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esp_slip_router

A SLIP to WiFi router

This is an implementation of a SLIP (Serial Line IP - RFC1055) router on the ESP8266. It can be used as simple (and slow) network interface to get WiFi connectivity. The ESP can act as STA or as AP. It transparently forwards any IP traffic through it. As it uses NAT no routing entries are required on the other side.

Docker implementation

The dockerized build environment have been made to build latest and/or modified firmware without worrying about esp-open-sdk build process, all required libs already included to ease the build process of the firmware, you can now simply write:

make build_latest

You can also enter the built environment by issuing command:

make enter

To flash using inside docker tools you can write:

make flash_latest /dev/ttyUSB0

TODO

Client guides

Usage as STA

In this mode the ESP connects to the internet via an AP with ssid, password and offers at UART0 a SLIP interface with IP address 192.168.240.1. This default can be changed in the file user_config.h.

To connect a Linux-based host, start the firmware on the ESP, connect it via serial to USB, and use the following commands on the host:

sudo slattach -L -p slip -s 115200 /dev/ttyUSB0&
sudo ifconfig sl0 192.168.240.2 pointopoint 192.168.240.1 up mtu 1500

now

telnet 192.168.240.1 7777

gives you terminal access to the esp as router. On the ESP you then enter:

CMD>set ssid <your_ssid> 
CMD>set password <your_pw> 
CMD>set use_ap 0
CMD>save
CMD>reset

To get full internet access you will need aditionally a route:

sudo route add default gw 192.168.240.1

and a DNS server - add an appropriate entry (e.g. public DNS server) in /etc/resolv.conf, eg. by (as root):

echo "nameserver 9.9.9.9" > /etc/resolv.conf

A script may help to automize this process.

The status LED (default: GPIO2) indicates:

The default config of the router can be overwritten and persistenly saved to flash by using a console interface. This console is available via tcp port 7777 (e.g. from the host attached to the serial line - see above).

The console understands the following command:

If you want to enter non-ASCII or special characters you can use HTTP-style hex encoding (e.g. "My%20AccessPoint") or, only on the CLI, as shortcut C-style quotes with backslash (e.g. "My\ AccessPoint"). Both methods will result in a string "My AccessPoint".

Usage as AP

You can also turn the sides and make the ESP to work as AP - useful e.g. if you want to connect other devices to a RasPi that has no WiFi interface:

With a Linux-based host start the firmware on the esp, connect it via serial to USB, and use the following commands on the host:

sudo slattach -L -p slip -s 115200 /dev/ttyUSB0&
sudo ifconfig sl0 192.168.240.2 pointopoint 192.168.240.1 up mtu 1500
sudo route add -net 192.168.4.0/24 gw 192.168.240.1

again

telnet 192.168.240.1 7777

gives you terminal access to the ESP as router. On the ESP you then enter:

CMD>set ap_ssid <your_ssid> 
CMD>set ap_password <your_pw> 
CMD>set use_ap 1
CMD>save
CMD>reset

Now STAs of this AP get IP adresses in the 192.168.4.0/24 network and can reach the Linux machine as "192.168.240.2". The AP interface is NATed, i.e. you cannot set up connections from the Linux machine to the STAs, but from STAs to Linux works. Useful e.g. if you want to reach an MQTT server on the Linux.

The console understands the following command for the AP mode:

Building and Flashing

To build this binary you download and install the esp-open-sdk (https://github.com/pfalcon/esp-open-sdk). The software was developed and tested usinfg NONOS SDK v2.2. Make sure, you can compile and download the included "blinky" example.

Then download this source tree in a separate directory and adjust the BUILD_AREA variable in the Makefile and any desired options in user/user_config.h. Build the esp_wifi_repeater firmware with "make". "make flash" flashes it onto an esp8266.

The source tree includes a binary version of the liblwip_open plus the required additional includes from my fork of esp-open-lwip. No additional install action is required for that. Only if you don't want to use the precompiled library, checkout the sources from https://github.com/martin-ger/esp-open-lwip . Use it to replace the directory "esp-open-lwip" in the esp-open-sdk tree. "make clean" in the esp_open_lwip dir and once again a "make" in the upper esp_open_sdk directory. This will compile a liblwip_open.a that contains the NAT-features. Replace liblwip_open_napt.a with that binary.

If you want to use the precompiled binaries you can flash them with "esptool.py --port /dev/ttyUSB0 write_flash -fs 32m 0x00000 firmware/0x00000.bin 0x10000 firmware/0x10000.bin" (use -fs 8m for an ESP-01).

For Wemos D1 Mini use the following flash command:

esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash -fs 4m -fm dio 0x00000 firmware/0x00000.bin 0x10000 firmware/0x10000.bin

Softuart UART

As UART0, the HW UART of the esp8266 is busy with the SLIP protocoll, it cannot be used simultaniuosly as debugging output. This is highly uncomfortable especially during development. If you define DEBUG_SOFTUART in user_config.h, a second UART will be simulated in software (Rx GPIO 14, Tx GPIO 12, 19200 baud). All debug output (os_printf) will then be redirectd to this port.

Known Issues