CAF Click Detector events too slow (latency)

RE: CAF Click Detector events too slow (latency)

neo_here — Sat, 31 Aug 2024 19:18:54 GMT

Looks like the delay is mostly because of the logger running at a much lower priority than other threads. Even with RTT you'll need to enable immediate logging to see the actual latency times.

So testing the latency with logging is not a great idea. Although as I looked through the button debounce/ghosting logic it seems very conservative.

Anyways, hoping this helps someone.

RE: CAF Click Detector events too slow (latency)

neo_here — Wed, 28 Aug 2024 20:51:20 GMT

The debounce logic seems to be taking too much time. It would be great if someone could help me debug this.

RE: CAF Click Detector events too slow (latency)

neo_here — Wed, 28 Aug 2024 20:34:16 GMT

Specifically this condition

if ((is_pressed != was_pressed)
&& (is_pressed == is_raw_pressed)
&& (evt_limit < CONFIG_CAF_BUTTONS_EVENT_LIMIT))
{
}

(is_pressed != was_pressed) this condition takes about 20-100 scans to evaluate to true. With the scan interval set to 2ms, is this amount of settling time normal ? I'm guessing this delay depends on what kind of debouncing we have on the hardware side as well ?

RE: CAF Click Detector events too slow (latency)

neo_here — Wed, 28 Aug 2024 20:11:35 GMT

Looks like most of the delay is caused due to the the code written to prevent debouncing and ghosting.

At stock configs for

#define SCAN_INTERVAL CONFIG_CAF_BUTTONS_SCAN_INTERVAL
#define DEBOUNCE_INTERVAL CONFIG_CAF_BUTTONS_DEBOUNCE_INTERVAL

I see the scan function being called anywhere from 20-100 times. Which adds varying amounts of delay before the events are sent out. Every call of scan_fn adds about 3-4ms of delay.

static void scan_fn(
struct k_work* work)

RE: CAF Click Detector events too slow (latency)

neo_here — Wed, 28 Aug 2024 19:35:05 GMT

Hi Swathy,

I was able to mess around a bit more, found that the button events themselves have a latency of about 500ms which adds to the click detector latency.

I was looking through buttons.c and wondering if the reason they're delayed is because of the usage of delayable work units.

static struct k_work_delayable matrix_scan;
static struct k_work_delayable button_pressed;

I'm wondering if the delay is caused due to the kernel context switch from sysworkq at -1 priority to a delayable work unit.

RE: CAF Click Detector events too slow (latency)

SwRa — Tue, 13 Aug 2024 12:41:46 GMT

Hi Chinmay,

Sorry for the delay. It was Summer holidays here in Norway and hence we had most of us away on vacation.

The timeout was set so it would be possible to distinguish between single, double and long presses. The internal check is done every 100ms. Short click is by default 500ms so I expect you can get a delay of 500ms + 100ms before it is registered.

One could set the short click delay in the configuration to be something shorter (150ms-200ms) (see sdk-nrf/subsys/caf/modules/Kconfig.click_detector at main · nrfconnect/sdk-nrf (github.com)).

At the moment you will have to change the code here: sdk-nrf/subsys/caf/modules/click_detector.c at main · nrfconnect/sdk-nrf (github.com)

Regards,

Swathy

RE: CAF Click Detector events too slow (latency)

neo_here — Thu, 11 Jul 2024 23:40:54 GMT

Thank you! that will be great

RE: CAF Click Detector events too slow (latency)

SwRa — Thu, 11 Jul 2024 11:40:06 GMT

HI Chinmay,

I have reported this internally and will get back to you with updates.

Regards,

Swathy

RE: CAF Click Detector events too slow (latency)

neo_here — Tue, 09 Jul 2024 02:12:30 GMT

Hey Swathy, I am using the nRFConnect SDK 2.6.1

RE: CAF Click Detector events too slow (latency)

SwRa — Mon, 08 Jul 2024 13:36:01 GMT

Hi Chinmay,

Could you let me know which version of the nRF Connect DK you are using.?

Regards,

Swathy