Add photo of test rig and some description of the test outcome.

README.md

@@ -8,5 +8,34 @@ noise generator and duty cycle control, amongst other things.
 This Arduino sketch tests an AY8930 chip by setting up some initial configuration and generating sounds.
 The Arduino's ADC (analog-to-digital converter) is used, along with a pot, to control the sound generator.
 
+## Test Plan
+We want to verify both that the chip works and that it has the
+enhanced functionality (i.e. that it really is an AY8930).
+So the Arduino sketch switches the chip into enhanced mode by setting the
+upper four bits of the ENVELOPE register (R13) to 1010 or 1011.
+The function 'aywrite()' that accesses the chip must keep track of
+which bank is selected and change banks if required to allow us to set
+up registers beyond the 16 of the AY-3-8910.
+'aywrite()' takes register numbers from 0 to 31, with 0-15 being in
+Bank A and 16-31 being in Bank B.
+
+Once we can use the enhanced features of the AY8930, we set it up
+in such a way that listening to the output will demonstrate that it
+has more than one envelope generator.
+Channel A is set up to produce a tone, and Channel B produces noise.
+Both channels are fed through envelope generators set to produce a
+triangle-wave envelope (rampling up and down alternately).
+Channel A tone frequency and envelope period are controllable via
+pots connected to the Arduino analog inputs 0 and 1.
+Channel B envelope period and noise parameters are fixed.
+
+When the sketch runs, we should hear a pulsating tone and a pulsating
+noise.
+Only the tone should be controllable by the pots; the noise should
+be unaffected.
+
 ## AY8930 Chip
 ![AY8930 chip](AY8930.jpg "AY8930 chip")
+
+## AY8930 on Breadboard
+![AY8930 rig](AY8930_rig.jpg "AY8930 rig")