Boards for embedded Linux


In this post, I list some of the various boards that I have used, or known others to have used, with embedded Linux. Some are also suitable for hosting Android.

 

Other boards that I have used in the past but use sparingly now…

  • BeagleBoard-xM by TI
  • PandaBoard ES by TI

 

Posted in Android, ARM, Hardware, Linux

Add wireless to custom embedded Linux system for Raspberry Pi


Raspberry Pi does not have Wi-Fi on board. You’ll need to use a Wi-Fi dongle and discover the driver to build into the kernel. One way to find the driver is to plug the dongle into a Raspberry Pi running Raspbian, and perform an lsmod to see which module gets loaded. The following text assumes you’re building a custom embedded Linux system using Buildroot.

Kernel Configuration

Invoke the Kernel configuration utility using make linux-menuconfig.

Enable Wireless Networking support under Networking support

Wireless

Enable cfg80211 – wireless configuration API, and Generic IEEE 802.11 Networking Stack (mac80211), under Networking Support, Wireless

cfg80211 and mac80211

Enable EEPROM 93CX6 support under Device Drivers, Misc devices, EEPROM support. Required for RTL8187 module in my Wi-Fi dongle, may not be needed for your particular adapter

EEPROM 93CX6 support

Enable Wireless LAN driver support under Device Drivers, Network device support

Wireless LAN

Enable Realtek 8187 and 8187B USB support under Device Drivers, Network device support, Wireless LAN. Select the driver appropriate for your adapter

Realtek 8187 and 8187B USB support

Package Configuration

Invoke make menuconfig within the buildroot folder from a command prompt.

Select package iw required to configure wireless networking

iw

Select package wpa_supplicant and its sub-packages for WPA/WPA2 support

wpa_supplicant

Perform the build by invoking make, copy the newly minted system to an SD card, and use it to boot up your Raspberry Pi.

Configure Wireless Networking

List your wireless interfaces

iw list

Bring up the wlan0 interface

ifconfig wlan0 up

Find the access point you want to connect to

iw dev wlan0 scan

Assuming you’re using WPA/WPA2, invoke wpa_passphrase to create config file, and wpa_supplicant to connect to network

wpa_passphrase your_SSID your_passphrase > your_SSID.conf
wpa_supplicant -B -i wlan0 -c your_SSID.conf

Instead, if you want to connect to an open network

iw dev wlan0 connect your_SSID

Request IP address using DHCP

dhcpcd wlan0

Check link status

iw dev wlan0 link

Add nameserver entries to /etc/resolv.conf e.g.

nameserver 8.8.8.8
nameserver 8.8.4.4

Test internet connectivity using ping

ping www.google.com
Posted in Miscellaneous

Moto G 4G screen gone bad in less than a month of use


Besides the line artifacts on the screen, the display seems to be at a lower resolution, icons and fonts appear more pixelatedMoto G 4G screen gone bad

Just to be sure it was the screen and not the software, I took the screenshot below

Moto G 4G Screenshot

Unfortunately, I bought it on one of my U.S. trips. The local authorized service center will only service Moto G’s under warranty bought in Brazil. I didn’t even save any money buying it in the U.S. I’ll only buy Apple products when in the U.S. They’ve got an international warranty program.

Posted in Miscellaneous

Embedded Linux system for BeagleBoard-xM with Yocto Project


I’ve mostly abandoned a BeagleBoard-xM that I have, and am using Raspberry Pi for most of my embedded Linux hacks. I have built a Linux system for BeagleBoard-xM using Yocto Project though, so thought I’d put the instructions out there.

I’m performing the following build on an Ubuntu 14.04 Parallels Desktop 9 VM. The steps below were mostly discovered from the Yocto Project Quick Start. Look there if you need further help.

The following dependencies are required on the build machine before you proceed

sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath libsdl1.2-dev xterm

Next, clone the the dora branch from the git repo of Yocto Project, and prepare the build environment

git clone -b dora http://git.yoctoproject.org/git/poky
source poky/oe-init-build-env build

You’ll be in the the build folder when that is done.

Add the following to conf/local.conf

MACHINE ?= "beagleboard"

Go ahead and perform the build

bitbake core-image-minimal

After the build is done, grab and deploy the images from tmp/deploy/images/beagleboard.

Posted in ARM, Linux

Embedded Linux system for Raspberry Pi with Yocto Project


Yocto Project, and OpenEmbedded, have been making news lately as the toolchain to build custom embedded Linux systems. I decided to try and get a working Linux system up and running on a Raspberry Pi.

The procedure that follows uses the meta-raspberrypi BSP by David-John Willis, in tandem with Yocto Project poky.

Initialize the build by executing the following commands. I use an Ubuntu 14.04 VM with Parallels.

git clone http://git.yoctoproject.org/git/poky
git clone http://git.yoctoproject.org/git/meta-raspberrypi
git clone https://github.com/dv1/meta-gstreamer1.0.git
source poky/oe-init-build-env rpi-build
cd rpi-build

Append meta-raspberrypi and meta-gstreamer1.0 layers to BBLAYERS in conf/bblayers.conf. For example

BBLAYERS ?= " \
  /home/parallels/yocto/poky/meta \
  /home/parallels/yocto/poky/meta-yocto \
  /home/parallels/yocto/poky/meta-yocto-bsp \
  /home/parallels/yocto/poky/meta-gstreamer1.0 \
  /home/parallels/yocto/poky/meta-raspberrypi \
  "

Set MACHINE to raspberrypi in conf/local.conf. Complete the build by executing

bitbake rpi-hwup-image

That takes a while. After the build is complete, create an SD card with the following command. Remember to change /dev/sdb to the proper device name.

dd if=tmp/deploy/images/raspberrypi/rpi-hwup-image-raspberrypi.rpi-sdimg of=/dev/sdb

Boot Pi using the SD card. Command line output appears on the HDMI display, or the serial port on the expansion header. Login is root, with an empty password.

Posted in Raspberry Pi

Linux NAT router


This post documents the kernel modules and other packages required to build an embedded Linux NAT router using buildroot, for Raspberry Pi.

Modify Linux kernel configuration

Invoke make linux-menuconfig in buildroot folder to initiate kernel configuration utility. Select modules shown in the figures below.

Networking Options

Network packet filtering framework

Ensure that the following is enabled under Networking Options

  • Network packet filtering framework (Netfilter)

Core Netfilter Configuration

Ensure that the following are enabled under Core Netfilter Configuration

  • Netfilter connection tracking support
  • “conntrack” connection tracking match support
  • “state” match support

IP: Netfilter Configuration

Ensure following is enabled under Network packet filtering framework (Netfilter)

  • Advanced netfilter configuration

IPv4 packet filtering and NAT

Ensure the following modules are selected under IP: Netfilter Configuration

  • IPv4 connection tracking support (required for NAT)
  • IP tables support (required for filtering/masq/NAT)
  • Packet filtering
  • IPv4 NAT
    • MASQUERADE target support
    • NETMAP target support
    • REDIRECT target support

Enable other targets if you want to do sophisticated filtering.

Modify Buildroot Configuration

Include iptables utility package shown in the figure below, using the configuration utility invoked by executing make menuconfig. Include tcpdump if you want to sniff network data.

Buildroot iptables

Now, just execute make to build the system, and copy the kernel image and root file system to SD card.

Perform NAT routing

I use the following commands to bring up the network interfaces and setup NAT forwarding. Any packets received on interface eth0 are forwarded to usb0. Only packets for connections already established are forwarded back to eth0. usb0 is a USB CDC ethernet interface of the kind seen in modems.

ifconfig usb0 up
ifconfig eth0 up
dhcpcd
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o usb0 -j MASQUERADE
iptables -A FORWARD -i usb0 -o eth0 -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i eth0 -o usb0 -j ACCEPT

If you get any of the following error messages with iptables, you are probably missing one of the kernel modules mentioned above

iptables v1.4.21: can't initialize iptables table `nat': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.
iptables v1.4.21: can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.
iptables: No chain/target/match by that name.

If the NAT router is not the default gateway on downstream hosts, relaying packets to upstream networks may require you to setup routes. This can be done using commands such as

# On Mac OS X
sudo route -n add -net 10.0.0.0/8 192.168.0.101
# On Linux
route add -net 10.0.0.0/8 gw 192.168.10.1

Static route configuration may also be required in any downstream NAT routers.

Finally, a couple of useful commands to troubleshoot IP routing and forwarding

# List all rules in iptables
iptables -L -v
# A basic packet sniffer
tcpdump -A -i usb0
Posted in Linux, Raspberry Pi

Linux Network Connection Bridging


This time I add network connection bridging to my custom embedded Linux system for Raspberry Pi. That should allow me to experiment with bridging network connections for internet sharing, software testing, and so on.

Modify Linux kernel configuration

Execute the following in the buildroot folder to get Linux Kernel configuration menu

make linux-menuconfig

Select the 802.1d Ethernet Bridging module shown in the following screenshot

Ethernet Bridging

Modify Buildroot configuration

Execute the following in the buildroot folder to get the configuration menu

make menuconfig

Select the bridge-utils package, shown in the screenshot below. This package contains the brctl utility required to configure bridging.

bridge-utils

Then, just execute make to build the system. Once that is done, copy the new kernel image and root file system over to the SD card.

Perform bridging

These are the sequence of commands I typically use to bring up the bridge manually. I use a regular ethernet interface and a USB CDC ethernet interface for testing.

ifconfig eth0 0.0.0.0 promisc up
ifconfig usb0 0.0.0.0 promisc up
brctl addbr br0
brctl addif br0 eth0 usb0
ifconfig br0 up

If you need the bridge interface to have an IP address, you can assign one manually, or by invoking the DHCP client daemon as shown below. This is useful if you need to have access to your Pi over the network.

dhcpcd br0

To wrap it up, here’s how you can tear everything down.

ifconfig eth0 down
ifconfig usb0 down
ifconfig br0 down
brctl delbr br0
Posted in Linux, Raspberry Pi
Follow

Get every new post delivered to your Inbox.

Join 65 other followers

%d bloggers like this: