On Tue, 2017-01-31 at 22:59 -0800, Hal Murray wrote: > Thanks. > > b...@kernel.crashing.org said: > > Right, we just use the value provided by Open Firmware. Any chance you can > > try with MacOS X ? > > Not easily. I'm using boxes from eBay. They didn't come with CDs and I've > already installed other software.
Ok, I do have one though somewhere with OS X on it. If you give me instructions on how to test (I know near to nothing about ntpsec), I should be able to compile and run it. > > > From the value in the properties you showed me (and the ones I have in some > > DT snapshots) it looks like the value isn't fixed but somewhat calibrated by > > Open Firmware during boot. > > I rebooted several times. It always got the exact same clock speed numbers. Interesting. Though different units get different numbers... > I don't know anything about the insides of the PowerPC chip. Can you confirm > that the kernel time keeping works off an always ticking register similar to > the Intel TSC and uses the timebase-frequency as the scale factor? It should be externally clocked on these CPUs. Either that or a divisor of the bus frequency, I don't remember, but I *think* Apple uses an external clock. But yes, the timebase is supposed to be always running at a constant speed which is the timebase-frequency (no scaling, the register is always running at *that* speed). > If so, I should be able to "fix" it from Open Firmware. I tried that but > things got worse. I could easily have fatfingered something but more likely > my reasoning for computing the right value was buggy. I guess I'll try again. > > I see that powerpc/kernel/time.c reads both timebase-frequency and > clock-frequency, but doesn't seem to use clock-frequency. Was that just a > handy place to read it that got called before anybody else needed it? Right, it's for display in /proc/cpuinfo in absence of a specific frequency control driver for the platform (there should be one for the mac mini though). Cheers, Ben.
