-------- In message <20160327130706.ga1...@kib.kiev.ua>, Konstantin Belousov writes:
>> I haven't seen a single (hardware) system since I started measuring >> this 15-20 yeas ago on which the i8524 is not fed from the same clock >> as the TSC. A very important and relevant detail here is that the *only* clock/counter which has a standardized frequency *is* the i8254 counter. >RTC needs its own dedicated crystal. The RTC *crystal* may not even exist, only the RTC itself which may be driven by gremlins on a threadmill for all we care. Besides, getting hold of *precise* timing from the RTC is a nightmare, it's not meant to be used for that. >I was not able to find any specifications for allowed jitter in PCH PLLs, >but I would expect that above IDT chips have much better stability than >something in overheating PCH. Jitter requirements are pretty tight for anything you're going to PLL into the GHz range, but any quartz crystal is going to have much better phase-noise spec than anything we can measure in the digital noise of a modern computer. (Often the PLL chips modulate the quartz to spread out EMI spurs, look for "spread-spectrum" settings.) >> > some hypervisors start offering modes where old ISA peripherals >> > are not emulated, How do they expect people to run MS Flight Simulator then ? :-) >I think we have no choice but do something for ISA/LPC-less configurations. >We could even trust CPU report about its frequency as the last resort. Usually the errors will be magnificient, so a trivial sanity-check will catch them. Don't leave home without it. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
