Right now, the program is controlled by three command line switches. I've created these options with a mind for expansion in the future (at least the serial flash part). Here's the help printout from the program:

Usage: avs3a [options]
Options:
  -b, --bitstream=BITSTREAM	Bitstream used to configure FPGA
  -p, --port=SERIAL-PORT	Serial port connected to eval board
  -s, --slaveser		Configure FPGA in Slave Serial mode

1. Download the source code here.
2. Unpack the archive in the location where you intend to use the program.

   tar xzvf avs3a.tar.gz

3. Change to the avs3a directory.

   cd avs3a

4. Build the program from source.

   make all

5. Make sure that your eval board is plugged into a USB port.
6. If you don't know the serial port of the eval board, then find it. I'm not sure what you will see, but on my Ubuntu Hardy box, my board enumerates as /dev/ttyACM0 or /dev/ttyACM1

   dmesg | grep tty

7. Make sure you have a bitstream file to use.
8. Issue the command to program the board

   ./avs3a -s -p /dev/ttyACM0 -b sample_bitstream.bit

If you try this and find it useful, or find a problem with the program then please, please, let me know in the comments below (or e-mail me). Thank you for testing this!

The source tarball didn't want to compile on my Ubuntu Hardy machine on the first try. It threw some cryptic errors about some of the wxWidget objects in the code. A bit of Googling and some lucky guessing enabled me to figure out that the code wanted to compile with wxWidgets 2.6, not the version 2.8 that is standard on Hardy. I forced the linker to use 2.6 and managed to get the code to compile (although it was still complaining about a few warnings). Once I got over that speed bump, the program seemed to work as advertised, with one exception. As you can see in the attached screenshot, something is seriously wrong with the spectrum display. For some reason, the program is drawing vertical lines across the entire spectrum where there should be nothing. Since I had access to the code, I thought that maybe I would give a shot a locating any glaring problems that might be causing this. I know a bit of C++, but have very little experience in coding for *nix machines, and know virtually nothing about wxWidgets. However, the code to draw the spectrum display seemed fairly obvious and I couldn't find anything wrong with it. You can still see a signal on the display if you look hard enough, but its very difficult to tell with all of the offending vertical lines. My best guess is that something is wrong in the array which holds the FFT data plotted by the spectrum display, but that's only a guess. I just don't have the expertise or the proper tools to properly debug this type of problem.

Ignoring that flaw, this is otherwise a really neat program. The syntax is very simple and allows you to easily try different processing concepts in just a few lines of code. There are two special variables that get used in every script: in and out. The in variable represents the data flowing into BasicDSP from the chosen source, while out is the variable that you send your processed data to in order to output it to the speaker. The simplest script that you can write for BasicDSP is a passthrough function, where no processing of the data is performed:

out = in

In the above example, each sample is directly passed to the output. If you could not hear the output very well, you can amplify the signal by performing multiplication with a constant.

out = in * 100

By multiplying the sample by 100, you are increasing the signal level by 40 dB.

There are four slider controls which are accessible via variable (slider1 - slider4). These allow you to dynamically alter variables in the script. For example, if you wanted to be able to change the signal level with a slider, it's a simple as:

out = in * slider1

There are other special variables and functions included in the scripting language that help to enable common DSP tasks. These can all be put together to create simple circuit blocks like low-pass filters, up to more complex tasks like quadrature receivers. A basic direct conversion receiver can be put together quite simply using these functions. The following code (taken from a reprint of a SPRAT tutorial) implements the DC receiver in code by creating a sawtooth oscillator (in lines 2 & 3), mixing the input signal to baseband (just a simple multiplication at line 4), then sending the signal through two stages of low-pass filtering (lines 5 & 6).

1
2
3
4
5
6
7

samplerate = 48000
sawtooth = mod1(sawtooth+slider1)
osc = sin1(sawtooth)
mix = osc * in
lpfa = lpfa + slider2*(mix-lpfa)
lpfb = lpfb + slider2*(lpfa-lpfb)
out = lpfb

There's some more information on the program and some good example code on the website of PE1OIT. If you have even a small bit of interest in the inner workings of a SDR receiver, you owe it to yourself to download this software and try it out.

However, I recently ran across this posting when browsing the AVR Freaks forum. The author kindly gives instructions on how to set up the Eclipse IDE for use in AVR development on the Ubuntu platform. This looked really promising, since I've always been a sucker for nice IDEs (yes, I know that probably lowers my geek cred a few notches). So I gave it a go and found that the instructions worked nearly flawlessly. The only hiccup I encountered was at the very end of the build process when Eclipse was waiting for the sudo password for avrdude (oddly enough, you have to run avrdude as root to access the USB programmer, unless you implement a little workaround that I'll show you in a second). I didn't see any way to enter the root password into a terminal, so I had to cancel the whole process.

A bit of thought and much more searching brought me to the answer to the problem. There is a way to get non-root access to the USBtinyISP. You have to create a udev rule to tell the kernel to change permissions on the USBtinyISP. The documentation on the ladyada website tells you to do this, but it only gives you half of the story. First of all, it doesn't mention exactly where to place the new rule that you are creating. Her documentation stated that I needed to put the rule in a file in /etc/udev/rules.d/. The problem is that this doesn't state whether I need to place the rule in an existing file or create a new one. After a bit of trial-and-error and yet some more Google searching, I found out that I needed to create a new file for the USBtinyISP. So a new file named 50-usbtinyisp.rules was created. The other problem is that the actual rule given on the ladyada site seems to have a typo in the MODE parameter. Comparing this rule to some other rule examples, it appears that the correct rule is:

SUBSYSTEM=="usb", SYSFS{idVendor}=="1781", SYSFS{idProduct}=="0c9f", GROUP="users", MODE="0666"

Once you get the udev rule set up correctly, you no longer need root to access the USBtinyISP, and the entire build process in Eclipse works flawlessly.

So far, using Eclipse as an AVR development platform has been a real pleasure. There's a lot of nice little touches, like having quick access to all of the special function registers of each device and easy configuration of the build parameters via GUI. If you are like me and like the convenience that an IDE gives you, then the AVR/Eclipse environment is an excellent choice, and may even be better than WinAVR.