frequency table:
---------------


equal tempering:
  x = 2 ^(1/12)
octave is 8 below middle A (440Hz)
  c = (440 / (x^9)) / 8
counter value (complement of period)
  p = -1 -(8000 / c * x^(-0))



communication
-------------

i was thinking about a bitbanged serial interface,
where the synth runs at 9600 hz, and the timing engine
is used to send/receive asynchronous serial data:

* interrupt on change isr
* wait loop until middle of start bit,
  guess where we are by looking at timer0 value
  (interrupt was probably pending)
* check start bit
* ok -> push 'receive synth'

receive synth: recv 9 bits. when stopbit is
valid, save data in buffer.



now, i was thinking that a simpler, and way cooler,
solution is to use a 2 wire protocol: master sends
out a 8kHz clock signal, slave can sync its sample
clock to this (alternative up/down edges).

once this is in place, they can start sending meaningful
data to each other, using their audio in/out lines. using
'magic numbers' it should be possible to:

* avoid a master ever sends out a magic number without intent
* enable the slave to switch into receive mode

this is to make sure plain transmission/reception works. when
you move this stuff through audio processors, weird things
might happen.

to get this working:
* receive should be always on, so if a processor gets confused,
it can always be reset by sending it a magic value and a reset
command.