On 2011-12-24, Chris Albertson <[email protected]> wrote: > On Fri, Dec 23, 2011 at 5:51 PM, Mike S <[email protected]> wrote: >> At 01:58 PM 12/23/2011, Chris Albertson wrote... >> >>> But there is no hop of doing uS >>> level over the gigabit either net. >> >> >> IEEE 1588. > > Seem 1588 can work at the sub uS level but actual real-work software > on Linux works at the "tens of uS" level. The limiting factor is the > hardware's ability to time stamp eithernet packets. If you have > special hardware you can get to sub-uS but not using PTPd on Linux or > BSD.
If you really go to stamping the interrupt directly as it comes in on the kernel level, rather than waiting for a driver (eg the serial driver) to report that the itnerrupt has occured to userland, you can get it down to 1-2us. > > Linux's and BSD's time stamper for the PPS interface works better > (less jitter) then its time stamper for Ethernet. > > In a standard Cat-5 cable there are 8 wires in 4 pair. Ethernet only > uses 2 pair. I simply used a "spare" pair for a pulse. The parts > required cost under $5 assuming you have tools to build cables already > or old cables you can hack. > > _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
