Pulse Per Second - PPS
PPS is the simplest form of synchronization. The PPS source provides a signal precisely every second. The switch is capable of using an external PPS signal to synchronize its PHC (for PPS In) and can also generate the PPS signal that other devices can use to synchronize their clocks (for PPS Out).
- In PPS In mode, the switch can use an external PPS signal to adjust the phase of its PHC. The PPS signal does not provide ToD, so Cumulus Linux uses PTP for ToD; you must configure a PTP slave port on the switch for PPS In.
- In PPS Out mode, the switch can output the PPS signal. The switch can use this signal to check the accuracy of its PHC frequency and other devices can use this signal to synchronize their PHC.
Cumulus Linux supports PPS for the NVIDIA SN3750-SX and SN5400 switches only. PPS on the NVIDIA SN5400 switch is in BETA.
Enable PPS Synchronization
To enable PPS synchronization:
Before you enable PPS In, make sure to configure a PTP slave port on the switch. See Precision Time Protocol - PTP.
cumulus@switch:~$ nv set platform pulse-per-second in state enabled
cumulus@switch:~$ nv config apply
When you enable PPS In, the PTP log reporting offset is one every two seconds instead of one every second.
cumulus@switch:~$ nv set platform pulse-per-second out state enabled
cumulus@switch:~$ nv config apply
Edit the
Default interface options
section of the/etc/ptp4l.conf
file to configure the PTP slave port on the switch. PPS In requires PTP slave port. See Precision Time Protocol - PTP for information about PTP.cumulus@switch:~$ sudo nano /etc/linuxptp/pps_out.conf ... # Default interface options # time_stamping hardware [swp29] udp_ttl 1 masterOnly 0 delay_mechanism E2E network_transport RAWUDPv4
Edit the
/etc/linuxptp/ts2phc.conf
file to set the following parameters to enable PPS In.cumulus@switch:~$ sudo nano /etc/linuxptp/ts2phc.conf # Default configurations [global] use_syslog 0 verbose 1 logging_level 6 slave_event_monitor /var/run/ptp_sem.sock ts2phc.pulsewidth 500000000 ts2phc.tod_source ptp # # servo parameters # pi_proportional_const 0.000000 pi_integral_const 0.000000 pi_proportional_scale 0.700000 pi_proportional_exponent -0.300000 pi_proportional_norm_max 0.700000 pi_integral_scale 0.300000 pi_integral_exponent 0.400000 pi_integral_norm_max 0.300000 step_threshold 0.000000050 first_step_threshold 0.000000001 max_frequency 500000000 sanity_freq_limit 0 # [/dev/ptp1] ts2phc.pin_index 0 ts2phc.channel 0 ts2phc.extts_polarity rising ts2phc.extts_correction 0
Enable and start the
ptp4l
andphc2sys
services:cumulus@switch:~$ sudo systemctl enable ptp4l.service phc2sys.service cumulus@switch:~$ sudo systemctl start ptp4l.service phc2sys.service
Edit the
/etc/linuxptp/pps_out.conf
file to set the following parameters.cumulus@switch:~$ sudo nano /etc/linuxptp/pps_out.conf # Configuration file used for the pps_out.service # It is shell formatted and the file is source'd by the service # Set the PTP device to source our PPS from. # If not specified, the service will find the first device with a clock name "sx_ptp". PTP_DEV=/dev/ptp1 # Set the pin index on the PPS device to send on. # On the NVIDIA systems, only pin 1 (0-based) is supported OUT_PIN=1 # Set the file where to cache the last started values. # This is used primarily in the "stop" operation to know what to clean up. CACHE_FILE=/var/run/pps_out # Set the out pulse charateristics for frequency and width PULSE_FREQ=1000000000 PULSE_WIDTH=500000000 PULSE_PHASE=0
Enable and start the
pps_out
service:cumulus@switch:~$ sudo systemctl enable pps_out.service cumulus@switch:~$ sudo systemctl start pps_out.service
PPS Synchronization Settings
You can configure these PPS settings:
PPS In Setting | Description |
---|---|
channel-index | Sets the channel index for PPS In. You can set a value of 1 or 0. The default value is 0. |
logging-level | Sets the logging level for PPS In. You can specify emergency , alert , critical , error , warning , notice , info , or debug . The default logging level is info . |
pin-index | Sets the pin index for PPS In. You can set a value of 1 or 0. The default value is 0. |
signal-polarity | Sets the polarity of the PPS In signal. You can specify rising-edge , falling-edge , or both . The default setting is rising-edge . |
signal-width | Sets the pulse width of the PPS In signal. You can set a value between 1000000 and 999000000. The default value is 500000000. |
timestamp-correction | Sets the value, in nanoseconds, to add to each PPS In timestamp. You can set a value between -1000000000 and 1000000000. The default value is 0. |
PPS Out Setting | Description |
---|---|
channel-index | Sets the channel index for PPS Out. You can set a value of 1 or 0. The default value is 0. |
frequency-adjustment | Sets the frequency adjustment of the PPS Out signal. You can set a value between 1000000000 and 2147483647. The default value is 1000000000. |
pin-index | Sets the pin index for PPS Out. Cumulus Linux supports only pin 1. |
signal-width | Sets the pulse width of the PPS Out signal. You can set a value between 1000000 and 999000000. The default value is 500000000. |
The NVUE CLI includes the phase adjustment
setting for PPS Out. Cumulus Linux 5.9 and later does not support this setting.
The following example configures PPS In and sets:
- The channel index to 1.
- The pin index to 1.
- The signal width to 999000000.
- The timestamp correction to 1000000000.
- The logging level to
warning
. - The polarity of the PPS In signal to
falling-edge
.
cumulus@switch:~$ nv set platform pulse-per-second in channel-index 1
cumulus@switch:~$ nv set platform pulse-per-second in pin-index 1
cumulus@switch:~$ nv set platform pulse-per-second in signal-width 999000000
cumulus@switch:~$ nv set platform pulse-per-second in timestamp-correction 1000000000
cumulus@switch:~$ nv set platform pulse-per-second in logging-level warning
cumulus@switch:~$ nv set platform pulse-per-second in signal-polarity falling-edge
cumulus@switch:~$ nv config apply
The following example configures PPS Out and sets:
- The channel index to 1.
- The signal width to 999000000.
- The frequency-adjustment of the PPS Out signal to 2147483647.
cumulus@switch:~$ nv set platform pulse-per-second out channel-index 1
cumulus@switch:~$ nv set platform pulse-per-second out signal-width 999000000
cumulus@switch:~$ nv set platform pulse-per-second out frequency-adjustment 2147483647
cumulus@switch:~$ nv config apply
To configure PPS In, edit the /etc/linuxptp/ts2phc.conf
file, then restart the PPS In service with the sudo systemctl restart ts2phc.service
command.
The following example configures PPS In and sets:
- The channel index to 1
- The pin index to 1
- The signal width to 999000000.
- The timestamp correction to 1000000000.
- The logging level to 4 (warning).
- The polarity of the PPS In signal to falling edge (
falling
).
cumulus@switch:~$ sudo nano /etc/linuxptp/ts2phc.conf
# ts2phc is enabled
[global]
use_syslog 0
verbose 1
slave_event_monitor /var/run/ptp_sem.sock
logging_level 4
ts2phc.pulsewidth 999000000
ts2phc.tod_source ptp
domainNumber 0
...
[/dev/ptp1]
ts2phc.pin_index 1
ts2phc.channel 1
ts2phc.extts_polarity falling
ts2phc.extts_correction 0
To configure PPS Out, edit the /etc/linuxptp/pps_out.conf.conf
file, then restart the PPS Out service with the sudo systemctl restart pps_out.service
command.
The following example configures PPS Out and sets:
- The channel index to 1.
- The signal width to 999000000.
- The frequency-adjustment of the PPS Out signal to 2147483647.
cumulus@switch:~$ sudo nano /etc/linuxptp/pps_out.conf.conf
# Configuration file used for the pps_out.service
# It is shell formatted and the file is source'd by the service
#
# Set the PTP device to source our PPS from.
# If not specified, the service will find the first device with a clock name "sx_ptp".
PTP_DEV=/dev/ptp1
#
# Set the pin index on the PPS device to send on.
# On the NVIDIA systems, only pin 1 (0-based) is supported
OUT_PIN=1
#
OUT_CHANNEL=1
#
# Set the file where to cache the last started values.
# This is used primarily in the "stop" operation to know what to clean up.
CACHE_FILE=/var/run/pps_out
#
# Set the out pulse charateristics for frequency and width
PULSE_FREQ=2147483647
PULSE_WIDTH=999000000
PULSE_PHASE=1000000000
Show PPS Configuration Settings
To show a summary of the PPS In and PPS out configuration settings, run the nv show platform pulse-per-second
command:
cumulus@switch:~$ nv show platform pulse-per-second
applied
---------------------- -----------
in
state enabled
pin-index 0
channel-index 0
signal-width 500000000
signal-polarity rising-edge
timestamp-correction 0
logging-level info
out
state disabled
pin-index 1
channel-index 0
frequency-adjustment 1000000000
phase-adjustment 0
signal-width 500000000
To show only PPS In configuration settings, run the nv show platform pulse-per-second in
command:
cumulus@switch:~$ nv show platform pulse-per-second in
applied
-------------------- -----------
state enabled
pin-index 0
channel-index 0
signal-width 500000000
signal-polarity rising-edge
timestamp-correction 0
logging-level info
To show only PPS Out configuration settings, run the nv show platform pulse-per-second out
command:
cumulus@switch:~$ nv show platform pulse-per-second out
applied
-------------------- ----------
state disabled
pin-index 1
channel-index 0
frequency-adjustment 1000000000
phase-adjustment 0
signal-width 500000000