Reduce MCUBoot startup time

[Yeccc]

We found that it took a long time for the nrfconnect sdk to power on the device to enter the application.
Is there any way to reduce the startup time?

We have closed the log, and the startup time has reached 1.3s.
It is too long for the bulb device, so we need to solve this issue.

[Vidar Berg]

Hi,

Please try to select the RNG — Random number generator as the entropy source instead of using the CRYPTOCELL — ARM TrustZone CryptoCell 310 (default) by adding the following to your board DT file (or in an overlay):

	chosen {
		zephyr,entropy = &rng;
		};

This accounts for about 400 ms of the startup time according to the thread here:  High Current 400ms+ Startup Delay BLE Beacon Using RC Oscillator 

What signature type have you selected for MCUBoot, RSA or ECDSA_P256?

Best regards,

Vidar

[Yeccc]

Thank you for your help.
RNG is set by default in the nrf52840dk_nrf52840.overlay.

And the signature type is ECDSA_P256, it's also set by default on the nrfConnect SDK of 2.1.1 version.

We expect the startup time to be reduced to 500ms,

this is very important for our bulb product. Please help solve it as soon as possible. Thanks a lot.

# MCUBoot settings
#
# CONFIG_SINGLE_APPLICATION_SLOT is not set
# CONFIG_BOOT_SIGNATURE_TYPE_NONE is not set
# CONFIG_BOOT_SIGNATURE_TYPE_RSA is not set
CONFIG_BOOT_SIGNATURE_TYPE_ECDSA_P256=y

[Yeccc]

Thanks for your support.

Does this have any other impact?

[Yeccc]

Could you confirm it?
Does this modify have other effects?

[Vidar Berg]

Which configuration did you want to use, the one with LFXO or LFRC? 

[Yeccc]

The first configuration, it seems to reduce more startup time.
Does this modify have other effects?

[Vidar Berg]

I cannot think of any major drawbacks with selecting RCOSC clock source for this application. The average sleep current will increase slightly since the RCOSC source requires periodic calibration against the HFXO source (~1.5 uA), but I assume the bulb is mains powered. The RCOSC is also less accurate as you can see from the el. spec. here: Low frequency RC oscillator (LFRC).