Added comments to example sketch

Author: mhord

Arduino/Libraries/MiniGen/Library_Test/Library_Test.ino

@@ -1,26 +1,85 @@
+/******************************************************************************
+Library_Test.ino
+Library test file for the MiniGen library.
+Mike Hord @ SparkFun Electronics
+6 May 2014
+https://github.com/sparkfun/MiniGen
+
+This is a simple test/example file for the MiniGen board and library.
+
+The MiniGen is a Pro Mini shield-type board (although it can be used as a 
+standalone product as well) that generates sine, square and triangle waves up
+to a frequency of approximately 3MHz; above 3MHz, you'll start to see rolloff
+as the anti-aliasing filter on the output begins to affect the signal. Expect
+a peak-to-peak amplitude of about 1V and a DC offset of Vcc/2.
+
+Resources:
+Uses the MiniGen library and the built-in SPI library.
+
+Development environment specifics:
+Code developed in Arduino 1.0.5, on an Arduino Pro Mini 5V.
+
+This code is beerware; if you see me (or any other SparkFun employee) at the
+local, and you've found our code helpful, please buy us a round!
+
+Distributed as-is; no warranty is given.
+******************************************************************************/
+// Due to limitations in the Arduino environment, SPI.h must be included both
+//  in the library which uses it *and* any sketch using that library.
 #include <SPI.h>
 #include <MiniGen.h>
 
+// Create an instance of the MiniGen device; note that this has no provision for
+//  alternate CLK and MOSI pins, but you *can* pass it a different CS (or FSYNC,
+//  as it's referred to elsewhere) pin number.
 MiniGen gen;
 
 void setup()
 {
+  // Clear the registers in the AD9837 chip, so we're starting from a known
+  //  location. Note that since the AD9837 has no DOUT, we can't use the
+  //  read-modify-write method of control. At power up, the output frequency
+  //  will be 100Hz.
   gen.reset();
   delay(2000);
+  
+  // SQUARE is, as it suggests, a square wave. SQUARE is at the current output
+  //  frequency.
   gen.setMode(MiniGen::SQUARE);
   delay(3000);
+  
+  // SQUARE_2 is at half the normal output frequency.
   gen.setMode(MiniGen::SQUARE_2);
   delay(3000);
+  
+  // Exactly what you think it is.
   gen.setMode(MiniGen::TRIANGLE);
   delay(3000);
+  
+  // Yep.
   gen.setMode(MiniGen::SINE);
+  
+  // This needs a little explanation. The choices are FULL, COARSE, and FINE.
+  //  a FULL write takes longer but writes the entire frequency word, so you
+  //  can change from any frequency to any other frequency. COARSE only allows
+  //  you to change the upper bits; the lower bits remain unchanged, so you
+  //  can do a fast write of a large step size. FINE is the opposite; quick
+  //  writes but smaller steps.
   gen.setFreqAdjustMode(MiniGen::FULL);
 }
 
 void loop()
 {
+  // Loop is going to increase the frequency in steps of 10Hz, basically
+  //  forever. Since the upper limit is 3MHz, you'll probably not sit
+  //  around long enough for frequency to overflow.
   static float frequency = 10.0;
+  
+  // freqCalc() makes a useful 32-bit value out of the frequency value (in
+  //  Hz) passed to it.
   unsigned long freqReg = gen.freqCalc(frequency);
+  
+  // Adjust the frequency. This is a full 32-bit write.
   gen.adjustFreq(MiniGen::FREQ0, freqReg);
   delay(100);
   frequency += 10.0;