Mirage_crypto_rng_mirageval initialize : 
  ?g:'a ->
  ?sleep:int64 ->
  'a Mirage_crypto_rng.generator ->
  unit Lwt.tinitialize ~g ~sleep generator sets the default generator to the generator and sets up periodic entropy feeding for that rng. This function fails (Lwt.fail) if it is called a second time. The argument ~sleep is measured in ns, and used as sleep between cpu assisted random number collection. It defaults to one second.