ESP-NOW: Difference between revisions

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-ESP-NOW is a simple protocol that uses the ESP's WiFi radio (It coexists with the WiFi stack, also if active),
+ESP-NOW is intended as for ESP-to-ESP communication, based on WiFi but not requiring association.
-meaning it works regardless of there being an AP involved.
+It lets ESP devices send (small, unACKed) packets to other ESP devices
+: directly (without an AP)
+: coexisting with the regular WiFi stack (but there are practical footnotes)
- also meaning
+Some explanations mention that you pair with a peer,
+and will automatically recover after restart.
-Some explanations mention that you pair with a peer, after which it 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,
-...which seems to be a nice way of saying "you need to send to a specific MAC you have to know and will probably hardcode"
+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:
-- it will use the same channel as WiFi, so _follow_ that if you switch to a specific AP, probably not what you want
+* it will use the same channel as WiFi
-- different peer limits exist in Station mode and in AP mode or AP+Station mode
+:: so if you switch to a specific AP, ESP-now will _follow_ that, which probably not what you want
-- can't receive if in modem sleep.
-  - You might want to do do an occasional poll to something central-and-powered.
-- you will receive whatever is sent to you.
-  - You need to figure out that message is for your type of device,
-  - and that it is a type of message you want to respond to
-- no encryption in a practical sense
-- Fire-and-forget - No ACKs (like UDP-like).
+* Fire-and-forget - No ACKs
-- Assume the sending rate is no faster than 1Mbps
+* 250 bytes of payload, because it uses Action Frames
-- Up to 250 byte payload (at a time).
-- power savings
-  - (when AP is connected, will it effectively get TIM??)
-  - there are some other things in STA mode, see e.g. esp_now_set_wake_window()
+* 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
-adds peer (by MAC)
+* Assume the sending rate is no faster than 1Mbps ''at best'' but usually slower.
-send data
+* 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
-This makes it useful for ESP-to-ESP communication
+* no encryption in a practical sense
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ESP-NOW: Difference between revisions

Revision as of 14:38, 22 June 2024

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