TechnicalNotes < Dev

---+!! Technical Notes

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---++ Reading the System Clock

NTP's =sys_fuzz_nsec= is the time it takes to read the clock in nanoseconds (it's an integer type), and =sys_tick= is the same thing in a floating type but in usec.  =sys_precision= is log2 of =sys_tick=.

Some systems have =clock_getres()= and it behaves differently on different OSes.  NTP generally uses =CLOCK_REALTIME= for its operations, but on some OSes that value will not give use the information we want:

| *OS* | *sys_fuzz_nsec* | *sys_tick* | *CLOCK_REALTIME* | *Other* |
| !FreeSBD7 |  1676 |  1.676 |  280 | |
| Solaris10 |  916 |  0.916 |  1000000 |  83 =CLOCK_HIGHRES= |

This topic: Dev > WebHome > TechnicalNotes
Topic revision: r1 - 2012-12-27 - 08:13:08 - HarlanStenn