nRF52840 startup time

RE: nRF52840 startup time

jeppe86 — Tue, 21 Dec 2021 08:14:44 GMT

Hi again Simon,

I'm only interested in the time between VDD on to CPU execute, so that is what I am focusing on.

The project was already in Release configuration, now I have changed the optimization level to level 2 (speed). Then I'm connecting 3.3V to P21 (External supply) and VIN on P20. The startup time (from VDD 1.8 V to GPIO high) is then 5.7 ms:

I think this is fast enough.

Best regards,

Jesper

RE: nRF52840 startup time

Simonr — Thu, 16 Dec 2021 12:52:52 GMT

Hi again Jesper

Do you have pin reset enabled? If so, can you measure the time to wake up there? The time from OFF to CPU execute accoridng to the product specification should only be 16.5us, se the Device startup times in the PS for more details.

What might cause this is that your device is in debug mode. Please try power cycling your device entirely before doing this test to see if the startup is quicker that way. You can also try optimizing the application for speed in the optimization levels setting in SES.

Best regards,

Simon

RE: nRF52840 startup time

jeppe86 — Wed, 15 Dec 2021 13:42:40 GMT

Hi Simon,

Thanks for your quick response. Here is the answers to your questions:

Yes, the board ist powered with 3.3V from a power supply. I'm connecting to the "External supply" on the board, marked P21 in the User Guide.
I'm using nRF5_SDK_17.1.0_ddde560. My project is based on the example project "examples\peripheral\blinky\pca10056\blank\ses".
Yes, this is from system off. Then I'm measuring the time from supply voltage on until GPIO high.

Looking forward to hear from you again!

Best regards,

Jesper

RE: nRF52840 startup time

Simonr — Wed, 15 Dec 2021 13:30:26 GMT

Can you provide some more information on the following:

Confirm that you power the board with ~3.3V (seems like it from your screen shot).
What SDK are you using here? The nRFConnect SDK will use a bit more time than the nRF5 SDK before it reaches main I think. What sample project is your project based on?
Can you also confirm that this if from system OFF until it sets the GPIO high or if it is from some idle mode?

Best regards,

Simon