Unruh wrote: > [EMAIL PROTECTED] (Hal Murray) writes: >>You can build a clock into the network adapter and sync it up to the >>system clock. > > And how do you sync it up to the system clock without going through the > kernel, etc?
Maybe it's better to do it the other way round, i.e. sync the system clock to the NIC's timestamp counter. > Ie, I have a clock on my gps receiver that is good to 100ns. > It links to the system clock via interrupts and ntp. You have to do > something like that if you are going to sync the clock on your nic to the > system clock as well. Ie, I see no advantage to this procedure over > putting in a cheap gps clock on each of the computers and just using that > ( or running a buffered PPS line from one gps receiver to each of the > machines (using some of the spare lines in a Cat5e cable if need be).Sure > sounds cheaper than special nic cards with high accuracy on board clocks! Just like an NTP server a PTP/IEEE1588 grandmaster can synchronize a huge number of clients. Depending on the application this can either be the "official" UTC time, or just the "same" time for all devices. The target for PTP is more in industrial applications, where you have a dedicated network environment and more and more embedded devices which can be synchronized with high accuracy. For example, the new LXI standard (Lan EXtensions for Instrumentation, see http://en.wikipedia.org/wiki/LXI) which is a LAN-based successor to the old GPIB bus, explicitely uses PTP/IEEE1588 to time-trigger measurements accurately in spite of network latencies. There are now NIC chips available which support PTP timestamping, and in many measurement instruments there is a good oscillator which can be used both for time stamping and implementation of the system clock. Those devices normally have special printed circuit boards and dedicated software which supports that on-board hardware. So this is different from using PTP to synchronize a standard PC where you don't know which OS or version of an OS is running, and which types of hardware (e.g. NICs) are installed, and how to synchronize the system time to the counter chain on a PCI card or whatever. Martin -- Martin Burnicki Meinberg Funkuhren Bad Pyrmont Germany _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
