Project

There is a Raspberry Pi Pico Board on the market called PICO-W that uses the ESP8285 wifi chip instead of the Infineon CYW43439. This is a problem because pre-built wifi libraries for PICO-W won't work.

Goal

I tried to create a simple Python library to be able to use the wifi part of the board. The inspiration for the API was the API that is used in Arduino.

Project Status

The project is by no means in production state. Youcan consider it as a proof of concept. Nevertheless I tried to make it functional and useful.

The project consists of two Python files - one for the API and one for the driver. You can use the API to join the wifi network, connect to the TCP/SSL server and communicate with the server.

On the ESP8285 side, an AT-interpreter must be installed. You can use the official one from Espressif or you can use another one from independent projects. I use my code https://github.com/JiriBilek/ESP_ATMod because it can connect to servers using TLS1.2.

I could complete the project with all the bells and whistles of the Arduino wifi library but I doubt it would be useful. It would fill PICO's memory with a Python code that is rarely used. So I focused on the basic functionality.

What Works Now

• join AP as a client (in ESP terminology "station"), DHCP only

• get information about the connection

• connect to TCP or SSL server

• send data to the server

• read data from the server

The Future

• enable fixed IP address and DNS

• discover and list AP's

• UDP support

• enable advanced TLS features like fingerprint validation, certificate chain validation etc.

• server support

• AP mode

Credits

The first idea came from the https://github.com/mocacinno/rp2040_with_esp8285 repository. I learned what I needed to do to make the wifi part of the board work.

The Arduino AT library I tried to port to Micropython was https://github.com/JAndrassy/WiFiEspAT. It is a library with a robust implementation of the communication with the ESP MCU.

Thanks guys.

Installation

1. Reflash ESP8285 Chip With AT Firmware

• unplug Pico from the USB, press the button near the USB-C connector (BOOTSEL) and plug it back while holding the button. In Explorer you should see a new disk drive called RPI-RP2.

• copy the file Serial_port_transmission.uf2 into this new drive. Now, the PICO works as a USB to serial converter.

• unplug the Pico from the USB, press the button near the Wifi chip (on my board it is called DOOT) and plug it back while holding the button. Now you have the ESP8285 in firmware download mode.

• download the AT command interpreter to the ESP8285. You can use any AT firmware for ESP8285 or ESP8266. I recommend using my firmware from the repository https://github.com/JiriBilek/ESP_ATMod. This firmware uses modern TLS ciphers required for TLS1.2.

  The Pico is now working as a USB to serial converter so that you will see it as a new COM port. Use this port for flashing. Choose one method:

  • if you are familiar with Arduino you can clone the repository above, compile the code and flash it into the ESP8255.

  • or use the pre-compiled AT firmware and esptool.exe from https://github.com/espressif/esptool/releases. Download the zip file, extract it and flash the firmware with the command:

    esptool --port <your com port> write_flash 0x0 ESP_ATMod.0.6.bin

  • or use the flash download tool from Espressif. Follow the instructions at https://github.com/mocacinno/rp2040_with_esp8285/blob/main/README.md.

  You can verify the firmware is running correctly by replugging the board, connecting a serial terminal (e.g. PuTTY) to the COM port on 115200 Bd and typing AT followed by Enter and Ctrl-J. The ESP8285 should respond OK.

2. Flash Micropython to the PICO-W

• bring the Pico into the download mode as you did at the beginning of this process (unplug - press BOOT - plug again).

• get the latest Pico firmware from https://micropython.org/download/RPI_PICO/. Don't use the firmware for Pico-W because you don't need the stuff for the CYW chip.

• flash the firmware by copying the uf2 file to the Pico disk drive.

3. Download the Library to the Pico W

• start Thonny on your computer, connect the Pico board and download the WiFi.py and EspAtDrv.py files to the board.

• Testing: in the wifitest.py file, set the SSID and PWD variables according to your network and run it from Thonny.

API

Import WiFi.py into your project and use the following API.

General Communication

Constants

WL_NO_SHIELD = const(255)
WL_NO_MODULE = WL_NO_SHIELD
WL_IDLE_STATUS = const(0)
WL_CONNECTED = const(1)
WL_CONNECT_FAILED = const(2)
WL_CONNECTION_LOST = const(3)
WL_DISCONNECTED = const(4)
WL_AP_LISTENING = const(5)
WL_AP_CONNECTED = const(6)
WL_AP_FAILED = const(7)

init(resetType: int) -> int

Initialize the wifi communication. Must be the first command in the application.

resetType: 0 - perform software reset, otherwise no reset

status() -> int

Get the wifi connection status.

begin(ssid: str, passphrase: str, bssid: bytearray = None)

Connect to the AP with the specified SSID and password. If the bssid parameter is specified, connect to the AP with that BSSID.

disconnect(persistent: int) -> int

Disconnect from the AP. When persistent, the wifi device will automatically reconnect on boot.

setPersistent(persistent: int) -> int

Set or get persistency of the newly created connections to APs. When persistent, the wifi device will automatically reconnect on boot.

rssi() -> int

Return current RSSI or None.

channel() -> int

Returns wifi channel or None.

localIp() -> str

Returns local IP address as string or None.

gatewayIp() -> str

Returns gateway address or None.

subnetMask() -> str

Returns subnet mask or None.

dnsIp(n: int = None)

n == None: Returns an array of DNS server addresses or None.
n != None: Returns n-th DNS server address or None.

Client

First, you need to get the wifi client object: WiFi.Client(). Then you can use its methods:

connect(host: str, port: int) -> int

Connect in TCP mode to host on port port. Returns True is successful.

connectSSL(host: str, port: int) -> int

Connect in SSL (TLS) mode to host on port port. Returns True is successful.

connected() -> int

Returns the state of the client. True means connected.

flush()

Flushes the output buffer to the server.

stop()

Flushes the output buffer to the server and stops the connection.

abort()

Aborts the connection.

print(data: str) -> int

Sends data to server. The data are internally buffered until available(), read(), readBuf() or flush() is called.

available() -> int

Returns the number of bytes in the input buffer. Flushes the output buffer first.

peek() -> int

If the input buffer is not empty, returns the first byte without discarding it. Otherwise returns -1.

read() -> int

Returns one byte from the input buffer. If the buffer is empty, returns -1.

readBuf(size: int) -> bytes

Returns at most size bytes from the input buffer. May return empty array.

Minimum example

import utime  
import WiFi  
  
WiFi.init(0)
WiFi.begin("<<YOUR SSID>>", "<<YOUR PASSWORD>>")
if (WiFi.status() == WiFi.WL_CONNECTED):
    cli = WiFi.Client()
    if (cli.connectSSL("www.example.com", "443")):
        cli.print("GET / HTTP/1.1\r\nHost: www.example.com\r\n\r\n")
        t = utime.ticks_ms()
        while (cli.available() == 0 and utime.ticks_ms() - t < 5000):  # timeout 5 s
            utime.sleep(0.01)
        resp = bytearray()
        while (cli.available()):
            b = cli.readBuf(cli.available())
            resp += b
            t = utime.ticks_ms()
            while (cli.available() == 0 and utime.ticks_ms() - t < 1000):  # timeout 1 s
                utime.sleep(0.01)
        print(resp)
    cli.stop()
WiFi.disconnect(False)