ESP-NOW

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

ESP-NOW is intended as for ESP-to-ESP communication, based on WiFi but not requiring association (it abuses action frames).

It lets ESP devices send small packets to other ESP devices

directly (without an AP)

coexisting with the regular WiFi stack (but there are practical footnotes)

Some explanations mention that you pair with a peer, and will automatically recover after restart.

...which seems to be a fancy way of saying that it's stateless, that you need to send to a specific MAC, that you have to know and will probably either hardcode or somehow discover"

There is also a note that you can actually use broadcasts, in which case you don't have a peer limit.

Limitations:

• will use the same channel as WiFi

so if you switch to a specific AP, ESP-now will _follow_ that, which is often not may not be predictable

• Fire-and-forget - No ACKs

• 250 bytes of payload, because it uses Action Frames

• can't receive if in modem sleep
  • note: it can make sense to have one ESP stay awake and have others poll it between sleep, though at this point it's not too differrent from that being a real AP - in fact might you get TIM on a real AP)
  • there are some other things in STA mode, see e.g. esp_now_set_wake_window()

• different peer limits exist in Station mode and in AP mode or AP+Station mode

• Assume the sending rate is no faster than 1Mbps at best but usually slower.

• you will receive whatever is sent to you.
  • You need to figure out that message is for your type of device,
  • and/or whether it is a type of message you want to respond to

• no encryption in a practical sense