It's also worth mentioning with respect to the new piece for Coachella, that I've acquired a few new tools that are making the process much quicker and easier. First and foremost, and really the centerpiece of it all, is the new Tektronix TDS3024B Oscilloscope. This baby has been on my wishlist ever since playing such a huge role in my senior design project success back at UIUC, and with the days counting down fast to Coachella, I decided I needed all the help I could get, and it really has been a big help.
I often describe working on electronics without a good scope as being comparable to trying to work with your eyes closed. It's not necessarily impossible but it increases both the time and frustration of even simple tasks by orders of magnitude. It's much easier to work intuitively when you can see what's happening right before your eyes. The image above, which I grabbed just to confirm that the duty cycle of the PWM was changing (in this design, the duty cycle of the PWM is also capable of changing faster than the eye can perceive), shows in yellow, pink, and green the CS, MOSI, and MISO lines from the FPGA to the SD card, and in cyan one of the channels of PWM out to an LED. Prior to this I had an old Tek265 analog scope which was useful in many circumstances, but for things like the serial bus debugging of the past few days, just didn't do the job. The 3024 has 4 channels @ 200MHz with all sorts of advanced measurement capabilities, FFT, advanced trigger, and a 640x480 color LCD. It also sports its own internal web server so getting screen captures is as simple as opening a web browser. The only negative is that when debugging a 50MHz serial bus on a 200MHz scope, the waves are pretty distorted, so a higher bandwidth wouldn't hurt. I wouldn't trade the advanced features for more bandwidth though, and to up the bandwidth to 500MHz crosses the line into 5-figure territory, which just wasn't in the cards this time. The reality is that the 3024 has been capable of everything I've asked, and I couldn't be more pleased with my decision on this one.
Also very helpful has been the Intronix LA1034 LogicPort USB Logic Analyzer. A logic analyzer is essentially an oscilloscope that trades the ability to see analog voltage levels for the ability to see lots of channels at once — in the case of the LogicPort, 34. It's somewhat limited in its sample storage capacity, which limits the length of data you can view at one time, but it mostly makes up for this with really smart triggering, which lets you focus that limited view on exactly what you want to see. The software also decodes serial buses, so it turns the SPI data and clock wave forms into hex that you can read directly (shown in the image below), which has been invaluable in the past few days. It's also an incredible bargain, when you compare with hardware solutions that (in Tektronix) start at $10k. The LogicPort is no $10k piece of gear, but it's a great addition to the lab that I'm very glad to have made. Plus, it's made in the USA by a small American company doing great work, which is always nice to support when the opportunity arises.