Even though the jitter due to USB1.1 may be 1ms, NTP can reduce its effect significantly. And USB2.0 reduces this anyway.
Unified · Split
| @@ -72,8 +72,11 @@ PPS with USB to serial devices · 71 unmodified lines | ||
| 72 | 72 | It is possible to grab the PPS from an USB to serial device. However, |
| 73 | 73 | you should take into account the latencies and jitter introduced by |
| 74 | 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 | |
| 76 | −synchronization. | |
| 75 | +synchronized with PPS through USB. With USB 2.0, jitter may decrease | |
| 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 | 81 | If your device doesn't report PPS, you can check that the feature is |
| 79 | 82 | supported by its driver. Most of the time, you only need to add a call |