Dedicated SBC Camera Monitor

A guide to setup an SBC (beaglebone black) or Desktop that will monitor a video feed from ZM. Simply press the power button, and the video feed will appear on boot.

OS will be Devuan Jessie, WM will be dwm, terminal st, and browser will be surf. It will be a minimal installation. Leaner than LXDE, the default DE for beaglebone.

I'll include optional steps to setup the I2C peripheral (BBB) and read a sensor. Combine with ZMTrigger.

This is noticeably more difficult than connecting a coaxial cable to a CRT such that an analog, older setup would have.

Setup

Installation

Requirements

• At least 4GB SD
• SBC / Desktop / Laptop
• Internet connection
• Computer monitor
• HDMI cable for BBB (I use a HDMI to DVI adaptor)
• Novice to Intermediate GNU/Linux experience

Install Beaglebone Black Debian Jessie using elinux.com's BeagleBoardDebian page.

Use the direct image (under Demo, below NetInstall). Not the netinstall, which is slower, unless you know what you are doing.

After booting from the SD card, make sure the network interface is set to load in:

nano /etc/network/interfaces

Next, migrate to Devuan using Dev1fanboy Upgrade-Install-Devuan wiki guide. Skip most of the part about the display environment. Reboot after apt-get dist-upgrade. Try the purge of libsystemd0 in DE section, if you like. May not work. RCN repo seems to want it.

Complete the following commands

 sudo su

 apt-get install xorg libx11-dev libxft-dev libxinerama-dev gcc make htop sudo tcpdump

For Surf

 apt-get install libwebkitgtk-dev libgtk2.0-dev linux-headers-$(uname -r)

Download simple programs

 git clone http://git.suckless.org/dwm && git clone git://git.suckless.org/st && git clone git://git.suckless.org/surf

Edit the config for dwm

 nano dwm/config.def.h

• Later Disable the bar
• Later Remove all workspaces except for 1 (*tags)
• Set Mod4Mask as modkey (redmond key)
• Set MODKEY|Shiftmask to 0 and XK_c to XK_F12 for killclient (personal preference)
• Later disable spawm of dmenucmd and termcmd, but for now leave enabled.

cd dwm
make
make install
cd ../st
nano config.def.h

• Set termname[] to xterm (resolves some issues with programs that don't understand default termname).

make
make install
cd ../surf
nano config.def.h

• Review options
• Later set runinfullscreen to TRUE
• Later set kioskmode to TRUE once debugging is over

make
make install

Cleanup

apt-get remove nfs-common rpcbind wpasupplicant avahi-daemon ofono apache2

Leave wpasupplicant if you use wifi. Net installer may want to install acpid. Beware of removing cron. Just disable the service. Remove Exim4 if you want.

At this point maybe 40MB RAM, and <5% CPU. Compare to LXDE.

Clock

Only needed if you are keeping time.

# apt-get install ntpdate

Set cron to run ntpdate periodically

*/5 * * * * ntpdate pool.ntp.org

This is leaner than running ntpd 24/7

Auto Start

Edit .xinitrc, /etc/rc.local, /etc/inittab, and .bash_profile to auto startx without requiring a login, load surf with the path of the zm server monitor feed, and disable the screensaver.

Added to /etc/inittab (replace existing):

1:2345:respawn:/bin/login -f USERNAME tty1 </dev/tty1 >/dev/tty1 2>&1

Copy /etc/profile to user that will be auto logging in:

cp /etc/profile ~/.bash_profile

Appended to ~/.bash_profile for USERNAME:

exec startx

When startx loads, it will pull settings from ~/.xinitrc for USERNAME so edit that (note that .xinitrc requires & after all commands that are not the final wm).

#!/bin/bash
/usr/local/bin/surf "localhost/zm/cgi-bin/nph-zms??mode=jpeg&monitor=1&scale=100&maxfps=5&buffer=1000&user=user&pass=pass" &
exec dwm

Add another user beside the one used for the auto login, otherwise ssh will fail. ssh will try to startx when it loads, and it won't be able to. Add USERNAME2 permissions to sudoers.

# adduser USERNAME2
nano /etc/sudoers

Disable screensaver per Arch Wiki: Display Power Management SIgnaling

nano ~/.xinitrc

export DISPLAY=:0 &
xset s off &
xset -dpms &

These go before the other commands in .xinitrc, as they have the & symbol.

Note: When troubleshooting xset. You must be the same user that is running X (ssh in as different user, then su to user). And, you must export DISPLAY to :0 or similar. Finally xset q should query the current settings.

Fine Tuning

At this point, you should be able to boot the SBC or desktop and receive a video feed without user interaction. However there are two problems. One, it is not full screen. Two, video may be flickering.

Flickering Video

This is a known issue with Beaglebone. The simple solution is: install devmem2 or some other memory editing program, change an address. For details of why this is occuring see: [1] and [2] or search online.

Steps:

git clone https://github.com/VCTLabs/devmem2
cd devmem2
make
make install

Append the memory adjustment to rc.local

nano /etc/rc.local
devmem2 0x4c000054 w 0x00FFFFF10

Watch syslog and FIFO errors should immediately stop upon entering write command on memory.

Install steps source: Scivision: Devmem2 on the beaglebone black The author of devmem2 (Jan-Derk Bakker, website and code found at lartmaker.nl), his website is down at the moment. You can view the root domain at internet archive, but the page for devmem2 is not available. Others like VCTLabs above have copied his code to various spots.

Full Screen Video Feed

Two options come to mind:

• Point browser to a local html page with the link to the monitor embedded in an img tag

OR

• have a local web server run and point surf to a hosted html page.

First Is easiest. Make an html file. Be sure to include http prefix.

<html>
<img width="###px" height=###px" src="http://serverip/zm/cgi-bin/nph-zms?mode=jpeg&monitor=####&scale=100&maxfps=5&user=username&pass=password" />
</html>

Call it on .xinitrc

surf file:///home/username/file.html

Customize the width and height of the img tag to fit your monitor. In my case I put st in the .xinitrc of my bbb instead of surf, restarted, and from the terminal ran xrandr to see what display it was using. I had 1440x900 but the width and height I could get out of surf without borders causing trouble was 1415 and 875. Multiple img tags can be embedded into an html file however you like.

This procedure has been tested 03/2017 on Devuan Jessie and a Beagle.

Using the Breakout Headers

Device Trees and Pin Initialization

Here are some notes, from my own setup of I2C on the BBB. It can be confusing if you are new to the BBB. This guide is helpful for configuring the peripherals or GPIO of the BBB.

https://github.com/beagleboard/bb.org-overlays

Follow this link. Ignore the part about pre built kernels if you used the RCN based installer or image from elinux.org's BeagleBoardDebian. You already have cape manager support.

If you don't have DTC where is asks for it in the 2nd step for dtc -version, ignore that step. The ./dtc_overlay.sh script will install the latest compatible device tree compiler.

Next

https://github.com/cdsteinkuehler/beaglebone-universal-io

And use this to configure the pins.

There are also preset modes with the pins configured in various states, but I found it more satisfying to customize them to my needs.

cd ..
git clone https://github.com/cdsteinkuehler/beaglebone-universal-io
cd beaglebone-universal-io

No installation is required for config-pin.

Test it now:

 ./config-pin overlay cape-universal

This will allow a lot of pins to be edited. This must be done first. Then you can configure pins. There are other modes as well, see github. Cape-universal exports all pins except for HDMI and EMMC pins.

#:~/beaglebone-universal-io# cat /sys/devices/platform/bone_capemgr/slots
 0: PF----  -1
 1: PF----  -1
 2: PF----  -1
 3: PF----  -1
 7: P-O-L-  0 Override Board Name, 00A0,Override Manuf, cape-universal

Now you can run something like this:

./config-pin p8_07 hi

To set Pin 07 on header 8 to GPIO HI

To see more options

./config-pin -h

e.g.

./config-pin -l 9_11
default gpio gpio_pu gpio_pd uart

Showing us we can set the pin to UART or one of the GPIO modes.

 ./config-pin -a 9_11 uart

Then we can access the UART through either the direct memory registers, or the linux file system access (search online for more details).

The config-pin overlay cape-universal can be set in /etc/rc.local as well as individual pin settings.

I2C Usage

 
# apt-get install i2c-tools

List

# i2cdetect -l

The i2c peripheral, after being connected to the BBB, will be on one of the three i2c buses. Either 0,1, or 2.

# i2cdetect -r 0

Here we search on 0.

I used a BMP180 barometer and mine showed up at 77.

Unfortunately, the sensor can't be read from without a driver. What you will need to do is recompile the kernel with that driver included, as linux has a driver for the BMP085, but not by default.

References: (from http://elinux.org/EBC_Exercise_12_I2C) [3] [4]

Recompile Kernel With Sensor Driver

I tried building the kernel natively on the Beagle, but this failed. It is best to cross compile from a Debian based distro. I received an error trying to cross compile on Gentoo.

http://elinux.org/EBC_Installing_Kernel_Source is a good guide that doesn't require javascript (as RCN's docs do).

Finally, with the kernel built with support for your i2c device, (in this case a barometer):

su root
echo bmp085 0x77 > /sys/class/i2c-adaptor/i2c-1/new_device

Again, these steps are only valid for the bmp085, and when it's on i2c-1. Review dmesg

$ dmesg -T

Finally for the BMP085, you can navigate to /sys/bus/i2c/drivers/bmp085/1-0077/ and review what the file system provides access to from the BMP driver to interface with the sensor.

References: [5] [6]

Troubleshooting

Installing and updating programs takes too long!

While these SBCs are slower than a desktop, it is also possible you have a counterfeit SD card that is slowing down all installs. A counterfeit or non name brand SD may take one day, what takes 2 hours to do with a name brand card.

Video feed flickers, syslog says FIFO underflow!

See install steps regarding adjusting memory addresses with devmem2.

How do I disable keypresses, or whatnot for a real kiosk mode?

Look online. I don't have the need, so I have omitted it, but it's possible to do further lockdown.