Q: Clarification of BLE power consumption & plans to fix/improve; specific request for one feature

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Joined: Tue Nov 13, 2018 1:30 am

Q: Clarification of BLE power consumption & plans to fix/improve; specific request for one feature

Postby DrTune » Thu Nov 15, 2018 3:48 pm

Hi there,
Use case is lipo-powered continuous BLE advertising/connectable at typical a interval (e.g. 250ms), with a full wake-up when a BLE peripheral (phone) connects; like many users we wish to replace separate BLE+Wifi chips with an ESP32.

My understanding is that
a) ESP32 power consumption in anything other than Deep Sleep is considerable (several milliamps, e.g. ~100x an NRF51)
b) Deep Sleep loses all ram contents except the 8k RTC, and the current BLE library doesn't support that
c) It's possible to implement a wakeup stub in RTC RAM that is executed by the ROM very quickly after coming out of DS. Currently the linker reserves 4k (?) for future use by Espressif driver (logically to support radio modes where cpu goes to DS), and there's a bunch of ROM functions to drive the radio so a radio-handling DS wake stub seems reasonable. Hopefully the radio hardware doesn't take too long to spin up.
d) It seems less likely that anyone will implement a working BLE stack that can support deep sleeping _during_ a BLE connection - so power consumption when connected will likely always be orders of magnitude higher than other chips... but that's ok for many use cases (Beacons or only occasionally connected devices).
e) So, if we narrow the goal down to "implement a low power BLE advertising mode that boots the main app when a connection is accepted" it seems pretty reasonable... it's not something the community can implement b/c we don't have enough information on the radio, at least without REing the current code.

So: if this is the case, Dear Espressif, can we have a timeline for that? I need to make a decision on using ESP32 in a product and if we can't advertise BLE with low power it's a deal-breaker.


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