On Tue, Oct 20, 2015 at 12:11 PM, Thomas Gleixner <t...@linutronix.de> wrote: > On Tue, 20 Oct 2015, Richard Cochran wrote: >> On Tue, Oct 20, 2015 at 01:51:13PM +0200, Richard Cochran wrote: >> > You can, in fact, achieve "proper" correlation by sampling. As John >> > said, the question is whether the method in the patch set "measurably >> > improves the error" over using another, simpler method. >> >> Here is a short example to put some numbers on the expected error. >> Let the driver sample at an interval of 1 ms. If the system time's >> frequency hasn't changed between two samples, A and B, then the driver >> may interpolate without introducing any error. > > Darn, we don't want to have that kind of sampling in every driver > which has this kind of problem even if it looks like the simpler > choice for this particular use case. This is going to be something > which next generation chips will have on more than just the audio > interface and we realy want to have a generic solution for this.
I sort of agree with Richard that the timekeeper history approach doesn't seem like a generic solution here. And again, you seem to be speaking with a bigger picture in mind that at least I don't yet share (apologies for being thick headed here). Being able to have various hardware sharing a time base is quite useful, and methods for correlating timestamps together are useful. But I don't yet really understand why its important that we can translate a hardware timestamp from some time in the past to the correct system time in the past without error. thanks -john -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
