Nick Hudson <skrll%netbsd.org@localhost> writes: > On 07/25/14 17:13, Greg Troxel wrote: >> Module Name: src >> Committed By: gdt >> Date: Fri Jul 25 16:13:21 UTC 2014 >> >> Modified Files: >> src/share/man/man4: ucom.4 >> src/sys/dev/usb: ucom.c >> >> Log Message: >> Add PPS support to ucom(4). >> >> This is basically cribbed from regular serial ports, and just adds >> hooks to call the pps support routines. >> >> Also, note in the ucom(4) man page that there is about 1 ms of >> latency. Discussed on tech-kern in October of 2013, with the only >> concern being that someone who didn't know what they were doing might >> set up a stratum 1 server, and that somehow might have worse >> timekeeping than whatever else that person might have done; the man >> page comment is a mitigation for this. > > latency of 1ms and the same jitter - only ucycom uses interrupt > endpoints for data transfer I was abstracting on purpose, because no other man page describes performance characteristics in such detail. (When I tested, my best guess was that the delay from PPS edge capture ranged from 400us to 1400us as the USB frame clock shifted.)
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