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configs for a boundary clock

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# Linux PTP Boundary Clock
In this case a server bridges the Raspberry Pi 5 grandmaster's RJ45 connection into the two QSFP+ links that feed NEXUS (the C93180LC-EX).
The physical PTP topology is:
```text
RPi5 Grandmaster
│
│ RJ45
\/
eno4
Linux boundary clock
│
├─ enp4s0 ── QSFP+ ──> NEXUS Eth1/5
└─ enp5s0d1 ─ QSFP+ ──> NEXUS Eth1/6
```
`eno4` is one of the servers's onboard RJ45 NICs. `enp4s0` and `enp5s0d1` are the two ports on the Mellanox ConnectX-3 Pro card.
It runs one multi-port `ptp4l` process as a real boundary clock. `phc2sys -a -r` follows the `ptp4l` port states and synchronizes the separate PHCs plus the Linux system clock.
## Files in this directory
| File | Install as | Purpose |
|---|---|---|
| `ptp4l-boundary.conf` | `/etc/linuxptp/ptp4l-boundary.conf` | Three-port boundary-clock configuration |
| `ptp4l-boundary.service` | `/etc/systemd/system/ptp4l-boundary.service` | Starts `ptp4l` on all three interfaces |
| `phc2sys-boundary.service` | `/etc/systemd/system/phc2sys-boundary.service` | Synchronizes the separate PHCs and `CLOCK_REALTIME` |
## 1. Install the required packages
```bash
sudo apt update
sudo apt install linuxptp ethtool
```
## 2. Verify interface names and hardware timestamping
The bundled configuration expects exactly these interfaces:
```text
eno4 upstream to RPi5
enp4s0 downstream to NEXUS
enp5s0d1 downstream to NEXUS
```
Verify them:
```bash
ip -br link show eno4 enp4s0 enp5s0d1
```
Check hardware timestamping on all three ports:
```bash
ethtool -T eno4
ethtool -T enp4s0
ethtool -T enp5s0d1
```
Each PTP port needs hardware TX/RX/raw timestamp support and a PHC.
Check which PHC belongs to each interface:
```bash
for i in eno4 enp4s0 enp5s0d1; do
echo "=== $i ==="
ethtool -T "$i" | grep -E 'PTP Hardware Clock|SOF_TIMESTAMPING_(TX|RX|RAW)_HARDWARE'
readlink -f /sys/class/net/"$i"/device/ptp/ptp* 2>/dev/null || true
done
```
The expected layout is normally:
```text
eno4 -> onboard NIC PHC
enp4s0 + enp5s0d1 -> Mellanox PHC
```
Because the upstream onboard NIC and Mellanox card use different PHCs, the configuration intentionally contains:
```text
boundary_clock_jbod 1
```
Do not remove it unless you have verified that every active `ptp4l` port is backed by the same PHC.
## 3. Install the boundary-clock files
From this directory:
```bash
sudo install -D -m 0644 ptp4l-boundary.conf /etc/linuxptp/ptp4l-boundary.conf
sudo install -D -m 0644 ptp4l-boundary.service /etc/systemd/system/ptp4l-boundary.service
sudo install -D -m 0644 phc2sys-boundary.service /etc/systemd/system/phc2sys-boundary.service
```
The PTP config is intentionally asymmetric:
```text
[eno4]
BMCA may select this as CLIENT/SLAVE to the RPi5
[enp4s0]
serverOnly 1
[enp5s0d1]
serverOnly 1
```
Both Mellanox links therefore advertise the server toward NEXUS, while only `eno4` can become the upstream client port.
## 4. Disable competing Linux clock synchronization
`phc2sys-boundary.service` uses `-r`, so the server's `CLOCK_REALTIME` is also disciplined from PTP. Do not leave chrony, ntpd, or systemd-timesyncd simultaneously controlling the system clock.
For example:
```bash
sudo systemctl disable --now chrony 2>/dev/null || true
sudo systemctl disable --now systemd-timesyncd 2>/dev/null || true
sudo systemctl disable --now ntp 2>/dev/null || true
sudo systemctl disable --now ntpd 2>/dev/null || true
```
## 5. Enable the services
```bash
sudo systemctl daemon-reload
sudo systemctl enable --now ptp4l-boundary.service
sudo systemctl enable --now phc2sys-boundary.service
```
The bundled `phc2sys` command is:
```bash
phc2sys -a -r -m
```
Here:
```text
-a follow ptp4l port states and automatically choose PHC source/sinks
-r also synchronize CLOCK_REALTIME as a sink
```
Use one `-r`, not `-rr`, for this design. System's system clock should not become an alternate PTP source.
## 6. Expected steady-state port roles
With the RPi5 grandmaster reachable on `eno4`, the server should converge to:
```text
eno4 CLIENT / SLAVE
enp4s0 SERVER / MASTER
enp5s0d1 SERVER / MASTER
```
The grandmaster identity should still be the RPi5 identity, and the server should report approximately:
```text
stepsRemoved = 1
```
The two Mellanox-facing ports are separate redundant paths toward the same Nexus. On NEXUS, one of those Nexus ports should become `Slave` and the other `Passive`.
## 7. Verification
Service state:
```bash
systemctl status ptp4l-boundary
systemctl status phc2sys-boundary
```
Live logs:
```bash
journalctl -fu ptp4l-boundary
journalctl -fu phc2sys-boundary
```
Query the PTP datasets:
```bash
sudo pmc -u -b 0 'GET PORT_DATA_SET'
sudo pmc -u -b 0 'GET CURRENT_DATA_SET'
sudo pmc -u -b 0 'GET PARENT_DATA_SET'
sudo pmc -u -b 0 'GET TIME_STATUS_NP'
```
Things to check:
```text
- eno4 has selected the RPi5 as its upstream master/server
- both Mellanox ports are master/server ports
- grandmasterIdentity is the RPi5 identity
- stepsRemoved is 1
- phc2sys offsets settle near zero
```
If you want to inspect each interface's PTP hardware again:
```bash
ethtool -T eno4
ethtool -T enp4s0
ethtool -T enp5s0d1
```
## 8. Failure behavior
The two NEXUS links are redundant from the Nexus BMCA perspective.
Normal state on NEXUS:
```text
one link Slave
other link Passive
```
If the selected link fails, the passive link should be eligible to become the new `Slave` port without changing the RPi5 grandmaster identity.
If `eno4` loses the RPi5 completely, the server no longer has its intended upstream reference. Investigate `ptp4l-boundary` and `phc2sys-boundary` before trusting time downstream.
## 9. Important filename/interface consistency
The actual second Mellanox interface is `enp5s0d1`. The `ptp4l-boundary.service` already uses that name, and the configuration in this bundle should also contain:
```text
[enp5s0d1]
serverOnly 1
```
If the OS renames any NIC after a hardware/firmware change, update both `ptp4l-boundary.conf` and `ptp4l-boundary.service` before restarting PTP.

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# /etc/systemd/system/phc2sys-boundary.service
[Unit]
Description=Synchronize PTP Boundary Clock PHCs
After=ptp4l-boundary.service
Requires=ptp4l-boundary.service
[Service]
Type=simple
ExecStart=/usr/sbin/phc2sys -a -r -m
Restart=always
RestartSec=3
[Install]
WantedBy=multi-user.target

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# /etc/linuxptp/ptp4l-boundary.conf
[global]
time_stamping hardware
domainNumber 0
network_transport UDPv4
delay_mechanism E2E
# Needed when the two NICs have different PHCs.
boundary_clock_jbod 1
# If both interfaces somehow share the same PHC, remove:
# boundary_clock_jbod 1
# We want the RPi GM to beat this clock in BMCA.
priority1 200
priority2 128
summary_interval 1
# Upstream toward RPi5.
# This is allowed to become the PTP client according to BMCA.
[eno4]
# Never accept another master from this direction.
# Downstream link 1 to Nexus
[enp4s0]
serverOnly 1
# Downstream link 2 to Nexus
[enp5s0d1]
serverOnly 1

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# /etc/systemd/system/ptp4l-boundary.service
[Unit]
Description=PTP Boundary Clock
After=network-online.target
Wants=network-online.target
[Service]
Type=simple
ExecStart=/usr/sbin/ptp4l \
-i eno4 \
-i enp4s0 \
-i enp5s0d1 \
-f /etc/linuxptp/ptp4l-boundary.conf \
-m
Restart=always
RestartSec=3
[Install]
WantedBy=multi-user.target