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Diffstat (limited to 'Documentation/pps/pps.txt')
| -rw-r--r-- | Documentation/pps/pps.txt | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt index d35dcdd82ff6..c03b1be5eb15 100644 --- a/Documentation/pps/pps.txt +++ b/Documentation/pps/pps.txt @@ -66,6 +66,21 @@ In LinuxPPS the PPS sources are simply char devices usually mapped into files /dev/pps0, /dev/pps1, etc.. +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 has reported clock instability around +-1ms when +synchronized with PPS through USB. This isn't suited for time server +synchronization. + +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 +to usb_serial_handle_dcd_change after checking the DCD status (see +ch341 and pl2303 examples). + + Coding example -------------- |