best regards,

Simon