ESP8266 wakeup from deep sleep: Both by timer and button? In a project powered by batteries, the ESP8266 should go to deep sleep for long time, having RF disabled. After some number of sleep cycles, it shall restart with RF enabled, synchronize time via NTP, and again go to sleep. Think this could work with a counter saved in RTC Memory or SPIFFS.
Additionally, s.o. should be able to wake up via push button (at any time), which should result in different behaviour (running as WiFi AP, allowing for configuration of new WiFi credentials).
The question is: Is it possible to find out what did wake the ESP (timer or pushbutton)?
Edit: Using external circuitry this might be possible. To avoid this, we switch to ESP32, which is an overkill for the project, but easy to find out the source of the wakeup (and with the possibility to use touch sensors). Additionally, ESP32 allows for easy use of &quot;Preferences&quot; in NVR and variables in RTC memory (when using the Arduino IDE), which will survive deep sleep (RTC) and even reset/power loss (NVR).
Place a capacitor on the ESP side of the button to one power rail or the other (my preference is to ground, but either should work), and have the setup() routine reads the state of the pushbutton switch as it's first instruction.  You probably don't even need the capacitor, but if you don't have it, you'll have to read the switch state multiple times to account for possible contact bounce.
If the ESP wakes up due to a timer, there will be no activity on the PB line; if it wakes up due to the PB being pressed, there will be activity on the PB line for several 10's of millisec no matter how quickly it is pressed and released.