3. Host platform (Raspberry Pi 5)
BigFred runs on the Pi as loco-server (HTTP + control-plane WebSocket),
dcc-bus (throttle data plane — LocoNet serial or Z21 UDP), Redis, and
process supervision ( supervisord on Raspberry Pi OS, BusyBox S* scripts
on the reference hub image — §8).
The host must keep up with USB serial or UDP Z21 traffic and SQLite writes without multi-second stalls.
3.1 Bill of materials
| Item | Recommendation |
|---|---|
| Raspberry Pi 5 | 8 GB RAM (4 GB minimum for one layout + one dcc-bus) |
| Raspberry Pi 5 M.2 HAT+ | Official M.2 HAT+ for Pi 5 (NVMe) |
| NVMe SSD | See §8.4 — e.g. WD SN740 256 GB |
| Rescue microSD | Endurance 32 GB (Samsung PRO Endurance, SanDisk Max Endurance) — optional |
| Power supply | Official 27 W USB-C PSU for Pi 5 |
| Cooling | Active cooler; fanctl on reference image (§8.8) |
| Ethernet | Gigabit cable to club LAN (preferred over WiFi for many clients) |
| Uhlenbrock 63120 | DR5000 path only — art. 63120 + LocoNet-Tool for LNCV |
| LocoNet cable | 6P6C RJ12 to DR5000 LocoNet-T |
| USB cable | Pi ↔ Uhlenbrock 63120 (DR5000 path only) |
RB1110 / RB1110-Mini: same Pi and NVMe; no Uhlenbrock 63120 — §7.
Optional (DR5000 LocoNet): Uhlenbrock 62280 (Luisa) (§2).
3.2 Operating system choice
| Image | When to use | Documentation |
|---|---|---|
| Hub OS (Buildroot) | Production club hub | §8 Hub OS image |
| Raspberry Pi OS 64-bit | Development, interim bring-up | This section (§3.3–§3.6) |
The reference production image provides PREEMPT_RT, read-only root,
/data on NVMe, CPU isolation, and make image automation. Raspberry
Pi OS is acceptable for testing BigFred before the Buildroot image is flashed.
Raspberry Pi OS on NVMe (interim)
Install Raspberry Pi OS (64-bit) with root on NVMe via the imaging tool. Keep microSD only for firmware rescue if needed.
Why latency matters
| Workload | Sensitive to slow disk? |
|---|---|
| SQLite | Yes |
| Logs | Moderate |
| Redis | Low (persistence under /data on hub image) |
| LocoNet / Z21 I/O | No (not disk-bound per packet) |
On Pi OS, use NVMe root (not SD daily driver). On the hub image, SQLite and
Redis live on /data (§8.4).
Pi OS fstab tuning (RW root)
UUID=... / ext4 noatime,nodiratime,commit=1 0 1Disable swap or use zram only on 8 GB boards.
3.3 PREEMPT_RT Linux kernel
Goal: reduce scheduling jitter for dcc-bus (USB or UDP).
| Deployment | RT kernel |
|---|---|
| Hub OS image | Built with CONFIG_PREEMPT_RT — §8.6 |
| Raspberry Pi OS | Install packaged RT kernel if available, else latest kernel + sysctl below |
Pi OS fallback:
# /etc/sysctl.d/99-bigfred-latency.conf
kernel.sched_rt_runtime_us = -1
vm.swappiness = 10echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governorOn the hub image, isolcpus / taskset in §8.6 replace optional systemd
nice/IO tuning.
3.4 USB and serial stability (DR5000 path)
| Practice | Reason |
|---|---|
| Uhlenbrock 63120 on USB 3 | Bandwidth |
| Short USB cable | EMI / voltage |
| udev stable symlink | §3.5 |
User in dialout |
Serial permissions |
Single opener of /dev/loconet-63120 |
No minicom while dcc-bus runs |
3.5 udev rule for Uhlenbrock 63120
udevadm info -a -n /dev/ttyACM0 | grep -E '{idVendor}|{idProduct}|{serial}'# /etc/udev/rules.d/99-uhlenbrock-63120.rules
SUBSYSTEM=="tty", ATTRS{idVendor}=="xxxx", ATTRS{idProduct}=="yyyy", SYMLINK+="loconet-63120", GROUP="dialout", MODE="0660"On the hub image, bake this rule into the Buildroot overlay (§8.9).
3.6 Build and deploy BigFred
Cross-compile (both images)
CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -o bin/loco-server ./pkgs/bigfred/serverInstall paths:
| Image | Binaries | Web UI |
|---|---|---|
| Hub OS | /usr/bin/ via Buildroot package |
/usr/share/bigfred/web (overlay) |
| Pi OS | bin/ + supervisord |
web/dist per 15-supervisord |
Production flash procedure: §8.10. Log rotation: §8.9.
Continue with §4 Uhlenbrock 63120 or §8 Hub OS.