Setting Up PWM for BeagleBone Black

BeagleBone Black Pin-modes

As can be seen on the BBB, it has a number of usable pins at your disposal. Through further inspection I found out that one pin can have up to seven different modes. For instance one pin can be used for regular GPIO, PWM, UART, or I2c; this is done by pin-muxing. So through multiplexing the different modes can be set. Because the BBB does not POST at boot the only way to initialize hardware capabilities is through Device Tree Overlays (DTO).  A DTO can be considered the equivalent of a driver. I am not sure if this is correct, but I am just stating what I have gathered from it through my own research. The best resource I have found with working with the BBB is on Derek Molloys site. I wouldn't have been able to get as far as I have in such a short time with watching his videos. A link will be posted I really recommend going there for more cool things BBB.

Setting up PWM 

To activate the pins the device tree overlays must be added to:

                    /sys/devices/bone_capemgr.8/slots

To see what pins can be used go to:

                   /lib/firmware

For most applications it would be nice to keep from having to do this manually every time you turn your BBB on. To do this, change the uEnv.txt file inside /media/BEAGLEBONE. An example of what I added to it to run three PWM pins can be seen in Figure 1. Additionally, If you are using a pin that by default is set for HDMI out, you will have to mount the file path manually. Both steps will be in Figure 1.

Figure 1: Mounting filepath, and changing file

 To make it easier to access my Pins and Slots I made multiple shortcuts by modifying the .profile inside the /etc directory. I did this by exporting the file path into a user defined name, see Figure 2.

Figure 2: Adding shortcuts in .Profile

With these modifications everything should be set at boot-up. To check the pins you can set the period and duty cycle to the shortcuts by echoing a value for each. Every servo is a little different, so the values can change. In the first video I show setting the period and duty cycle. The values will be close so they are a good reference.

Resources:

Derek Molloys BeagleBone Black site

 

Setting up for Cross-Compilation with Eclipse (CDT)

In order to program the BBB cross-compilation is necessary. Because the system I will be using to program the board is x86 architecture and the BBB is using ARM architecutre. So I will be setting Eclipse to do this and will show the entire process that I used in order accomplish this task. I am running Ubuntu 12.04 LTS on my personal desktop to do this (not a virtual system).

Installing Eclipse (CDT)

Figure 1: Installing Eclipse

Before you can set it up you need to install it first, if you have not already. So I opened a terminal and installed Eclipse along with C/C++ development tools, and the compilers for C/C++. As can be seen in Figure 1 I already had it installed on my system. To install it though the terminal enter:      

sudo apt-get install eclipse eclipse-cdt      
sudo apt-get install g++ gcc


After doing that I had my best results by updating everything before I progressed any further.


Because we are compiling to a separate system I also needed to install these in Eclipse:

• Remote System Explorer End-User Runtime
• C/C++ Remote Launch

To install those I opened Eclipse and went to Help>>Install New Software. A window popped up like in Figure 2 below. I then clicked on the down arrow at the top of the page and selected Indigo Update Site. Remote System Explorer End-User Runtime is located under general purpose tools. C/C++ Remote Launch is located under Mobile and Device Development. 

Figure 2: Installing add-ons 

Making it ARM Ready

Next step I did was install the toolchain for the BBB. In the terminal I entered:

Figure 3: Checking it installed properly

sudo apt-get install gcc-arm-linux-gnueabi

sudo apt-get install g++-arm-linux-gnueabi

It takes a minute or to, but afterwards if you type arm-linux and press tab a couple times you should end up with something similar to what is shown in Figure 3.

Figure 4: Hello World

At this point a C++ project can be made in Eclipse. For first time set-up I just chose the Hello World C++ Project, that way I can test it right away, Figure 4. By clicking on the hammer to build it and the green button with a white arrow(Run) on it it should display "Hello World". To send it to the BBB you have to change the build settings. By right clicking on your project you can go to properties>>C/C++ Build>>Settings. Going back to Figure 3 I had to input the proper commands for each. Figure 5 shows all four changes that I made.  

Figure 5: Changing Build Settings

Setting up Remote Application

To send the program to run on the BBB, go to run configurations under the run button. Double click on C/C++ Remote Application and create a new connection. The remote system type is Linux, the host name should be the ip address of your BBB. The address from the USB host would be 192.168.7.2. It will change if you are using the Ethernet port  and do not have a static IP setup. I have been using a static ip but will show how for the USB because I do not have it as a connection type in Eclipse. Follow the Figures on how to configure the connection.

Figure 6: Making new connection

The last part is to give it a file path. Figure 6 shows an example of how that can be done. The part marked by a blue box is what the name of the program will be inside your BBB. The red boxes are what I changed. Click run and it should send it to the BBB. It will automatically run it as soon as you send it. You can also call it from the BBB by typing ./ProgramName while ssh-ing to the BBB.

Figure 11: File Path

Resources:

cross-compile-for-beaglebone-black by Michael H Leonard

What is a BeagleBone Black?

The BeagleBone Black (BBB) is an ARM community-supported development platform for developers and hobbyists. It comes pre-installed with Angstrom Linux but it is compatible with other operating systems like Ubuntu, and Android. While it can be used as a desktop computer its main advantage compared to similar boards is all the pins that are available to the user.

Specifications:

• AM335x 1GHz ARM Cortex-A8
• 512MB DDR3 RAM
• 2GB 8-bit eMMC
• 3D graphics accelerator
• NEON floating-point accelerator
• 2x PRU 32-bit microcontrollers
• USB client for power and communications
• USB host
• Ethernet
• HDMI (1280x1024)
• 2x 46 pin headers

 
That is just a little bit of information on the Beaglebone Black, check out the link below if you wish for more.

Beagleboards website


Project Description:

Using the BeagleBones pulse width modulation (PWM) an analog-to-digital converter (ADC) pins I plan to make an autonomous robot. I have done something similar with an Arduino before, but wanted to branch off from that to something more powerful. Being that I have never done anything with it before I decided to keep it as simple as possible using two continuous servos for the wheels and a standard servo to look with an infrared (IR) distance sensor.