Zephyr Timer + I2C

RE: Zephyr Timer + I2C

Simon — Mon, 02 May 2022 12:51:44 GMT

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

RE: Zephyr Timer + I2C

josh_s — Mon, 02 May 2022 12:33:13 GMT

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.

RE: Zephyr Timer + I2C

qwertynoon — Mon, 02 May 2022 06:00:14 GMT

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);