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Wladimir J. van der Laan a241403058 linux: Add note about esptun baudrates		2020-02-22 15:01:08 +00:00
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.gitignore	Add k210 linux utilities	2020-02-21 15:42:04 +00:00
esptun.c	linux: Optimize binaries for size	2020-02-22 14:37:06 +00:00
Makefile	linux: Optimize binaries for size	2020-02-22 14:37:06 +00:00
README.md	linux: Add note about esptun baudrates	2020-02-22 15:01:08 +00:00
term.c	linux: Set timeout argument on poll() properly	2020-02-22 12:22:25 +00:00

README.md

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 link set dev tun0 mtu 1472
/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

(setting the MTU to 1500-20-8 the typical network MTU minus IP and UDP header overhead, because otherwise the ESP's network stack will drop the oversized packets)

Baudrate note

If the tunnel hangs intermittently, the problem may be the BAUDRATE setting. The ESP8285 can handle baudrates up to 115200*40 = 4608000 baud and esptun will try switching to a higher baudrate.

However, these higher baudrates are unstable as it seems that the UART cannot keep up reading in some cases and loses data. This may be a misconfiguration or something that could be improved in the 8250_dw Linux driver for this peripheral (DMA support?).

Which values work may vary, if you want to be completely safe use 115200. The value can be changed at the top of esptun.c.

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 &
sudo ip link set dev tundudp mtu 1472

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