package core_unix

A calibrator contains a snapshot of machine-specific information that is used to convert between TSC values and clock time. This information needs to be calibrated periodically such that it stays updated w.r.t. changes in the CPU's time-stamp-counter frequency, which can vary depending on load, heat, etc. (Also see the comment in the .ml file.)

Calibration at the rate of 0.1, 1 or 2 secs produces errors (measured as the difference between Time.now and the reported time here) on the order of 1-2us. Given the precision of 52-bit float mantissa values, this is very close to the least error one can have on these values. Calibration once per 10sec produces errors that are +/-4us. Calibration once per minute produces errors that are +/-15us and calibration once in 3mins produces errors +/-30us. (It is worth remarking that the error has a positive bias of 1us -- i.e., the error dances around the 1us mark, rather than around 0. It is unclear where this bias is introduced, though it probably does not matter for most applications.)

This module maintains an instance of t internal to the module. The internal instance of t can be updated via calls to calibrate (), i.e., without specifying the t parameter. In all the functions below that take an optional Calibrator.t argument, the internal instance is used when no calibrator is explicitly specified.