k210-sdk-stuff/linux

esptun

A tool to tunnel IP packets over UDP over WIFI through an UART connected to a ESP8285 with the standard AT firmware.

Usage

esptun <ifname> <uart> <ssid> <passwd> <host> <port>

This will create tun interface ifname. Then, with the with the ESP WIFI device on uart it connects to the AP ssid with password passwd. It creates a UDP over IP tunnel with the other endpoint host:port.

The new tun device will not be configured, use the ip utility to assign an IP address and switch the interface on.

For example:

/root/esptun tun0 /dev/ttyS1 "accesspointname" "secretpassword" 192.168.122.21 23232
/sbin/ip addr add 10.0.1.2/24 dev tun0
/sbin/ip link set tun0 up
/sbin/ip route add default via 10.0.1.1 dev tun0

Host side

On the other endpoint the tunnel is expected to be a host running socat or similar to unwrap the tunnel. For example:

sudo socat UDP:192.168.2.127:23232,bind=192.168.122.21:23232 \
    TUN:10.0.1.1/24,tun-name=tundudp,iff-no-pi,tun-type=tun,su=$USER,iff-up

Optionally, enable forwarding and masquerading:

sudo iptables -t nat -F
sudo iptables -t nat -A POSTROUTING -o ens3 -j MASQUERADE
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward

Linux kernel

Until there is a proper solution, you can use the following kernel branch to get the UART working on Kendryte K210 under Linux:

https://github.com/laanwj/linux/tree/kendryte-5.6-rc1-wifi

This is a hack that configures the FPIOA and GPIOHS manually, and configures UART1 from the device tree.

To enable TUN/TAP, enable the following kernel settings:

CONFIG_NET=y
CONFIG_INET=y
CONFIG_TUN=y

While building the root filesystem, make sure you enable at least ip and ping (and possibly other network tools) for busybox.

Author

Copyright (c) 2020 W.J. van der Laan Distributed under the MIT software license,