... | @@ -36,6 +36,27 @@ Absolute calibrated devices can be used as "golden standards" for the |
... | @@ -36,6 +36,27 @@ Absolute calibrated devices can be used as "golden standards" for the |
|
[relative calibration
|
|
[relative calibration
|
|
procedure](https://www.ohwr.org/project/white-rabbit/wikis/Calibration).
|
|
procedure](https://www.ohwr.org/project/white-rabbit/wikis/Calibration).
|
|
|
|
|
|
|
|
Precision Time Protocol (PTP) packets that are used for the link delay
|
|
|
|
calculation are timestamped inside WR devices and hence are defined on
|
|
|
|
the “internal time” scale (the red arrow in Figure 2). Delays exist
|
|
|
|
between the internal time scale and the electrical interfaces that are
|
|
|
|
defined on the “external time” scale (the blue arrow in Figure 2).
|
|
|
|
The external time scale uses the PPS signal as a time reference point
|
|
|
|
(t=0). The time it takes for a t1 timestamped Tx packet to traverse the
|
|
|
|
external electrical reference plane is:
|
|
|
|
|
|
|
|
- Δ <sub>TXcal</sub> = A - t <sub>1</sub> = Δ <sub>PPS</sub> + Δ
|
|
|
|
<sub>tx</sub>
|
|
|
|
|
|
|
|
When applying a loopback from Tx to Rx then:
|
|
|
|
|
|
|
|
- Δ <sub>RXcal</sub> = B - t <sub>4p</sub> = Δ <sub>PPS</sub> + Δ
|
|
|
|
<sub>rx</sub>
|
|
|
|
|
|
|
|
defines the time it takes for a t4p timestamped Rx packet to traverse
|
|
|
|
the external electrical reference plane. Note that t4p includes fine
|
|
|
|
delay phase information.
|
|
|
|
|
|
time-scales.png
|
|
time-scales.png
|
|
*Figure2: Time scales and their relations**
|
|
*Figure2: Time scales and their relations**
|
|
|
|
|
... | | ... | |