Saturday, April 16, 2011

Smoked my first ATMega328

I have been having a lot of fun upgrading my toolset for building AVR applications and hardware solutions.  I have been playing around with both the raw WinAVR toolset as well as AVR Studio from Atmel.  I also recently obtained a JTAGICE mkII from Atmel to hopefully be able to do some realtime debugging on my projects rather than having to always put serial port print statements in for debugging purposes.

The ATMega328 does not have a JTAG interface but instead has a one-wire On Chip Debug interface called debugWire. I do all my programming of the chip using an ISP (In System Programming) interface.

The Atmel device implements the notion of "fuses" that are basically switches that control certain feature or modes of the device.  One of these fuses (DWEN - debug wire enable) is used to enable/disable debug wire mode.  The debugWire pin is shared with the reset pin, so automatic reset hardware has to be disconnected for debugWire to work, which according to the Arduino Uno schematic is a non-issue.

So, for debugging you start in ISP mode to set the DWEN fuse. Unlike JTAG chips which have the JTAGEN fuse enabled by default the debugWire chips have DWEN disabled by default.

Once you have used ISP to switch to debugWire mode in theory you only need two of the 6 wires in the ISP header but as you need all 6 to get the chip back from debugWire to ISP mode (you can't change fuses in debugWire mode) you might as well leave all 6 connected. While in debugWire mode, the ISP mode is completely disabled.

So, since Murphy is still on the payroll of course, my first debugging experience ended up putting my ATMega328 in a mode where it can no longer debug, but the ISP interface is disabled so I can do nothing with it.

One possibility is that I have messed up the system clock fuses somehow.  If that is the case, I should be able to apply an external clock to the chip and get it back.  The other option is to use high voltage programming which should be able to recover from any of these states and get the fuses back to a coherent state.

So, my next project will be to build a high voltage programming setup.  Oh sigh...  Probably just as well as I need to build one of these HVSP (High Voltage Serial Programming) jigs eventually anyway... 

Sunday, April 10, 2011

Working with new tool chain

As the Arduino beacon project has progressed, I have spent some time trying to minimize the code size.  For one thing, there are a number of components that the beacon project does not need that are drug into the final image.  To do this I have moved away from the Arduino IDE for development of this project.  I am using the GNU AVR tool chain now.  I copied all the headers and code files from Arduino install and have been modifying them to eliminate components that I do not need.  For example I don't need the serial port stuff, string classes, interrupt classes, etc.  Rather than use generic port libraries, I am moving to talk directly to the ports instead.  These kinds of changes have netted me 6-8 kb of space savings.  I need to hack on the wire libraries to eliminate the stuff I am not using.  Lastly, the Arduino boot loader is no longer necessary as I am using an in-circuit programmer (usbTinyISP) from the good folks at AdaFruit.  This saves another 0.5 kb at the upper end of flash.  The optiboot boot loader is pretty small, but others are not so compact.  All things considered, the savings in code size are significant.  Lastly, the tool chain is available for Windows, Linux and Mac platforms, so I think I will stick with it.

Converting from Arduino IDE is pretty straight forward:

1. Add #include "WProgram.h" to the top of your sketch.
2. Add a main() function at the bottom that calls setup() and loops calling loop() infinitely.
3. Provide forward declarations for all of your functions.
4. Create a Makefile to drive the build process if desired (recommended).

I copied all the components from my project into a new folder and built a Makefile to compile and link everything.  Now I can hack on the Arduino components referenced in my Beacon project without affecting my Arduino IDE environment.

Saturday, April 2, 2011

New RTC and data logging shield for beacon project

I have built one of the fine data logging shields for Arduino from the fine folks at Adafruit to further clean up my beacon project rats nest.  The new setup looks like this attached to my Arduino Uno.
I need to add a socket for the DDS-60 and a couple headers to bring data GPIO lines out.  The real-time clock has been tested and is functional.  This should be my final setup until a PCB is created for this project.

Thanks for all the emails!

I created this blog originally as a place to catalogue my ramblings and notes for myself.  I have been receiving quite a bit of email from around the world however expressing interest in the project, the code, hardware details and interest in the software.  While the project is not yet to a place where I am ready to publish details, that is the long-term plan.

I am however happy to help in any way I can anyone with a similar interest in this kind of project and have had some fun email exchanges as a result.  I appreciate all the offers to help from many folks as well.

I invite anyone with comments or suggestions to email or more ideally to post comments on the blog so that everyone can benefit from the discussion.  I will initially opt to not post emails as I want to respect the privacy of those involved unless explicit permission is provided to post those emails.

Trying to spruce up the Arduino beacon project

The Arduino WSPR/QRSS beacon project has gotten to the point where it is time to try and get rid of some of the rats nest of the breadboard nature of the project so far.  To that end, I have mounted the controls and display in a panel.

Next, I will be eliminating the breadboard and using a data logger shield for the Arduino.  This shield has an SD card slot (which I do not need) as well as the same real-time-clock (RTC) I chose for my beacon project the DS1307.  There is also some breadboard space available to mount a socket for the DDS-60 and any other associated discrete components I may need.  This should tidy things up sufficiently to allow the software components to be finalized.

After the software bits are complete (as much as any software project ever is) I will be producing a PCB for the entire project.

So far, my project has grown a bit bloated as I have allowed myself to be sidetracked on numerous occasions by additional modes such as Feld Hell.  I have added some test code to experiment in geneating Hellschrieber-like displays on a QRSS waterfall such as we have in Spectran or Argo.  The resultant bloat has put the code size beyond the code size limit of the ATMega168.  Since I am using an Arduino Uno with the 328 chip, this has not been a problem, but it does increase the expense of this project for others to duplicate or leverage the code.  I will have to work on that and will try to get the code size as small as possible in the final versions.  Things like my choice to do frequency calculations for the DDS using 64 bit integers has no doubt drug in the entire 64 bit math library whereas I only need one operation.  Obviously many opportunities exist for further optimization.