CircuitPython example for Espressif ESP-NOW protocol

espnow_receiver.py

# SPDX-FileCopyrightText: 2023 anecdata
#
# SPDX-License-Identifier: MIT

import time
import traceback
import supervisor
import os
import rtc
import espnow
import espidf
import wifi
import socketpool
import adafruit_ntp

from sekrets import *


#### ESPNOW Receiver
TZ_DEFAULT = -5
SNDR_CH = 0  # channel 1 (unless connected to an AP or acting as an AP)


def struct_time_to_iso_time():
    st = time.localtime()
    tz = TZ_DEFAULT
    return f"{st[0]:04d}-{st[1]:02d}-{st[2]:02d}T{st[3]:02d}:{st[4]:02d}:{st[5]:02d}{tz:+03}:00"

def connect():
    try:
        wifi.radio.connect(os.getenv("WIFI_SSID"), os.getenv("WIFI_PASSWORD"), bssid=AP_BSSID)  # use AP on channel <> 1
        time.sleep(1)  # wait for ap_info
        print(f"{struct_time_to_iso_time()} ipv4={wifi.radio.ipv4_address} channel={wifi.radio.ap_info.channel} rssi={wifi.radio.ap_info.rssi}")
    except ConnectionError as ex:
        traceback.print_exception(ex, ex, ex.__traceback__)

def ntp_to_rtc():
    wifi.radio.enabled = True
    connect()
    try:
        ntp = adafruit_ntp.NTP(pool, tz_offset=TZ_DEFAULT)
        rtc.RTC().datetime = ntp.datetime
        print(f"{struct_time_to_iso_time()} RTC time set with NTP time")
    except Exception as e:
        traceback.print_exception(e, e, e.__traceback__)
    wifi.radio.enabled = False  # lose the wifi channel


time.sleep(3)  # wait for serial
print(f"{'='*25}")
pool = socketpool.SocketPool(wifi.radio)
ntp_to_rtc()

peers = [espnow.Peer(mac=SNDR_MAC, lmk=SNDR_LMK, encrypted=True, channel=SNDR_CH),]
while True:
    with espnow.ESPNow() as e:
        e.set_pmk(RCVR_PMK)

        peers_report = ""
        for peer in peers:
            e.peers.append(peer)
            peers_report += f"mac={peer.mac} lmk={peer.lmk} ch={peer.channel} if={peer.interface} enc={peer.encrypted}\n"

        print(f"{'-'*25}\n{struct_time_to_iso_time()} Receiving...", end=" ")
        while True:
            if e:
                try:
                    packet = e.read()
                    print(f"{packet}")
                    break
                except ValueError as ex:  # Invalid buffer
                    traceback.print_exception(ex, ex, ex.__traceback__)
                    supervisor.reload()
                    break
        print(f"send=[{e.send_success} {e.send_failure}] read=[{e.read_success} {e.read_failure}] buf={e.buffer_size} phy={e.phy_rate} peers={peers_report}", end="")

It can typically take up to several milliseconds for e.send_success and e.send_failure to become valid. One way to handle that:

    try:
        e.send(f"{struct_time_to_iso_time().encode()}")

        delivery_time = 0
        start = time.monotonic_ns()
        while not e.send_success and not e.send_failure:
            if (delivery_time := time.monotonic_ns() - start) > SEND_TIMEOUT:
                break

Needs some parameter validation?

Adafruit CircuitPython 8.1.0-beta.0-80-g22636e056 on 2023-03-29; Adafruit Feather ESP32-S2 TFT with ESP32S2
>>> import time
>>> import espnow
>>> from sekrets import *
>>> 
>>> RCVR_CH = 0 
>>> 
>>> e = espnow.ESPNow()
>>> e.set_pmk(SYS_PMK)
>>> peer = espnow.Peer(mac=RCVR_MAC, lmk=LMK_181, encrypted=True, channel=RCVR_CH)
>>> e.peers.append(peer)
>>> 
>>> e.send(f"{'#'*250}")
>>> time.sleep(0.1)  # delivery confirmation takes non-zero time
>>> print(f"send=[{e.send_success} {e.send_failure}] read=[{e.read_success} {e.read_failure}]")
send=[1 0] read=[1 0]
>>> 
>>> e.send(f"{'#'*251}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
espidf.IDFError: ESP-NOW error 0x306a
>>> time.sleep(0.1)  # delivery confirmation takes non-zero time
>>> print(f"send=[{e.send_success} {e.send_failure}] read=[{e.read_success} {e.read_failure}]")
send=[1 0] read=[1 0]
>>> 
>>> e.send(f"{'#'*250}")
>>> time.sleep(0.1)  # delivery confirmation takes non-zero time
>>> print(f"send=[{e.send_success} {e.send_failure}] read=[{e.read_success} {e.read_failure}]")
send=[2 0] read=[1 0]
>>> 

For ease of navigation...
Original Issue: adafruit/circuitpython#3999
Original PR: adafruit/circuitpython#7470
Issue filed for above comments: adafruit/circuitpython#7903

Thanks for compiling/sharing this @anecdata 🥇 I hadn't seen the micropython notes on esp-now.

• Best results when wifi is disabled (wifi.radio.enabled = False) when not in use (requiring re-connection), and ESP-NOW is deinited when not in use (but see below). ESP-NOW docs suggest that wifi and ESP-NOW sending should work simultaneously on the same channel. ESP-NOW receiving may suffer from wifi power save modes (see https://micropython-glenn20.readthedocs.io/en/latest/library/espnow.html#espnow-and-wifi-operation thanks, @hopkapi). Sender and receiver must use the same phy_rate, PMK, LMK, channel, and encryption.

Updated link from Archive.org for micropython-espnow power related operation notes:
https://web.archive.org/web/20230520021624/https://micropython-glenn20.readthedocs.io/en/latest/library/espnow.html#espnow-and-wifi-operation

Thanks for the updated link @tyeth. CircuitPython does power management slightly differently adafruit/circuitpython#6976 which I think reduces complexity for ESP-Now. Channel I think is still a challenge to manage for now.

The sender example does not run on circuitpython 9.1.4 on a Waveshare ESP32-S3-Zero. I get several error messages (example : "ImportError: no module named 'sekrets'"). Is this expected behavior? Should I try this on circuitpython 8 instead?

@stanelie That was a file I used but didn't publish for the encryption keys, etc. (see the all-caps constants in the code, like RCVR_MAC and RCVR_LMK). You can put them anywhere you like and import them how you like.

Do you have examples of how this data should be formatted? For example, the mac address should be AB:CD:EF:GH:IJ or something like ['0x24', '0xec', '0x4a', '0x26', '0x8d', '0xb0'] ?

oh yeah, good question, PMK and LMK are bytes (or, ReadableBuffer), e.g., b'shufyrgetsfdtfyg'
https://docs.circuitpython.org/en/latest/shared-bindings/espnow/index.html#espnow.Peer
https://docs.circuitpython.org/en/latest/shared-bindings/espnow/index.html#espnow.ESPNow.set_pmk
Similarly, MAC address like b'\x00\x1A\xDD\x17\xC2\xA5' (or any equivalent form)
https://docs.circuitpython.org/en/latest/shared-bindings/espnow/index.html#espnow.ESPNowPacket.mac

Thanks!

How about setting the data rate for long range?
The doc says "espnow.ESPNow(buffer_size: = 526, phy_rate: int = 0), but I don't see what 0 means (1mbps? 56mbps?)
The values in the reference https://docs.espressif.com/projects/esp-idf/en/release-v4.4/esp32/api-reference/network/esp_wifi.html#_CPPv415wifi_phy_rate_t are not integer values, as expected by the Circuitpython library.

@stanelie it's an enumeration, so increasing integer values
https://github.com/espressif/esp-idf/blob/a9d0f22193acdf47a5a4db36832ae7068818962b/components/esp_wifi/include/esp_wifi_types.h#L594
the default is 0 (1Mbps), but you can change it

Thanks. Is there a better place for my questions than this thread?

I've tried all the phy_rate values between 0 and 32, and 16 and up do not work. So, I am unable to select the 31 or 32nd values (lora 250 and lora 500) that I want to enable long range. Where should I file a bug report about this issue?

(adafruit/circuitpython#9790)