Commit dbe913c8 authored by Benoit Rat's avatar Benoit Rat

doc: improve GM explanation

parent 5cb03930
......@@ -1476,27 +1476,33 @@ The requirement for the applied signals are:
[^aroundval]: These values are given on an indicative basis because they depend on the source and
connection you are using.
### Example from GPS
### Using a GPS
The common way to use grandmaster mode is with a GPS source where the
input 10MHz signal can be square or sinusoidal.
![Grandmaster signals from GPS (PPS=>Yellow, 10MHz=> Blue)](img/ssk_gm_GPS.jpg)
When the GrandMaster is a [SPEC+FMCDIO] `PPS_in` pulse serves to *mark* which rising edge of the 10MHz signal is considered the first one valid for a new second: the `PPS_out` will be fixed on the `10MHz_in` and not the `PPS_in`. `PPS_in` should therefore arrives at least 8ns before the `10MHz_in` clock.
### Example from a FMC fine-delay
As *1m is around ~5ns of delay*, you could use a cable with 4m to connect to `PPS_in` and a cable with 1m to connect to `10MHz`.
If you have a [FMC fine-delay] board you can generate the PPS/10MHz by
executing the following commands (using release 2014.04):
The following figure shows what kind of signals need to be provided to plug to the GM [SPEC+FMCDIO], and with which fixed delay the `PPS_out` is produced (~8ns).
![Grandmaster signals from GPS with different cables length (PPS in=>Yellow, 10MHz CMOS=> Blue, 10MHz Sin => Green, PPS out=>)](img/ssk_gm-4m1m.jpg)
### Using the fine-delay.
If you have a [FMC fine-delay] board you can generate a precise PPS/10MHz by
executing the following commands (using release v2014.04):
>:$ sudo tools/fmc-fdelay-pulse -o 1 -p ## PPS on #1
>:$ sudo tools/fmc-fdelay-pulse -o 2 -1 ## 10MhZ on #2
>:$ sudo tools/fmc-fdelay-pulse -o 1 -r 1s-10n -T 1s ## PPS on #1 (10ns before 10MHz).
>:$ sudo tools/fmc-fdelay-pulse -o 2 -1 ## 10MhZ on #2
![Grandmaster signals from a FMC fine-delay (PPS=>Yellow, 10MHz=> Blue)](img/ssk_gm_fdelay.jpg)
### Locking
### Locking GM PLL to external 10MHz/PPS
Then in the wrc console of the [SPEC+FMCDIO] just execute the following commands:
......@@ -1640,7 +1646,6 @@ To ease the communication using etherbone, we have added the `` tool in
folder that access through the etherbone library to the device and perform
read/write operations.
Below we display a quick example on how to use it.
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