TRNG by hamming distance of processor tics
You are talking about using the relative jitter of 2 timers to source entropy.

That is indeed an option for entropy generation. 

However in terms of cryptographically secure RNGs (the reason you would go to such length to create randomness) this jitter can be influenced by the load on the processor and electrical noise. This provides a side channel to try and influence or predict the entropy used for the generator.