The build entrypoint invokes this application shell. The shell composes the existing Linux services, shared app catalog and LVGL UX pack. The SDL desktop port owns the window, touch and keyboard input. Board profiles contain display dimensions, orientation and fullscreen policy; the port contains no board IDs.

T-Display-CM0 selects t_display_p4_touch, including the P4 dashboard, menu, page layouts, on-screen keyboard and bottom-edge back gesture. Pages use the existing Linux platform services. The CM0 profile selects the LR2021 backend; other Linux compositions may retain SX126x or disable radio support. A shared coordinator restores mesh parameters after foreground RF tools release the chip. The Linux-only RadioLib dependency is pinned separately from ESP builds. Music uses the shared core player, rooted filesystem storage, SDL PCM output, volume and audio focus. Other audio workflows, GNSS and optional peripheral integration remain in progress; see docs/engineering/t-display-cm0-hardware-integration.md for the development ledger.

Build and run

CM0 cross builds must use C++ headers and a link library matching its Raspbian runtime, not generic Debian armhf defaults. See the target C++ ABI setup before building a deployable CM0 deb. Use a fresh build directory when changing the ABI.

On Linux install Python 3, CMake, Ninja, a C++20 compiler, libsdl2-dev (SDL >= 2.0.18), libcurl4-openssl-dev, libsqlite3-dev, libssl-dev, libjpeg-dev, libpng-dev, libarchive-dev, libfreetype6-dev, pkg-config and dpkg-dev. Phone Bluetooth is intentionally disabled and deferred; BlueZ and GIO are not required by the application.

cmake -S apps/linux_lvgl -B build/linux-lvgl -G Ninja \
  -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr \
  -DTRAIL_MATE_LINUX_DEVICE_CONFIG="$PWD/boards/t_display_cm0/package.cmake" \
  -DTRAIL_MATE_LINUX_DEB=ON
cmake --build build/linux-lvgl --parallel 4
ctest --test-dir build/linux-lvgl --output-on-failure
build/linux-lvgl/trailmate-linux --profile boards/t_display_cm0/device.conf

The application runs in the active X11 or Wayland desktop session. SDL selects the available backend; SDL_VIDEODRIVER=wayland or x11 can override it. Fullscreen is the device profile default. Alt+F4 and window-close requests end the loop and shut down application services. --windowed enables desktop development. --quit-after-ms 3000 --screenshot /tmp/trailmate.bmp provides a bounded capture; screenshots contain the unrotated logical UI.

The CM0 profile uses a 1232 x 568 landscape UI. The Raspberry Pi desktop already rotates DSI-1, so application rotation defaults to zero. Set rotation=90 in a copied profile for a session exposing the native 568 x 1232 portrait output. All four right-angle orientations are supported. Width, height, title, fullscreen and rotation belong to the profile, not shared code. The default hardware_keyboard=auto probes evdev key capabilities without consuming input. Explicit true/false overrides detection. With it disabled, touch editors keep the P4 on-screen keyboard; Alt+F4 still works. The profile's ux_pack must match TRAIL_MATE_LINUX_UX_PACK at build time; unlinked packs fail clearly instead of silently selecting another UI.

Debian package

cpack --config build/linux-lvgl/CPackConfig.cmake -G DEB
sudo apt install ./trailmate-cm0_*.deb

Build on the target OS/architecture or with a matching cross toolchain and sysroot. The vendor CM0 image is Raspberry Pi OS Trixie armhf; an amd64 desktop build is for testing and must not be installed on CM0. CPack derives native dependencies using dpkg-shlibdeps. The package installs its executable in /usr/bin, the profile in /usr/share/trailmate/devices, the desktop entry in /usr/share/applications, and the repository's existing images/logo.png in /usr/share/pixmaps. It does not install an autostart service or replace the vendor desktop/drivers.

To cross-build the CM0 armhf package from a Debian/Ubuntu amd64 host, install gcc-arm-linux-gnueabihf, g++-arm-linux-gnueabihf, curl, gnupg, dpkg-dev, cmake and ninja-build, then run:

bash apps/linux_lvgl/tools/build_cm0_deb.sh

The helper downloads signed Debian Trixie armhf development packages into an isolated sysroot and does not install foreign packages into the host. Its cache, output and parallelism can be set using TRAIL_MATE_PACKAGE_WORK, TRAIL_MATE_PACKAGE_OUT and TRAIL_MATE_PACKAGE_JOBS. Output defaults to build/cm0-deb. Cross-package runtime dependencies use Trixie's package names; native builds derive their dependencies with dpkg-shlibdeps.

For another Linux device, provide a new profile and desktop entry, and select its supported UX pack in the application composition. Keep peripheral drivers behind the existing Linux runtime ports.

Storage and sensor configuration

This desktop composition opts into XDG application paths: settings/state under $XDG_STATE_HOME/trailmate, user data under $XDG_DATA_HOME/trailmate, and cache under $XDG_CACHE_HOME/trailmate, with the usual $HOME fallbacks. The profile's optional absolute state_root, data_root, and cache_root override those defaults. Existing TRAIL_MATE_SETTINGS_ROOT, TRAIL_MATE_SD_ROOT, and TRAIL_MATE_CACHE_ROOT environment overrides take precedence. Legacy Linux compositions keep their previous locations until they explicitly opt in.

The music library uses the logical SD root and existing core Music/playlist formats. Audio targets SDL's default output rather than a board-specific ALSA card number. The application shuts down the player before SDL/LVGL teardown.

Native alerts use a worker and the same media volume/focus state as music. Saved speaker volume is restored before incoming messages are handled; zero mutes both music gain and alerts. A notification temporarily interrupts music and yields to an existing call/voice/RF audio owner. Capture uses a bounded one-second PCM ring and opens the default microphone only on explicit begin. SSTV uses this capture port and the shared receive core. Walkie uses native Codec2/WT v2 GFSK sessions with exclusive radio/audio ownership. Other voice/call integration remains incomplete.

IMU support uses standard Linux IIO accelerometer/gyroscope/temperature channels, including their scale and offset attributes. Configure imu_expected, imu_iio_root, optional imu_iio_device, imu_mount_rotation and orientation_policy in the device profile. sensor_landscape_only accepts debounced landscape flips and ignores portrait orientations. Missing or failed sensor channels remain not ready; no absolute compass heading is synthesized.

GNSS configuration uses gps_protocol=nmea|nordic_slm, optional absolute gps_device, gps_baud, gps_modem_lines and gps_gnss_only_setup. The CM0 baseline has no fitted GNSS/IMU expansion: it locks landscape orientation, does not expect an IMU, and does not claim a modem power line or issue SLM commands. Enable expansion settings only in a user-owned profile after fitting the hardware. A serial device can be an exact stable path or a filename pattern in one absolute directory, such as /dev/serial/by-id/usb-receiver_*-if00. A pattern must match exactly one character device; missing or ambiguous matches remain unavailable and are retried at the serial-open boundary. Directory patterns are unsupported, and each scan is bounded to 256 entries. With multiple matching receivers, configure the full by-id path or a dedicated udev alias. Existing TRAIL_MATE_GPS_DEVICE/NMEA-file overrides take precedence over the profile source; saved receiver-baud settings and environment overrides remain supported. Passive NMEA never sends AT commands. SLM is an explicit device choice and requires command acknowledgements before reporting ready. It projects #XGPS positions into the shared GPS service without fabricating satellites or HDOP. The GNSS-only setup flag disables cellular mode; keep it false for a modem whose LTE/GNSS coexistence is managed elsewhere. Disabling GPS requests a best-effort stop and releases the serial port.

Automatic display power control is an explicit profile capability: screen_power=wayland uses the compositor's wlopm interface, while the default screen_power=none leaves it unavailable. A single output is discovered automatically; with multiple outputs, set screen_power_output to its advertised name. The shared timeout, screen saver and sleep inhibitors run through the Linux screen service. Wake input is consumed before reaching pages or editors; SPACE confirms keyboard resume, and a subsequent upward swipe confirms touch resume. A lost output or failed power request releases the UI's sleep state. Shutdown attempts to restore outputs the application turned off. This does not provide brightness control. CM0 ships with automatic power cycling disabled pending physical confirmation of stock-panel recovery. See output power.

Wireless interface discovery accepts TRAIL_MATE_WIFI_INTERFACE as an explicit Linux interface name. Without it, exactly one wireless interface must be present; multiple adapters are unavailable until selected explicitly. The selection is validated against the wireless class marker, so a missing, renamed or wired interface does not silently fall back to another adapter. No wlan0 assumption is required. This selector affects the app's Wi-Fi controls; ordinary IP traffic continues to use the operating system's routes.

An explicit Wi-Fi enable or automatic connect request can try saved profiles in priority order on the worker. Existing desktop connections are retained. Manual connect/disconnect/disable and interface changes cancel the cycle; exhaustion stops app retries without disabling the system-wide NetworkManager radio. Merely saving profiles or starting the app does not initiate that cycle.

Brightness uses a background Linux backlight adapter. backlight_root defaults to /sys/class/backlight; optional backlight_device selects an absolute class device path. One valid device is auto-selected; multiple devices require explicit selection. Settings/quick controls use cached, normalized brightness and expose write failures rather than assuming success. Direct writes may fall back to logind for an active session. The stock CM0 kernel exposes no backlight class device. The experimental RM69A10 patch is not approved for deployment; retain the stock driver.

An opt-in backlight_backend=wayland_gamma uses compositor gamma tables for software display dimming. backlight_output selects a wl_output.name; an empty selection is accepted only when exactly one output exists. The connection uses WAYLAND_DISPLAY and XDG_RUNTIME_DIR, or an explicitly configured absolute backlight_socket. Multiple outputs never fall back to the first device. Exclusive-control rejection, output removal and compositor errors make the control unavailable. Shutdown disconnects the client, restoring the original gamma table according to the protocol. Cached levels describe accepted software attenuation, not measured optical output or panel hardware brightness. The default backend remains sysfs; the CM0 profile has not enabled gamma while physical confirmation is pending. Gamma does not enable output power cycling.

Protocol Probe uses a background Linux receive session. Configuration and TX completion govern dwell/response timers; generation tokens isolate retunes and prevent stale cleanup or packets from crossing candidates. Device I/O and lease release run on the worker, with bounded RX/TX storage. See foreground receive sessions.

Keyboard illumination has a separate optional PWM worker. Profiles configure keyboard_pwm_of_node, keyboard_pwm_channel, keyboard_pwm_period_ns, keyboard_pwm_max_duty_permille and keyboard_pwm_export. The controller is matched by its device-tree identity under /sys/firmware/devicetree/base, so a changing pwmchip number does not select another device. Multiple matches are unavailable rather than selecting the first. Test/custom systems may override keyboard_pwm_root and keyboard_pwm_device_tree_root explicitly.

The CM0 profile declares the software PWM node and a 100-permille full-scale duty limit, matching the vendor keyboard's on setting. Existing periods and levels are retained at startup. With export enabled, an uninitialized disabled channel receives the declared initial period; the app does not claim unrelated controllers. Requests and readback run in the worker, while UI getters return cached normalized levels. The shared menu advertises K to cycle keyboard illumination only while the runtime capability is available. Unconfigured profiles remain unavailable. This implementation uses ordinary sysfs access; it does not change the kernel, permissions or display brightness.

Radio protocol integration

Radio configuration and RX-start failures invalidate readiness and block packet I/O even if a backend retains its old online flag. Initialization failures use bounded nonblocking retry backoff rather than resetting hardware every UI tick. Explicit settings changes permit an immediate retry. This recovery policy does not itself make the underlying driver asynchronous. Application services now wrap the mesh engine in LinuxMeshWorker: configuration, crypto, receive polling and sends execute on one worker; UI callers enqueue bounded work and read cached state. Success from a send request means queue acceptance. Physical completion, delivery or failure updates the protocol-tagged message ledger separately. Metadata updates preserve queued receive data. Protocol/radio-context changes cancel old queued work; already-dispatched work reports its original protocol. Shutdown joins the owner and drains outcomes. Direct power-control and foreground probe call paths still require latency work.

The shared Linux radio adapter now supports MeshCore encrypted group text and group application data using enabled channel slots and the configured V1/V2 payload profile. It bounds receive/deduplication state and rejects wrong keys, corrupt data and UI-only channels. MeshCore identities are persisted independently from Meshtastic keys. Send ID Local/Broadcast send signed advertisements; verified incoming advertisements update contacts and valid advertised positions. A signed advertisement proves key possession, not manual verification of the peer. Scan Local sends tagged local discovery requests, collects matching responses for five seconds, and schedules bounded delayed replies to incoming requests. Its unsigned responses create provisional discoveries and do not establish trusted peer keys. Concurrent scans/ID announcements return Busy during receive collection; configuration changes cancel pending discovery work. Private text and application data use identity-derived shared secrets and require a peer key learned from a signed announcement. They currently send using flood fallback. Private text and requested app-data transport ACKs have bounded waiting and reply state; encrypted PATH ACKs match the expected peer/token, while legacy short ACKs require a unique pending token. Radio changes cancel stale work. MeshCore route/path learning, remaining control workflows, identity import/export and Reticulum remain incomplete; unsupported operations fail rather than sending the old TML1 frame. The current production GD binary envelope has no explicit length, so zero-ended application payloads are rejected to avoid silent loss. Peer interoperability has not been tested.

Reticulum IP calls can wait for verified public-key and telephony-path discovery when the target identity is known. The outgoing call remains cancellable while waiting, and its original link ID is retained when the route becomes available. The wait has a 30-second deadline; invalid signatures, mismatched identities, ignored peers, transport loss and cancellation do not send a handshake. Missing identity information still requires discovery before dialing. See call path waiting.

Walkie and device identity

Linux media can select SDL device names through TRAIL_MATE_AUDIO_INPUT_DEVICE and TRAIL_MATE_AUDIO_OUTPUT_DEVICE. The common output selection covers music, notifications and voice playback. A workflow's explicit capture selection takes precedence over the common input. Empty/unset selections follow the desktop's default route; an explicit unavailable selection fails to open instead of silently choosing another device. Run trailmate-linux-audio-probe --list-devices to inspect names exposed by the selected SDL backend without starting capture.

The media-enabled walkie backend uses Codec2 3200, WT v2 packets and GFSK through the foreground packet-radio port. Hold Space while the walkie page is active, or hold its touch PTT button. Release, focus loss and page exit stop PTT. The monitor setting keeps receive active after leaving the page; typing Space in another application does not start a transmission. Microphone selection uses TRAIL_MATE_WALKIE_INPUT_DEVICE, then TRAIL_MATE_AUDIO_INPUT_DEVICE, then the session default. Audio or radio failures are displayed from cached worker status; no synthetic levels are generated. Mesh traffic pauses during the session and resumes with its latest settings. Peer and physical audio validation remain pending.

Profiles select runtime_mode=mesh|local|demo; TRAIL_MATE_RUNTIME_MODE overrides the profile. CM0 ships in mesh mode. Production modes store an independent node ID in each device's SQLite state root. TRAIL_MATE_NODE_ID overrides the process base/Meshtastic ID using decimal or 0x notation without replacing that stored identity. MeshCore uses its own persistent public-key-derived ID. On upgrading an old installation that used the fixed ID, peers may need rediscovery or re-pairing. Explicitly pin an old ID only when it is unique on the network. Settings, history and existing key tables are retained.

SSTV reception

The media-enabled build uses native microphone PCM at 15 kHz and the portable core_sstv DSP. Receive/stop actions are asynchronous. Capture holds SSTV audio focus to interrupt music, handles bounded input overruns by reacquiring sync, and publishes coherent preview copies to the shared page. Silence does not generate an image. A completed image is saved as a uniquely named BMP under the SD data root's sstv directory; TRAIL_MATE_SSTV_OUTPUT_DIR overrides it. Saving and decoding never run in an LVGL callback.

TRAIL_MATE_SSTV_INPUT_DEVICE optionally selects an SDL input device; otherwise the common input selection or session default is used. For explicit offline PCM input, TRAIL_MATE_SSTV_PCM_FILE reads signed little-endian 16-bit mono samples at exactly 15000 Hz. This is not a WAV parser. Missing/truncated/incomplete inputs report errors rather than generating a completed image. The inherited DSP acquires modes from scan-sync cadence, not VIS. Acquisition can omit initial lines even when the input contains a header. First-row alignment and full on-air/multi-mode validation remain pending.

The non-installed trailmate-linux-sstv-probe INPUT_PCM OUTPUT_DIRECTORY build tool runs this exact decoder/persistence path with explicit offline input and a bounded wait. It is useful for comparing native/target results without opening an input device. The BW8 test fixture produced identical BMP bytes on the host and CM0 ARM CPU.

Bounded native audio probe

Media builds also provide the non-installed trailmate-linux-audio-probe tool:

./trailmate-linux-audio-probe --capture-ms 1000 --rate 15000 --play-silence

The explicit capture duration must be 100-5000 ms and the rate 8000-48000 Hz. Use --input NAME to select an SDL capture device instead of the desktop default. The probe reports sample counts, nonzero sample counts, peak amplitude, dropped samples and whether capture stopped cleanly. It never saves or transmits a recording. --play-silence additionally opens playback, queues 100 ms of digital silence, drains the queue and closes the device. Transport success does not prove physical microphone input or audible speaker output. All-zero capture may require checking mute, codec routing, input wiring and the connected microphone rather than assuming that device enumeration proves readiness. A dummy-audio CTest exercises the bounded lifecycle on the host.

Native Reticulum status

Selecting Reticulum now initializes a separate persistent X25519/Ed25519 identity on the mesh worker. Public identity/address information is read from a cached snapshot; damaged identity storage is reported without generating a replacement. Incoming announcements now pass the shared signature/destination verifier and existing path manager, with copied RX counters in diagnostics. Paths remain transient and do not grant contact trust. Directory path requests can be queued through the mesh port with TX permission, cooldown and expiry checks. Verified person announcements now enter the shared identity registry and thread-safe native peer directory; service announcements do not become contacts. Local trust/ignore/favorite/alias policy is preserved. The shared link owner now handles handshake/control packets. Signed plain text within a link's packet-size limit reaches the existing chat service and SQLite store; its packet proof is sent only after durable application acceptance. Bad signatures, ignored sources and unsupported payloads are not acknowledged as text. Plain peer-text sending now discovers paths/keys, establishes links and reports Sent only after complete radio submission, then Delivered only after a matching signed packet proof or validated resource completion proof. Larger peer-text envelopes use encrypted unsplit resources, optionally compressed with bzip2; incoming confirmation still waits for durable storage. Split resources, metadata, group/opportunistic messages, custom/application fields, propagation and dependent network workflows remain unavailable. See Linux Reticulum integration.

Native Geocaching status

Local drafts and authenticated recovered offline copies feed the shared Map overlay through bounded asynchronous windows. Saved position/name changes, archival and local deletion refresh a stationary Map; archived drafts and unknown coordinates are excluded. Local drafts remain usable when offline storage is missing, and the browse page retains its storage error. Directory discovery, live download and signed publication still require the native Reticulum/LXMF transport and remaining business composition. See Linux geocaching integration.

Native Agenda status

The Linux Agenda store, clock and background source are available for composition. They reuse the core record encoding, stable IDs, recurrence and reminder rules, and the clock follows product/system timezone settings with suspend-aware monotonic time. The worker publishes sealed read projections and drains accepted commands on shutdown. The entry point creates the service and supplies Calendar to the shared catalog, page/Map flow, dashboard and reminder popup. Popups defer while audio focus is busy. A separate native worker persists saved waypoints in the same configured database and supplies the shared location picker. Saving a location as a waypoint waits for a durable commit; selection uses bounded pagination over a sealed read projection without SQLite work on the UI thread. See Linux Agenda integration.

VMP audio backend status

Media builds include a worker-owned NativeVoiceAudio adapter matching the production Codec2-1300 voice profile: 8 kHz mono, at most five seconds and 875 encoded bytes. It supports early stop, cancellation, bounded playback, volume and exclusive audio focus. A SQLite attachment port now persists the shared eight-entry inbox, including stable local IDs, read/delivery state and safe restoration of interrupted sends. Application services now own the voice worker and bind the shared chat voice interface on compatible media/radio compositions. A passing codec/PCM test does not establish a working physical microphone or a complete voice-message send.

The direct-RF port now supports VMP profile 1 through a foreground radio lease and isolates VMP control envelopes before generic mesh parsing. Backend-specific capability checks keep SX126x constraints separate from the LR2021 media PHY. Checked release reports a failed normal-radio restoration rather than silently claiming success. A worker-owned session executor now implements broadcast and verified-contact private handshakes, authenticated media/FEC recovery, bounded waits and cancellation. Private ACCEPT replies require a durable one-time reservation, preserving nonce-use history independently of retained messages. The reservation journal must not be erased or rolled back while retaining the same contact-key schedule. The bounded application mailbox and UI binding now connect public record/send, incoming attachments, playback and read state. Storage and RF work remain on the voice/mesh workers; protocol switches cancel old-context jobs. An injected mesh radio requires its matching foreground port. The verified-contact provider now derives VMP-only keys from the existing MT/MC identities and manually verified public directory pins. Public keys travel from the mesh worker's cached snapshot into that directory; discovery never grants manual verification. Trust changes cancel old jobs, and derivation racing a revocation is discarded. MT and MC number/code verification are connected to the shared UI. MC uses authenticated V1/V2 direct controls and its existing identity shared secret; user comparison acceptance grants the directory pin. The shared fixed-control padding decoder preserves zero bytes at the end of the nonce. Unverified private requests continue to fail closed. The real CM0 capture probe still returns only zero samples; physical microphone/speaker and peer RF validation remain unproven.

The RX-only trailmate-linux-radio-probe build tool accepts --vmp-channel 0..39 to configure this media profile temporarily, then restores LoRa before releasing the radio. Supply the SPI/GPIO/TCXO arguments from the target profile. This probe never transmits; configuration success does not establish peer interoperability.

External resource storage

The Linux composition reads installed language, font and IME resources from <resolved data root>/trailmate/packs. TRAIL_MATE_RESOURCE_PACK_ROOT overrides this complete resource directory. The local package catalog defaults to <resolved data root>/pack-catalog, with TRAIL_MATE_PACK_ROOT as its override. Catalog entries and installed resources are distinct. Local directory packages install real resources and installed records through atomic snapshots. Shared resources are retained while another installed package owns them; conflicting contents reject the operation. Minimum firmware versions and supported memory profiles are evaluated for listing and rechecked against the staged manifest before publication. The runtime build version follows the same CI tag/Changelog source as firmware builds; package versions default to its Debian form. Explicit package-version overrides remain available. Remote catalog/archive delivery remains incomplete. See resource storage.

Native Linux LVGL builds also scan /usr/share/trailmate/packs when installed with the /usr prefix. The optional trailmate-linux-fonts package supplies full CJK fonts, compact color emoji and released display-language tables. User resources take precedence. See the Linux font package for installation, coverage, input-method ownership and validation.

Phone Bluetooth scope

Phone Bluetooth is intentionally disabled for the current Linux release, including T-Display-CM0 and Cardputer Zero. Legacy configuration and composition flags cannot start the phone service. The retained transport and session code is deferred development material, not a supported application feature. Pairing, phone administration and Bluetooth interoperability are outside this delivery. The application does not require BlueZ or GIO; no further Bluetooth controller or boot configuration changes are part of this work. Application restart requests now release run-owned services before re-executing with the original arguments; window close and Alt+F4 take priority. Clock writes use the operating-system interface and report authorization failures. See the runtime integration record for the remaining implementation and verification scope.