Wi-Fi light sleep periodically waking up longer than expected

[gerdiman1]

Hi,
We’re building a custom app using ESP8266 that requires Wi-Fi light sleep to work properly but encountering issues with the system waking up periodically for longer than expected and blowing up our power budget.

There two unknown events that wake up the system periodically (see images below):

1. Periodic wake-up with radio transceiver on every approximately every 1.8s

2. Periodic scheduled task wake-up approximately every 3 seconds. The system stays in modem sleep instead of entering light sleep.

These current plots were measured on ESP8266 running a custom app that enables light sleep, connects to an access point (AP) and then remains idle. The DTIM interval of the AP is 3. I have made sure that there’s no timer running in our app, but we’re still seeing unknown wake-up events. Can you shed some lights on what these events might be?

Thanks.

[Her Mary]

According to the documentation http://www.espressif.com/sites/default/files/documentation/9b-esp8266-low_power_solutions_en.pdf, it seems to be the router TIM and the application(or system) timer.

[gerdiman1]

Your reply is very misleading and incorrect. TIM is sent every beacon. DTIM is sent typically every 1 or 3 beacons. In the case above, DTIM are the periodic spikes you see roughly every 300ms. My concerns are clearly indicated in the figures above and the document you provided doesn't address those concerns. If there are system timer running, what are those timers? Why can't the RTC timer be used to wake up the CPU when the timer is due instead of idling and wasting energy? Can someone in Espressif that knows the code answer this question? Thanks.

[gerdiman1]

This same exact issue I'm seeing. viewtopic.php?f=7&t=3184&p=18308#p18308

[pscholl@bawue.de]

I do have the same issue as well, fiddling with the DTIM or beacon interval only worsens the issue. Using SDK 2.2.

with BI 100ms, DTIM 4

with BI 100ms, DTIM 20

with BI 200ms, DTIM 10

Could this be an issue with Beacon Interval synchronization, i.e. the module is loosing sync to the BI and needs to stay in RX mode to make sure not to miss the next beacon? This is a rather grave issue, as it renders the light sleep mode mostly ineffective.