divisor to calculate the channel ratio
and slightly better computer side code

Signed-off-by: Leo Bärring <leo.barring@gmail.com>
binary division, usart improvements, i2c refactoring/cleanup

* implementation of binary division seems to work
* better usart data write functions
* cleanup/refactoring of i2c test code code into callable
  functions and less direct use of magic numbers

Signed-off-by: Leo Bärring <leo.barring@gmail.com>