M. Warner Losh wrote: > In message: <[EMAIL PROTECTED]> > Christian Vogel <[EMAIL PROTECTED]> writes: > : For example, do you want to timestamp interrupts to synchronize > : machinery? Or just note down the timestamps of bittorrent downloads very > : precisely? Just synchronizing an otherwise idling computer is probably > : much easier than a machine that is doing a lot of additional work that > : can mess up the timekeeping by clogging the processor or just creating > : varying stress on the power-supply lines. > > That's the real question. Like I said before, when you are down to > the microsecond level, what good is that? The jitter from system > calls and such is going to be high enough to make that not completely > useful. And if you are trying to do things to hardware with software > that requires that level of synchronization, you aren't going to get > it without timestamping done in hardware of some mutually observable > event (pps, packets on the network, etc). > > Warner > PTP achieves submicrosecond synchronisation over small LANs without network switches. It uses hardware time stamping of LAN packets. Someone has even implemented it in software (with degraded performance). See: http://ieee1588.nist.gov/
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