On Fri, Feb 19, 2016 at 05:56:04PM -0500, Daniel Franke wrote: > At a high level, a clock is characterized by the answers to three questions:
I guess that should be four ... > # II - What drives it? > > A typical PC has several oscillators. In addition to the main one, > which sends clock interrupts to the CPU, there's likely to be a > separate one on each NIC (important for PTP), one driving the RTC (aka > BIOS clock), and perhaps an external oscillator providing a PPS > signal. You're missing at least a few ones here that are available on typical PC hardware, including the pit, hpet, tsc, ACPI timer. > * CLOCK_MONOTONIC_RAW is an atomic clock with an unspecified epoch and > a precision of one nanosecond. It is driven by the system oscillator. > It supports no adjustments at all. It is corrupted by suspending or > rebooting the machine. I'm sure what you mean by corrupt in the case of suspending. It's still measuring something, but maybe not something you (or ntp) cares about. I guess this falls under your category of "clocks that count time selectively". Also, the 1 nanosecond might not be the resolution. It's going to depend on the system. You need to call clock_getres() to find out what the real resolution is. But 1 nanosecond is the best you can expect. > * /dev/rtc0 is a clumsy clock with a specified epoch and a precision > of one second. It is driven by the RTC oscillator. It supports > stepping. It is corrupted only by the death of the CMOS battery. It actually supports various frequencies. There is also at least /dev/hpet that you might want to look at. Kurt _______________________________________________ devel mailing list devel@ntpsec.org http://lists.ntpsec.org/mailman/listinfo/devel
