Even though the jitter due to USB1.1 may be 1ms, NTP can reduce its effect significantly. And USB2.0 reduces this anyway.
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| @@ -72,8 +72,11 @@ PPS with USB to serial devices · 71 unmodified lines | |||
| 72 | It is possible to grab the PPS from an USB to serial device. However, | 72 | It is possible to grab the PPS from an USB to serial device. However, |
| 73 | you should take into account the latencies and jitter introduced by | 73 | you should take into account the latencies and jitter introduced by |
| 74 | the USB stack. Users have reported clock instability around +-1ms when | 74 | the USB stack. Users have reported clock instability around +-1ms when |
| 75 | synchronized with PPS through USB. This isn't suited for time server | 75 | synchronized with PPS through USB. With USB 2.0, jitter may decrease |
| 76 | synchronization. | 76 | down to the order of 125 microseconds. |
| 77 | |||
| 78 | This may be suitable for time server synchronization with NTP because | ||
| 79 | of its undersampling and algorithms. | ||
| 77 | 80 | ||
| 78 | If your device doesn't report PPS, you can check that the feature is | 81 | If your device doesn't report PPS, you can check that the feature is |
| 79 | supported by its driver. Most of the time, you only need to add a call | 82 | supported by its driver. Most of the time, you only need to add a call |