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Default RF, Wifi

This example enables WiFi in a way that it's turned on in setup(), every time the device wakes up from sleep.

This can be used to i.e. sleep for a larger amount of time (say 5 minutes), measure something, connect to WiFi, send values off to some backend and go to sleep again. For testing purposes the sleep amount is set to 5 seconds.

We're using RF_DEFAULT as the parameter to deep sleep, so the RF unit is kept active during sleep:

  ESP.deepSleep(num_seconds_to_sleep * 1000000, RF_DEFAULT);

That works, but does consume power during sleep.

--- Miniterm on /dev/cu.SLAB_USBtoUART  9600,8,N,1 ---
--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
..........................ip:172.20.10.12,mask:255.255.255.240,gw:172.20.10.1
in loop()
We're connected, do something with wifi..
deep sleep, num_seconds=5
state: 5 -> 0 (0)
rm 0
del if0
usl
 �N?�$�¶␖��␔␡saQ��4�����)
f r0, ..scandone
state: 0 -> 2 (b0)
state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 1
cnt
.
connected with ThingforwardWiFi, channel 1
dhcp client start...
..................................................................ip:172.20.10.12,mask:255.255.255.240,gw:172.20.10.1
in loop()
We're connected, do something with wifi..

ESP8266 supports RF_DISABLED which effectively turns of all RF functionality, and consumes much less power. Unfortunately, changing RF_DEFAULT to RF_DISABLED breaks the sketch:

We're connected, do something with wifi..
deep sleep, num_seconds=5
state: 5 -> 0 (0)
rm 0
del if0
usl
 �N?�$�¦␖��␔OC␌A��4�����)
f r0, ..scandone
no ThingforwardWiFi found, reconnect after 1s
.reconnect
f 0, .error: pll_cal exceeds 2ms!!!
.error: pll_cal exceeds 2ms!!!
.error: pll_cal exceeds 2ms!!!
.error: pll_cal exceeds 2ms!!!
error: pll_cal exceeds 2ms!!!
..error: pll_cal exceeds 2ms!!!
error: pll_cal exceeds 2ms!!!
.error: pll_cal exceeds 2ms!!!

Device wakes up after deep sleep, but in setup() our calls to WiFi.begin() etc. fail because RF is still disabled. Blog posts state that after a ESP.deepSleep(... RF_DISABLED) another call to `ESP.deepSleep(..., RF_DEFAULT) is necessary.

This sounds easy, but the second call to ESP.deepSleep with RF_DEFAULT again puts the device to sleep. So when waking up, we need to know wether the last call to ESP.deepSleep has been made with RF DISABLED or RF DEFAULT. We're going to use the EEPROM stuff for that.