Shareframe (Hardware)

Shareframe-Board is the custom embedded Linux operating system that runs on the Shareframe e-paper picture frames. It is a Buildroot-built firmware image for the Raspberry Pi Zero W with a read-only squashfs root filesystem, s6 as PID 1, and signed A/B over-the-air updates via RAUC on top of the Raspberry Pi tryboot mechanism. At runtime the board connects to the Shareframe web server over a WebSocket, receives the photos shared to it, and renders them on the e-paper panel as a slideshow.

Related repos

• shareframe-board — C++ application firmware and local web dashboard of the picture frame Raspberry Pi Zero hardware board
• shareframe — web application platform: server backend and web frontend

Highlights

• Read-only squashfs root filesystem with a separate writable f2fs /data for per-device persisted state and secrets
• s6 supervised services with ordered startup
• Signed A/B over-the-air updates (RAUC + tryboot) with automatic rollback on a failed slot
• USB-gadget networking for development plus WiFi with a STA → AP fallback so the board is always reachable
• Local management dashboard served on the board itself, discoverable at shareframe-board.local

Project

Figure 1: Front view of the picture frame

Figure 2: Back view of the picture frame

Architecture

Figure 3: Outline of the on-device architecture of the Shareframe-Board firmware

Base system:

• Buildroot: Builds the complete SD card image from source — kernel, root filesystem, and all packages below.
• s6-linux-init + s6-rc: Runs as PID 1 and supervises every service, bringing the service groups up in a defined order and restarting them on failure.

Hardware I/O:

• usb0: USB gadget (dwc2) interface used for ethernet-over-USB and serial access during development.
• wlan0: Onboard BCM43438 WiFi, the board's primary network link in normal operation.
• UART ttyS1: Serial console for low-level debugging.
• SPI0: Bus driving the e-paper panel.
• ACT LED: Surfaces boot and status codes via the activity LED.

Networking:

• wifi-mode-manager: Owns wlan0 and switches it between station (STA) and access-point (AP) mode.
• wpa_supplicant + dhcpcd: Default STA mode — connects to the configured home WiFi network.
• hostapd + dnsmasq: AP fallback — opens a setup access point when no configured network is reachable.
• setup-usb0 + udhcpd: Brings up the USB network; the board (10.55.0.1) hands a .2 address to any connected device.

System services:

• nginx :80: Serves the local board management dashboard and proxies its requests.
• dropbear: Lightweight SSH server for remote access.
• avahi: mDNS hostname resolution on the local network (shareframe-board.local).
• ntpd, watchdog, earlyoom, crond, getty, …: Supporting system daemons — time sync, hardware watchdog, out-of-memory protection, scheduled jobs, and console login.

Application (shareframe-board):

• shareframe-dashboard: Local web UI for configuring and managing the frame.
• shareframe-websocket: Maintains the persistent WebSocket link to the Shareframe web server and receives shared photos.
• shareframe-display: Drives the e-paper panel slideshow over SPI.
• shareframe-update: Pulls and applies signed update bundles.
• shareframe-heartbeat: Periodically reports the frame's liveness and status to the server.

Updates & health:

• RAUC + tryboot-backend: Performs signed A/B partition updates, writing the new firmware to the inactive slot and switching the active slot via tryboot.
• rauc-mark-good: Commits the new slot once it boots and validates successfully; otherwise the board automatically rolls back to the previous slot.
• shareframe-health: Ongoing system health checks (memory, temperature, disk, crashes).

Storage (SD card):

• p1 — FAT boot: Raspberry Pi firmware, A/B os_prefix directories, and config.txt / tryboot.txt.
• p2 / p3 — squashfs rootfs A/B: The two read-only root filesystem slots used by A/B updates.
• p4 — f2fs /data: Writable partition holding per-device state and secrets.