High power and delay before associating with secure AP

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High power and delay before associating with secure AP

Postby tvoneicken » Mon Nov 26, 2018 8:34 pm

I am testing the speed at which the esp32 can associate with a secured AP after coming out of deep-sleep. I notice that after probing for the AP the esp32 spends about 700ms with an elevated power consumption but no communication. Can you explain what is happening? It is particularly curious to me that this happens before the first association packet, which is at a time where there is no crypto to be performed since the 4-way EAPOL key exchange is yet to happen. You can see this period marked as "crypto?" in the scope trace below where the blue trace shows power consumption coming out of deep-sleep and ending in transmitting some data to a TCP server.
esp32-deep-sleep-secure-mode-3-all-annot.png (71.82 KiB) Viewed 214 times
The exact same code used on an open AP does not incur this period of elevated power consumption (note the 50ms/div here vs. 200ms/div above):
esp32-deep-sleep-open-mode-3-all-annot.png (85.75 KiB) Viewed 214 times
Thank you!

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