Even though the jitter due to USB1.1 may be 1ms, NTP can reduce its effect significantly. And USB2.0 reduces this anyway. Signed-off-by: Sanjeev Gupta <ghane0@xxxxxxxxx> --- Documentation/pps/pps.txt | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt index a9f53bb..719c974 100644 --- a/Documentation/pps/pps.txt +++ b/Documentation/pps/pps.txt @@ -72,8 +72,11 @@ PPS with USB to serial devices It is possible to grab the PPS from an USB to serial device. However, you should take into account the latencies and jitter introduced by the USB stack. Users have reported clock instability around +-1ms when -synchronized with PPS through USB. This isn't suited for time server -synchronization. +synchronized with PPS through USB. With USB 2.0, jitter may decrease +down to the order of 125 micro-secs. + +This may be suitable for time server synchronization, with NTP, because +of its under-sampling and algorithms. If your device doesn't report PPS, you can check that the feature is supported by its driver. Most of the time, you only need to add a call -- 2.10.2 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
