BeagleBone for Secret Agents

BBB has another very important quality: it is Open Source Hardware (OSHW). OSHW is a relatively new concept, the exact definition of which may confuse people. However, there is a group, the OSHW Association (OSHWA), whose mission is to educate and promote OSHW. Their definition is maintained on their website: http://www.oshwa.org/definition/. As with most organizations, a consensus for a definition can be difficult to obtain. The definition of OSHW is well over a page. The complication with defining OSHW from open source software is that hardware is a physical thing. There are design files to manufacture hardware, but there are physical components also. To make a software analogy, the compiler for the hardware is the manufacturer. Therefore, the definition of OSHW is carefully constructed and it generally applies to the design files of the hardware.

BBB is OSHW, in that it releases documentation, schematics, Computer-Aided Design (CAD) files, Bill Of Materials (BOM), and production files (Gerbers), all under a Creative Commons license. This means that you can not only study the complete design but you are also free to make your own derivative BBB.

Unlike Raspberry Pi, BBB is ready out of the box. A recent BBB will come with the Debian distribution of GNU/Linux, henceforth referred to as Debian, installed on the eMMC. eMMC is the on-board flash memory for the BBB. As soon as power is applied to the board, BBB will start to boot from the eMMC. As shown in section three of the SRM, you can connect the BBB directly to your PC with the supplied USB cable. The BBB can also be powered from a 5V barrel jack, where you'll want a wall adapter that can supply up to 1A. If you plan on connecting a mini liquid-crystal display (LCD) to the BBB, you may want to use a 2A adapter. You can typically find the output voltage and amperage specifications written on the adapter. You can tell whether the board is powered and running if the blue user light-emitting diodes (LEDs) are flashing. Specifically, the LED USER0 will flash in a heartbeat pattern.

The BBB can support multiple peripherals such as a keyboard, mouse, and monitor. However, in this book, we'll be using the BBB in a headless configuration, which means without the monitor. Section 3 of the SRM details the various connection scenarios.

The history of Emacs is about as long as the history of modern computing. As an editor, Emacs is often overlooked because of its reputation of being outdated and difficult to learn. Emacs can be overwhelming since the interface is different from most modern interfaces. Also, the keybindings were created prior to the invention of modern Graphical User Interfaces (GUIs), so the keybindings don't correspond to the shortcuts that you are typically accustomed to. However, there is active development on various Emacs starter packs, which provide a smoother Emacs experience. If you keep in mind that Emacs predates your operating system, you may find it easier to accept the Emacs way.

Embedded development is slightly more complicated than web or desktop development because there are typically two machines involved: the host (your main computer) and the target (your embedded platform). Embedded systems range in capabilities and some run without an operating system, which certainly can't support running a compiler. In this case, the user cross-compiles the code on the host for the target. This can be performed for the BBB, but compiling small programs natively on the BBB does not take too long.

A common recommendation for development on the BBB is to connect to the device over Secure Shell (SSH) and to use command-line tools. This can be an effective technique, but this limits you to the command line and your terminal emulator. These tools are very powerful and in this context, limited does not mean limited in functionality but limited in the interface.

The one helpful feature of Emacs for embedded development is Transparent Remote Access Multiple Protocol or the TRAMP mode. In short, the TRAMP mode lets you run Emacs on your host machine, which is most likely more powerful than the BBB, but access files and run commands on the BBB as if they were local. This is transparent in TRAMP; working in this environment feels like you are working on a host, not on an embedded platform. The following screenshot shows the TRAMP feature of Emacs:

This screenshot was captured with Emacs running on Mac OS X, but connected to a BBB with the hostname slartibartfast. Everything on this screen is running on the BBB. In the top-left corner, the frame shows a live debugging session with the GNU debugger (GDB) on a simple C program. In the bottom-left corner, the frame shows the compilation result obtained from running gcc on the BBB. In the top-right corner, the frame shows the interactive gdb session. Lastly, in the bottom-right corner, the frames show the current directory and a shell, respectively. In the following sections, we'll provide details on how to install Emacs and set up this development environment.

We'll need Emacs 24.x to take advantage of the prelude starter pack by Bozhidar Batsov. Prelude is under active maintenance by Batsov and dedicated prelude users. The code is maintained on GitHub (https://github.com/bbatsov/prelude), where there is a detailed README. This software is optional; however, it adds many convenient features and reasonable default configuration settings. Installation procedures for Emacs vary greatly by operating system, but you can consult the following table for the software locations:

If you are a Windows user and are having trouble installing Emacs, consult the guide at https://www.gnu.org/software/emacs/manual/html_mono/efaq-w32.html. Mac users should find the binaries listed in the previous section sufficient. If you are using a *nix machine, you can either use your package manager to install Emacs or build from the source. If you use the package manager, be sure to install Emacs' major version 24. In a Debian-based system, the command is apt-get install emacs24.

The Emacs prelude software can be installed by typing the following command:

curl -L http://git.io/epre | sh

If you are wary of shortened URLs, take a look at the prelude README for alternate installation instructions, which is available at https://github.com/bbatsov/prelude. The installer will complain about any missing packages that you need to install. Once complete, you should run Emacs. If you have installed a binary version for your OS, double-clicking on the icon should suffice. On a command line, just type emacs to launch the program. On the initial start, Emacs will attempt to go to the Emacs package managers and download additional software. It will then byte-compile the source files, so it takes a minute or two. Once this is complete, close Emacs and open it again; you should see something similar to what is shown in the following screen:

Emacs has too many features. Here's a tongue-in-cheek joke: Emacs is an operating system that is in need of a good editor. This section will illustrate the basic skills that one needs to use Emacs and more importantly, to learn how to use Emacs. One of the best features of Emacs is the immense built-in help. If you have never run Emacs before, press Ctrl-h t, abbreviated C-h t. This means that while holding the Ctrl key, press h, then release it, and then press t. Also, note that the Emacs commands are case sensitive. C-H T means to press Ctrl + Shift + H, then hit Shift + T, whereas C-h t is performed without the shift modifier. You'll be presented with the interactive Emacs tutorial. This tutorial will teach you the fundamentals of Emacs. In the tutorial, you'll see references to a meta key, which you will be hard pressed to find on your keyboard. Command sequences, such as M-x, mean to hold down the meta key while pressing x. Depending on your system, the meta key may be Alt or Option. If neither of these work, you can press the Esc key and release it to provide meta.

The tutorial is very good and for the rest of this chapter, it is assumed that you have completed this tutorial or have an equivalent level of knowledge to understand the more advanced features.

Even if you don't use Emacs, you'll find yourself frequently connecting to the BBB with SSH. If you run the BBB from the USB cable attached to your PC, then the default Internet Protocol (IP) address of the BBB will be 192.168.7.2. However, if you want to download software directly to the BBB, as you will need to do in order to complete these projects, you'll have to forward your Internet connection from the PC to the BBB. Also, when powered from the USB directly, there is typically a 500mA current limit. When the BBB is powering expansion boards or other peripherals, it'll need to be powered from a 5V DC plug that can supply up to 1A. As a result of these two issues, you may find it much more convenient to run the BBB from a 5V power supply and connect the Ethernet cable into your home network directly.

When you do this, the IP address will most likely be assigned by your router and will only be known to your router. This will leaving you staring at the BBB pontificating over its IP address.

Discovering the IP address of your networked BBB

There are a few ways to discover the IP address of your device. The first way is to log in to your router and look up the IP address. This is a quick method but as there are numerous routers, you'll have to consult your router's documentation on how to accomplish this.

You can also use the nmap utility to conduct a quick ping scan on your network. Assuming that you are familiar with the IP address of your own network, you should be able to see a new device. If you are running an apt-based distribution, you can install nmap with sudo apt-get install nmap. If you are on a Mac, you can use the homebrew package manager (http://brew.sh/) and install it with brew install nmap. Windows users should download the binary from http://nmap.org/download.html#windows. Once it is installed, you'll want to run a command similar to the following:

nmap -sn 192.168.1.0/24

Replace 192.168.1.0 with the appropriate address for your network. /24 is the Classless Inter-Domain Routing (CIDR) notation for the subnet mask. In this case, /24 means use a subnet mask of 24 bits of 1's, or 255.255.255.0. The -sn option directs nmap to conduct a ping scan.

If you are still unable to determine the IP address, you can buy a USB-to-serial adapter cable. BBB has a serial debug header located inboard of the P9 header. You can attach the USB-to-serial adapter to BBB's serial debug header, as shown in the following image:

In this figure, pin 1 (which is the black wire) is the ground, pin 4 is receive, and pin 5 is transmit. Once physically attached, you'll need a terminal emulator to connect over the serial connection. GNU Screen is a widely available, free, and robust software that will connect with the following command; just replace /dev/tty.XXXX with the file of your connection:

screen /dev/tty.PL2303-004014FA 115200

Lastly, you can set a static IP for your BBB. Your router may support a static lease feature, which will assign the IP of your choosing to the device when it performs a Dynamic Host Configuration Protocol (DHCP) request. The lease on this request can be indefinite and, therefore, effectively provides a static IP. You can also set the IP statically on your device, but then you will have to manage conflicts manually. Therefore, the preferred method is to let the router handle this situation.

Tip

To find a serial debugging cable, see the eLinux page at http://elinux.org/Beagleboard:BeagleBone_Black_Serial.

To take full advantage of the SSH configuration options in the following section, you'll want to have a static IP set. Otherwise, you will have to repeat the previous steps to determine the IP address of the device when your router power cycles or if the BBB is disconnected for a few days.

Tip

If you prefer to use a WiFi connection instead of Ethernet, be aware that there are issues with some dongles. Refer to this eLinux page for supported adapters: http://elinux.org/Beagleboard:BeagleBoneBlack#WIFI_Adapters.

ssh debian@192.168.1.10

ssh-keygen -t rsa -b 4096

Host bbb
     HostName 192.168.1.10
     User debian

rm /etc/ssh/ssh_host_*
dpkg-reconfigure openssh-server

ssh-keygen -R bbb

cat .ssh/id_rsa.pub | ssh bbb 'cat >> .ssh/authorized_keys'

ssh_upload(){
  if [[ $# -ne 1 ]]; then
    echo "usage: host\nNOTE: host should be set in ~/.ssh/config"
    else
    cat ~/.ssh/id_rsa.pub | ssh $1 'cat >> ~/.ssh/authorized_keys'
    fi
}

ssh_upload bbb

source ~/.bashrc

Now that we've configured SSH, we will now have an easier time connecting to BBB with TRAMP and Emacs. Emacs has a built-in directory editor called dired, which can be invoked by pressing C-x d. We want to open dired on the BBB to view the remote files. Press C-x d and then enter the following for the directory: /ssh:bbb:/home/debian. A screen similar to the following should immediately open, which will show you the contents of the home directory:

All the basic Emacs navigation commands work in dired, so you can navigate the directory and press enter to open a file or another directory. The ^ key will navigate you to the parent directory. You can also click on the directories or files to open them.

For more information on dired or anything about Emacs, you can view the built-in documentation by pressing C-h r. If you scroll or search (by pressing C-s), you'll find the dired manual on that page. The manual uses the info viewer, and you can read about this by pressing C-h i to get the main information page and then pressing h.

One of the features of Emacs is its extensibility. Presumably, you will be connecting to the BBB often, pressing C-x d, and typing /ssh:bbb:/home/debian can be tiresome. Let's define a new key sequence to make this easier. Switch to the scratch buffer in Emacs. This can be done by pressing C-x b, then typing *scratch, and then hitting Tab + Enter. Paste the following code:

(global-set-key
 [(control x) (control y)]
 (lambda ()
   "Open a dired buffer on the BBB"
   (interactive)
   (dired "/ssh:bbb:/home/debian")))

Position the point, what Emacs calls the cursor, after the last parenthesis. Then, press C-x C-e to evaluate this snippet of Emacs Lisp. The mini buffer should echo the result. Now press C-x C-y and you should see the home directory of BBB. Congratulations! You've just customized Emacs! If you restart Emacs, however, you'll lose this convenient function, so you need to save it. If you are using the Emacs prelude, customizations should go in ~/.emacs.d/personal/foo.el. You can save this buffer with C-x C-s and specify the filename.

If you enjoy using Emacs, you will probably enjoy changing Emacs, which can be done with Emacs Lisp. Of course, Emacs contains a great manual to learn Emacs Lisp, An Introduction to Programming in Emacs Lisp. It can be accessed by pressing C-h i d and then you can either scroll down to the manual or press m, type Emacs Lisp, and then press Tab for tabcompletion to Emacs Lisp Intro.

The projects in this book all use some sort of cryptography. If you are familiar with terms such as asymmetric cryptography, digital signatures, and message authentication codes, then you should be OK. If not, you will still be able to complete the projects but you may not appreciate the theory behind them.

As this is not a book on cryptography, a primer here will not provide enough detail for a beginner and will be woefully inadequate for someone familiar with the material. If cryptography is new to you, you can still proceed with the book. In the beginning of each chapter, there is some tailored background to explain the material, which should be enough for you to understand what the project is trying to accomplish. Once complete, hopefully, you'll be interested in cryptography and you can get more information from the following resources.

For a gentle introduction to the topic, Cryptography: A Very Short Introduction by Fred Piper and Sean Murphy, Oxford University Press, 2002, is good starting point. However, as the title suggests, it lacks technical depth. Understanding Cryptography: A Textbook for Students and Practitioners by Christof Paar et. al., Springer, 2010, is a more detailed introduction. For the more inquisitive readers, Introduction to Modern Cryptography by Jonathan Katz and Yehuda Lindell, Chapman and Hall/CRC, 2007, is a good up-to-date reference.

If lectures better suit you, you are in luck. Khan Academy has some interesting and free mini-lectures covering ancient cryptography up to RSA (https://www.khanacademy.org/computing/computer-science/cryptography). Another free resource is Coursera, which has three cryptography classes, Cryptography I and II taught by Standford Professor Dan Boneh, and a Cryptography class on modern cryptography taught by Jonathan Katz. The links for these classes are https://www.coursera.org/course/crypto, https://www.coursera.org/course/crypto2, and https://www.coursera.org/course/cryptography, respectively.

Similarly, this book assumes some basic electronics knowledge. If you are looking for a book, Practical Electronics for Inventors, Third Edition by Paul Scherz and Simon Monk, Tab Books, 2013, is a solid and approachable reference. Khan Academy has a series on basic concepts in electricity and magnetism as well (https://www.khanacademy.org/science/physics/electricity-and-magnetism). Dave Jones EEVBlog is an entertaining and informative video blog that covers many areas of electronics and should be of interest to hobbyists in electronics (http://www.eevblog.com/).

For those new to Debian, there is an comprehensive and free handbook available online called The Debian Administrator's Handbook by Raphaël Hertzog and Roland Mas, Freexian SARL, 2014, at http://debian-handbook.info/browse/stable/. At a minimum, you should read Chapter 6, Maintenance and Updates: The APT Tools, of this book, which details how to use the apt set of tools for package management. There is also a free class offered by the Linux Foundation and edX called Introduction to Linux (https://www.edx.org/course/linuxfoundationx/linuxfoundationx-lfs101x-introduction-1621). The class is fairly recent and it does not appear to use the Debian distribution, but it does seem like a representative course on generic Linux information. Lastly, there are several Debian IRC channels on the OFTC IRC network. Most of the channels start with #debian and you should be able to ask specific questions there. The BeagleBoard channel is #beagle on Freenode, and there will be people there who can help answer your questions as well.