nRF52840 CPU Usage Accuracy and Explanation

RE: nRF52840 CPU Usage Accuracy and Explanation

Jared — Fri, 09 Jun 2023 09:20:00 GMT

Hi Alan,

Can you download SES v5.42a and build the example with that IDE and see if it results in the same?

Also, use SDK v17.1.0,

This is what I used when I tested it last time and got 0% with the addition,

regards

Jared

RE: nRF52840 CPU Usage Accuracy and Explanation

fwd159 — Thu, 08 Jun 2023 20:33:56 GMT

Hi Jared,

I deleted everything I had done previously and tried my algorithm with the original pwr_mgmt example code. Below is how I implemented it:

After compiling and flashing to the dev kit, I see the following on my terminal:

The only changes I made to this project were the addition function implementation and the function call in the main while loop. I'm confused now why the CPU Usage is even higher than before? I tried this code with the dev kit on SDK v16.0.0, but it's my understanding that the results should be the same across SDK versions? Is it possible that you are optimizing for time when you're compiling in the target options?

For reference, I ran this pwr_mgmt project without the addition function and I saw 0% CPU usage.

Regards,

Alan

RE: nRF52840 CPU Usage Accuracy and Explanation

Jared — Mon, 05 Jun 2023 10:06:55 GMT

Hi Alan,

I tried adding the ME_addition() to the pwr_mgmt example and call it from the while loop just as you have done, and I'm not able to replicate the same on my development kit. My development kit shows 0% after adding this, have you done any other changes to your project? Are you able to replicate this on SDK v17.1.0?

regards

Jared

RE: nRF52840 CPU Usage Accuracy and Explanation

fwd159 — Fri, 02 Jun 2023 19:52:30 GMT

Baseline CPU usage without line 30 is 0% (or ~0.3% with floating point representation).

RE: nRF52840 CPU Usage Accuracy and Explanation

Jared — Fri, 02 Jun 2023 11:39:11 GMT

Hi,

What do you measure if you don't add the addition? What is the baseline CPU usage without adding line 30,

regards

Jared

RE: nRF52840 CPU Usage Accuracy and Explanation

fwd159 — Tue, 30 May 2023 14:34:24 GMT

I'm calling ME_addition() inside the main() function's while loop (at line 30). I'll include a code snippet below:

int main(void)
{
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

    NRF_LOG_INFO("Power Management example");

    lfclk_config();

		uint32_t err_code = app_timer_init(); // drv_rtc.c:108 "RTC: initialized."
    APP_ERROR_CHECK(err_code);

#if NRF_PWR_MGMT_CONFIG_USE_SCHEDULER
    APP_SCHED_INIT(APP_SCHED_MAX_EVENT_SIZE, APP_SCHED_QUEUE_SIZE);
#endif // NRF_PWR_MGMT_CONFIG_USE_SCHEDULER
	
    bsp_configuration();

		ret_code_t ret_code = nrf_pwr_mgmt_init(); // nrf_pwr_mgmt.c:326 "Init"
    APP_ERROR_CHECK(ret_code);

    while (true)
    {
			
#if NRF_PWR_MGMT_CONFIG_USE_SCHEDULER
        app_sched_execute();
#endif // NRF_PWR_MGMT_CONFIG_USE_SCHEDULER

			
		ME_addition();
			
        if (NRF_LOG_PROCESS() == false)
        {
            nrf_pwr_mgmt_run();
        }
    }
}

Thanks

RE: nRF52840 CPU Usage Accuracy and Explanation

Jared — Tue, 30 May 2023 14:28:42 GMT

Hi,

How are you calling ME_addition(), in a loop?

regards
Jared

RE: nRF52840 CPU Usage Accuracy and Explanation

fwd159 — Tue, 30 May 2023 14:25:30 GMT

Hi Jared,

Thanks for the timely reply. Without applying any changes to pwr_mgmt_cpu_usage_monitor_update() and running the basic addition function I implemented, the CPU usage is logged at 12%. Of course, without running my addition function, the CPU usage is at 0%.

Regards,

Alan

RE: nRF52840 CPU Usage Accuracy and Explanation

Jared — Tue, 30 May 2023 14:21:48 GMT

Hi,

What do you get if you don't apply the changes to pwr_mgmt_cpu_usage_monitor_update()?

regards

Jared