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Archive for April, 2010

XMega Solution for Kubuntu

29 April 2010 5 comments

Howdy folks.  For any penguin heads out there trying to get an XMega development setup for Linux, I finally got it working, and didn’t even have to compile anything!

My setup is a SparkFun XMega breakout board ($25) and an AVRISP mkII programmer, which I bought from Mouser (~$35) specifically for the new PDI programming.  Seems Atmel ditched the venerable ICSP programming method with these new chips.  The AVRISP mkII can program over the new “Programming and Debugging Interface”, but can’t debug.  If you want to be able to debug over the PDI interface, go for the JTAGICE mkII or another programmer.

I’m running Kubuntu Linux 9.10.  This solution probably won’t be all that useful for that long, because I imagine (but haven’t checked so I don’t know for sure) that Kubuntu 10.04 will have these updated packages.  Regardless, some of the advice that follows will still be pertinent to some people.

So here’s what I’m going to do: Set up my Kubuntu 9.10 installation to be able to compile for XMegas using AVR-GCC, program XMegas using AVRDude, and use Eclipse as an IDE for all this.

Install AVR-GCC and AVRDude

Since the packages in the Kubuntu 9.10 repository aren’t up to date enough to work with the XMega, we’ve got to get them from somewhere else.  I default to the Debian repositories, which 9/10 times work with Kubuntu.  I’m not sure if there are other packages you need installed, because I started with a working standard AVR and GCC development environment already working.  If installing these packages complains about dependencies (beyond those in the list below), using “apt-get” to install them from the normal repository should be fine.

Download the following “squeeze” packages for your system from here:

NOTE: Just install these from the repository using apt-get if using Kubuntu version 10.04.

There’s a specific order you have to install these in – I can’t remember exactly what it is.  Right click on the files in Dolphin (or, as I prefer to use, Konqueror) and use the GDebi package installer to install these files graphically, or dpkg to install from the command line.  Once these are installed, you can compile and program your XMegas from the command line!

Install Eclipse and AVR Plugins

Eclipse has some features that I’ve heard are pretty nice.  Traditionally, I’ve used and really liked KATE (KDE Advanced Text Editor), and recently I’ve gotten hooked on VIM, but I’m not a bigot about things I haven’t tried.  So here’s me trying Eclipse for AVR programming.

First stop, install Eclipse.  You’ll want Eclipse CDT, which is geared towards C/C++ development instead of Java.  You can download it here.  Install it by extracting it, pretty much anywhere.  I installed it into my development tools folder – another standard place is the opt folder (/opt/eclipse).  Further instructions on this can be found on this UbuntuForums post.

Once Eclipse is installed, you’ll want to add the AVR plugin.  Follow these instructions.

Start a New AVR Project

To start a new AVR project for an XMega, follow these steps:

  1. Click “File -> New -> C Project”
  2. Enter a new project name, and under the “AVR Cross Target Application” select “Empty Project”.  AVR-GCC Toolchain should be selected on the right side.  Click “Next”.
  3. Click “Advanced settings…”
  4. Click the “AVR->AVRDude” option on the left.
    1. Under the “Programmer” tab, select your programmer.  If it’s not in the list, or the list is empty, click “New…” and select your programmer.  For me, it was “Atmel AVR ISP mkII”.  Click “OK”.
    2. The rest of the options under the tab should be left with defaults.
  5. Click the “AVR->Target Hardware” option in the left pane.
    1. Select your processor.  For me, the “ATXMega128A1”.
    2. Select the frequency your processor will run at.  For me, 32MHz.
  6. Click “C/C++ General->Indexer”, then click the link on the top right titled “Configure Workspace Settings”
    1. Check the “Index unused headers” option.
    2. Check the “Index source files not included in the build”.
    3. Check the “Allow heuristic resolution” option, then “OK”.
  7. Click “Next”.
  8. Select your MCU type and frequency (again, I know…)
  9. Click “Finish” to create the project!

Setup Auto Programming

I think there’s another way to make this happen, but I couldn’t figure out how to make it program the chip.  So I did the following as well:

  1. Click “Run->Run Configurations…”.
  2. In the “Name:” box, type “Program Chip”.
  3. In the “C/C++ Application:” box, type “/usr/bin/avrdude”.  Make sure the “Connect process input & output to a terminal” is checked.
  4. Under the “Arguments” tab, type the following: “-c avrispmkii -p x128a1 -P usb -e -U flash:w:Debug/<project-name>.hex”
  5. Click “OK”.

Now at this point clicking the “Run” button on the toolbar (or its shortcut, Ctrl-F11) will program the chip.  We’re not out of the woods yet, though.  By default, a program needs root privileges to access USB devices.  So when you hit Run, it will ask you to enter your password (which will, stupidly, appear in plain text).  To make the AVR-ISP mkII programmer available to mere mortal (non-root) users, do the following:

1.  Open a terminal.  Start a text editor as root to create the file “/etc/udev/rules.d/50-usbavrispmkII.rules”.  For example:

> sudo kate /etc/udev/rules.d/50-usbavrispmkII.rules

2.  Paste the following into the editor:

SYBSYSTEM=="usb", SYSFS{idVendor}=="03eb", SYSFS{idProduct}=="2104", GROUP="users", MODE="0666"

3.  Run the following command in the terminal:

> sudo udevadm control --reload-rules

Now there’s no need to enter the password!  To recap, to build without programming hit “Ctrl-B”.  To build and program, hit “Ctrl-F11”.

That’s about all I can think of for settings I use, but if I think of anything else I’ll update the post.

An update to the post:

I found a little item I forgot.  In order for Eclipse to output a hex file (needed for the above instructions to work), you need to go to the project properties -> Settings, then check “Generate HEX file for Flash memory”.  Hit the build button again, and behold the appearance of a hex file.

Conclusion

A very nice feature Eclipse has is that it hyperlinks variables,  functions, and defines when you hold the Ctrl button and click.  For files within your project, it works pretty nice, but usually you already know most of those well because you wrote them.  Step 6 above allows the  indexer to look through the AVR include folder as well.  This makes any standard definition of a port, register, enum, or struct (of which there are many) easy to find.

Also, you don’t have to manage your makefiles.  Eclipse will take care of all that for you, so you just have to worry about programming.  One thing I haven’t figured out yet is how to get it to get the equivalent of  “make clean && make all && make program” happen, which I typically use when doing AVR programming.  I periodically have to use the “Clean…” menu option when things start acting strange.

As a side, make sure to check out the XMega app notes on the Atmel website, and download both the PDF and the source code.  I’ve found myself primarily using their drivers, which has really sped up getting started with this chip (even though the drivers do have their limitations).

Happy programming!  I imagine this post will be the cause of a lot of late night hacking and Mtn Dew sales …

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Hacking Tiny Servos

Thought I would blog about hacking the 9g servos from SparkFun and converting them to continuous rotation since I’m performing said hack for an upcoming project.  I’m sure there are more and better instructions on how to do this, but I’ve looked at tutorials before for larger servos and noticed these little guys are a bit different.

What I’m doing is changing a servo that normally has around 90-120 degrees of motion to have full 360 continuous rotation.  Instead of the servo reacting to the standard PWM signal as a position signal, it will now act as a velocity signal with full forward/stop/reverse control!  Best of all, when people tell you the servos on your YT-1300 look like a piece of junk, you can tell them you’ve made a few special modifications yourself.

Apology in advance for the images – I promise to never use my cell phone cam for blogging again!  It’s abysmally unfit for close up pictures of electronics.


Take the servo apart

The black circular piece with the shaft in it, next to the gears, is the potentiometer. Two stops are there, two more are on the case piece to the left of it.

Remove the sticky label (goo-be-gone is needed) and remove the screws.  You’ll likely need a jewelry screw driver.  Pull all three sections apart, remove the gears, and remove the white plastic cover over the potentiometer.  Easy peasy.

Cut out the stops

I’m running on memory, so feel free to correct me in comments if I’m wrong.  I recall this as the part that’s different from the standard sized servos.  There are stops on the potentiometer and you practically have to cut out half of the pot to get it to rotate properly.  This is because the pot shaft is used as the axis for the gears and external drive shaft.  Boo to the man that designed it this way, unless it made it significantly cheaper.  In that case, yay… but boo.

Warning: The plastic on the pot is EXTREMELY brittle.  If the pot case crumbles, your servo is trashed.

Proceeding onward.  You’ll see two plastic stops in the pot – cut it out in small pieces.  Once that’s gone, you’ve got to remove the potwiper.  The copper-colored middle terminal of the pot should come out with a little force at this point.  There are a couple of “C” shaped metal tabs that will come out with it.  Now cut the entire terminal off and leave the wire hanging for now.

On one of my servos, I cut it out without pulling the shaft out.  On another, the shaft hole cracked cand the whole shaft came out which made this easier – but I’ll have to report later as to whether it still works well or not.

You also need to cut out the springy piece.  You can’t remove it completely, it appears to be connected with the shaft itself, so you’ll need to cut it flush against the remaining metal flange.

The final stop that has to be cut is on the actual case, just inside the hole where the shaft exits the case.  Flush cutters make quick work of this, but an Xacto knife could probably work too.

Solder resistors in place of pot

With the middle terminal removed and cut off, solder resistors between the two terminals and then solder the middle terminal wire to the middle of the resistors.

So that the potentiometer has a reference point for its control loop, we need to solder resistors in place of the pot.  I used two 10K resistors, which will make the signal that would have centered the servo be the stop position.  Positions signals right from the signal will be forward, and positions left from the signal will be reverse.

Solder the two 10K resistors (surface mount or 1/8W or smaller should fit) in series between the two remaining posts.  Then solder the currently-floating middle terminal wire in between the two resistors.

Put the servo back together

Pretty straightforward.  Do step one in reverse.  The gears may feel like a puzzle, but there’s only one way they fit.  Lastly, be careful with the screws – they strip out pretty easy.


Shazaam!  Full control of a motor with great torque/gear ratio with only a half hour’s worth of effort.

Catch up…

13 April 2010 3 comments

Looks like it’s been a while since I’ve posted, but not to fear – my projects never cease.  In fact, they seem to spread faster than lice on Kashyyyk.  Here’s what I’m up to right now, and what’s coming up for those of you who have been following the ZephyrEye project.

First, here’s what I “have” to be working on right now.  I’ve enrolled in the ME414 “Mechatronics” class here at OSU, where interdisciplinary groups of three CS, ECE, and ME students have to put together a checker playing robot.  Seriously!  It has to autonomously play checkers not only against humans, but other robots.  At the expense of my other relatively boring classes, this one gets most of my spare time.  I’ll keep you posted on how it’s coming, as there’s some overlap with other projects – in particular, I’ll be using the XMega controller on this project and I’ll be posting some tips on how to get started (as I’m figuring it out, no less ;).

Back to the ZephyrEye.  I’m currently working on the project with a kit manufacturer and we’re making good progress.  No promises of any kind, but I’m currently estimating they will be on shelves by this summer.  Oh, the heaps of gold I could have made if only I hadn’t open sourced this project ;).  Can’t wait to start coding this sucker up, make sure and sign up for the Google Code project if you’re interested in helping out!

Hopefully my summer schedule lets me work on the project!  It’s getting full.  I’ve landed an exciting internship at the Robotics Institute of Carnegie Mellon University, so I’ll be racking up frequent flier miles going cross-country to Pittsburgh.  Exciting stuff, I get to work with and get to know some crazy smart people who design bleeding edge robots.  I’ll be looking for the secret to the universe in the bookshelves, for sure …

And, the missus and I are expecting baby #2 in September.  Yay!

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