> >> [] > >>> To timestamp the pps, you have to have some module (ie kernel level) > >>> timestamp process. shmpps, gpsd, the kernel pps, write your own,.... > >> > >> Thanks for the information, Bill. My only additional comment is that > >> the code to timestamp the PPS /can/ be in user-mode, although > >> kernel-mode is preferable. Additional Linux modules are /not/ required. > > > > ?? To timestamp the interrupt, you need kernel land. Ie, you need a > > module. Now you can use one of the modules others have written or you > > can write your own. But userland cannot get any sort of accuracy trying > > to figure out when and if a hardware line has been pulled up or not. > > You may think that, but gpsd does it that way and it works surprisingly > well.
I'm not entirely sure of that. On Linux it uses the kernel pps-api. So the kernel makes a note when an interrupt came in and gpsd requests these values from the kernel. That's why it opens /dev/ppsX Folkert van Heusden -- www.TrustedTimestamping.com is a service that enables you to show that at a certain point in time, you had access to a hash-value reflecting the contents of a file (this file can be a word document, a jpeg image, everything). ---------------------------------------------------------------------- Phone: +31-6-41278122, PGP-key: 1F28D8AE, www.vanheusden.com _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
