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Ethernet Over Serial Guide

Developed for Flashgate Technology Inc. and Provent Technologies Co.

Getting Started

We will use PPP (Point-to-Point-Protocol) to give a Variscite access to ethernet with only a serial connection.

Aliases

  • ‘host’: The Variscite that has access to ethernet via an Ethernet cable.
  • ‘device’: The Variscite that does not have access to ethernet.

Materials Needed

  • 2x Variscite SOM
  • 3x Jumper cable
  • 1x PC with Debian or Ubuntu installed - used for building Kernel
  • 1x 4gb or larger SD card
  • 1x SD card reader

Optional

  • 1x extra keyboard - for device Variscite
  • 1x extra monitor with HDMI in - for device Variscite

Kernel Modifications

At the time of writing, we are using Debian Jessie Release 2 - 4.1.15. By default, the Kernel does not have PPP enabled.

To enable PPP, we must rebuild the Kernel.

Part 1 - Building the New Kernel

The following commands were taken from the Variscite Wiki: http://variwiki.com/index.php?title=VAR-SOM-MX6_Debian_R2

(Assuming your machine is running Debian jessie, see wiki for Ubuntu packages if your machine is running Ubuntu)

Install required packages

sudo apt-get install -y binfmt-support qemu qemu-user-static debootstrap kpartx
sudo apt-get install -y lvm2 dosfstools gpart binutils git lib32ncurses5-dev python-m2crypto
sudo apt-get install -y gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath socat libsdl1.2-dev
sudo apt-get install -y autoconf libtool libglib2.0-dev libarchive-dev
sudo apt-get install -y python-git xterm sed cvs subversion coreutils texi2html bc
sudo apt-get install -y docbook-utils python-pysqlite2 help2man make gcc g++ desktop-file-utils libgl1-mesa-dev
sudo apt-get install -y libglu1-mesa-dev mercurial automake groff curl lzop asciidoc u-boot-tools mtd-utils

Deploy source

$ cd ~
$ git clone https://github.com/varigit/debian-var.git -b debian_jessie_varsommx6_var02 var_som_mx6_debian

Modify kernel configuration (part 1)

From "12 How-to: Modify kernel configuration"

cd ~/var_som_mx6_debian/src/kernel
sudo make ARCH=arm mrproper
sudo make ARCH=arm imx_v7_var_defconfig
sudo make ARCH=arm menuconfig

Enable PPP (Point-to-Point Protocol)

  • Navigate to Device Drivers
  • Navigate to Network Device Support
  • Go to everything PPP related and Press 'Y' so it has a (*) (should look similar to image below)
  • Save Kernel by using Arrow key -> Right until the bottom text hovers over (S)ave
  • Press Enter to Save. Do not fill out a name for the config file. Press enter again.
  • Exit the menu config

Point-to-Point Protocol Selected in Kernel

Modify kernel configuration (part 2)

From "12 How-to: Modify kernel configuration"

sudo make ARCH=arm savedefconfig
sudo cp arch/arm/configs/imx_v7_var_defconfig arch/arm/configs/imx_v7_var_defconfig.orig
sudo cp defconfig arch/arm/configs/imx_v7_var_defconfig

Build the kernel

Do NOT run the commands in "4.1 Build all". It will overwrite the config you just modified.

Run all commands in "4.2 Build by parts"

cd ~/var_som_mx6_debian
./make_var_som_mx6_debian.sh -c bootloader
./make_var_som_mx6_debian.sh -c kernel
./make_var_som_mx6_debian.sh -c modules
./make_var_som_mx6_debian.sh -c rootfs
./make_var_som_mx6_debian.sh -c rtar

Create boot SD card

  1. Plug SD card into machine
  2. Run fdisk -l to find where the SD card is fdisk -l output
  3. Outlined in red is my SD card. It is at /dev/sdd
  4. Run command below but replace /dev/sdX with your SD card location (e.g. /dev/sdd)
./make_var_som_mx6_debian.sh -c sdcard -d /dev/sdX

Done

You have an SD card with the Point-to-Point Protocol enabled.

  • Plug the SD card into the Variscite MX6 Custom board.
  • Hold the middle button and switch the power on
  • The board will boot from the SD card

Optional - Flash SD card to internal memory (eMMC)

While logged into the Variscite (user: linaro pass: linaro) run the following commands:

sudo su
debian-install.sh -b mx6cb -t res

Part 2 - Physical Set Up

The 2 Variscites must be connected over Serial.

In the end the set up will look similar to this:

2 Variscites Connected By Serial

The pin-out for the default RS232 sourced from https://www.variscite.com/wp-content/uploads/2017/12/VAR-MX6CustomBoard-Datasheet.pdf:

RS232 Serial Pin Out

Following the pin-out:

  • RX = pin 2
  • TX = pin 3
  • GND = pin 5

Wire the host and device together

  • Connect RX (host) -> TX (device)
  • Connect TX (host) -> RX (device)
  • Connect GND (host) -> GND (device)

Part 3 - Connect

Now that the Kernel is ready and the two Variscites are physically connected, it is time to share the ethernet connection.

Enable ip forwarding on the host

  1. On the host Variscite (the one with ethernet) and run these commands:
sudo su
apt-get install -y nano
nano /etc/sysctl.conf
  1. Find this line:
#net.ipv4.ip_forward=1
  1. Uncomment the line by removing the '#' at the start.
  2. Save and exit by pressing CTRL+X then pressing Y.

Connect: host

On the host Variscite, run this command:

pppd -d noauth nocrtscts xonxoff passive local maxfail 0 nodetach 192.168.10.18:192.168.10.19 persist proxyarp /dev/ttymxc2 38400

Connect: device

Using a keyboard and monitor attached to the device Variscite, run this command:

pppd -d noauth nocrtscts xonxoff passive local maxfail 0 defaultroute persist nodetach 192.168.10.19:192.168.10.18 /dev/ttymxc2 38400

Test

  • Try pinging the device
ping 192.168.10.18
  • Try ssh'ing into the device
ssh [email protected]

Making changes

  • Change IP address
    • Switch 192.168.10.18 and 192.168.10.19 to new IP addresses.
    • NOTE: They must not be used by any other device.
  • Change baud rate
    • Change 38400 to new baud rate, e.g. 152000
  • Change tty
    • Switch /dev/ttymxc2 with other terminal, e.g. ttyS0

Debugging

  • Error running pppd:
Peer refused to agree to our IP address
Connect time 0.1 minutes.
Sent 2650 bytes, received 2650 bytes.
sent [IPCP TermReq id=0xcc "Refused our IP address"]
rcvd [IPCP TermReq id=0xcc "Refused our IP address"]
sent [IPCP TermAck id=0xcc]
rcvd [IPCP TermAck id=0xcc]
sent [LCP TermReq id=0x3 "No network protocols running"]
rcvd [LCP TermAck id=0x3]
Connection terminated.

Solution: IP Addresses do not match or are already in use. Check the IP Addresses in the pppd command.

Original Reference

“Share Internet to the Raspberry Pi Zero” - The Magpi Magazine, 2016 https://www.raspberrypi.org/magpi/share-internet-to-the-raspberry-pi-zero/