Add partially complete wildcard page

content/14_wildcard.md

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+title = "Wildcard"
+date = "2018-12-05"
+menu = "main"
+weight = 16
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+
+Files: [audio_interface_2.sch](/designs/13_audio_interface_2.sch) [audio_interface_2.brd](/designs/13_audio_interface_2.brd) [lufa](https://gitlab.cba.mit.edu/erik/lufa) (see Demos/Devices/ClassDriver/MIDI and Demos/Devices/ClassDriver/AudioInput)
+
+This week there's a lot on the menu: soft robotics, bioprinting, coil plotting, wire EDM, and many more. I'd like to learn them all, but for now I'll continue my exploration of [LUFA](http://www.fourwalledcubicle.com/LUFA.php). So far I have a virtual serial port example working, but let's see what else I can do. Throughout I'll be using the board that I designed and fabricated [last week](../13_networking).
+
+
+## MIDI
+
+In [outputs week](../10_output_devices) I taught an ATtiny44 to speak MIDI, albeit not perfectly. Now I can try on an XMEGA. I should also be able to ditch the FTDI cable and [special software](http://projectgus.github.io/hairless-midiserial/), since everything should work over USB using standard device drivers.
+
+Luckily LUFA has a MIDI device example. To make it work with my board I followed the same steps I previously used for the [virtual serial port](../13_networking) example.
+
+When I plug it in, it shows up as "LUFA MIDI Demo" in Apple's system MIDI configuration utility.
+
+![](/img/14_midi_setup.png)
+
+It's also recognized by [Logic Pro](https://www.apple.com/logic-pro/) and [Ableton Live](https://www.ableton.com/en/live/). So I can use it to control software instruments in all my usual environments. I definitely won't be using the FTDI cable for MIDI anymore.
+
+![](/img/14_midi_logic.png)
+![](/img/14_midi_live.png)
+
+
+## Audio
+
+This is what I'm ultimately after for my final project, but it's going to be a lot trickier. LUFA's AudioInput example isn't configured to support XMEGAs, so I either have to redo my board with a different microcontroller, or dive deep into LUFA and add the missing functionality for XMEGAs. The former is a bounded problem, but the latter is a lot more educational. So down the rabbit hole I go...
+
+To begin I cleared out the LUFA LED, Button, and ADC code since they're either not defined for XMEGAs or not something I want to use. When building I still immediately get an error that XMEGA is not a supported architecture. I fixed this by editing `Config/LUFAConfig.h`. I took the following values from the MIDI example's config file.
+
+{{< highlight c >}}
+	#if (ARCH == ARCH_AVR8)
+
+        // ... existing AVR config code here ...
+
+    #elif (ARCH == ARCH_XMEGA)
+
+		#define USE_STATIC_OPTIONS               (USB_DEVICE_OPT_FULLSPEED | USB_OPT_REG_ENABLED | USB_OPT_AUTO_PLL)
+		#define USE_FLASH_DESCRIPTORS
+		#define FIXED_CONTROL_ENDPOINT_SIZE      8
+		#define FIXED_NUM_CONFIGURATIONS         1
+		#define MAX_ENDPOINT_INDEX               2
+
+	#else
+{{< /highlight >}}
+
+Now the compiler complains about invalid registers. Progress! To fix this I need to figure out what the registers they use do on smaller AVR boards, then implement the same thing for XMEGA.
+