What Is Incremental Checkpoint In Oracle?

In my view
it occurs
* every 3 second
* during log switch
depending on parameter value
like 1. Fast_start _mttr_target.
  2. Fast_start_io_target  etc.
*  database writer  write all dirty buffer generated after the last checkpoint.
*  checkpoint write to only control file except log switch.
*  during log switch checkpoint write to both control file and data file  header.