A down counter running at the ROSC frequency which counts to zero and stops. To start the counter write a non-zero value. Can be used for short software pauses when setting up time sensitive hardware.
The FREQA & FREQB registers control the frequency by controlling the drive strength of each stage The drive strength has 4 levels determined by the number of bits set Increasing the number of bits set increases the drive strength and increases the oscillation frequency 0 bits set is the default drive strength 1 bit set doubles the drive strength 2 bits set triples drive strength 3 bits set quadruples drive strength
This just reads the state of the oscillator output so randomness is compromised if the ring oscillator is stopped or run at a harmonic of the bus frequency