T383838grl is the Go Reticulum Lifesaver: a sovereign, pocket-sized off-grid

survival communicator and field assistant in one executable.

The same application is designed to run on an ultra-low-power ESP32-C5 as

bare-metal firmware and, unchanged in behaviour, on a workstation. T383838grl is the

workstation half of that promise, and it is the reference the firmware is

measured against. There is no second implementation to drift out of sync: the

field tools, the sensors, and the dashboard are one library

(github.com/gmlewis/go-reticulum/bot)

that both the appliance

and the RRC chat bot run.

!!! info "The Golden Architecture Rule"

**Survival intelligence runs locally, in-process, with zero radio hops and

zero airtime.** A first-aid card, a repeater bearing, the sunset, or the

position card must resolve in microseconds, in RAM, whether or not a single

packet can be sent. Long-range radio is reserved for what radio is for:

distress beacons, coordinating with rescue teams, peer messaging, and syncing

with a hub only when a gateway happens to be reachable.

!!! danger "Important Safety, Emergency & Medical Notice"

GRL is NOT a certified life-safety device, distress beacon, or medical device. Transmissions occur over best-effort unlicensed radio frequencies with NO guarantee of packet delivery, acknowledgement, or rescue. This system is NOT connected to official 911/112 dispatch, civil defense agencies, or search-and-rescue satellites. Under no circumstances should this system be used as a primary or sole means of summoning emergency rescue or medical assistance. Always carry certified primary safety equipment (EPIRB/PLB, paper maps, magnetic compass). Read the full Legal, Safety, Emergency, and Medical Disclaimer below before building or operating this device.

One T383838grl process brings up four things, in this order:

203

| Subsystem | What it is | When it runs |

|---|---|---|

| Reticulum | A local RNS stack, configured by T383838rns.config_path | Always |

| Sensors | A pure-Go NMEA-0183 GNSS receiver and electronic compass, or their static fallbacks | When a port or a static value is configured |

| Field assistant | The shared in-process command engine (T383838bot.Engine): T383838whereami, T383838med, T383838tower, T383838sun, T383838moon, T383838sos, T383838checkin, T383838morse, T383838conv, T383838firstaid, and the rest | Always |

| Captive dashboard | An HTTP dashboard and JSON API for a smartphone browser | When T383838portal_addr is set |

Shutdown is the reverse, so nothing is left reading a device or holding a

socket. T383838grl exits 0 on a clean exit, 1 on an operational failure, and

2 on a usage error.

Commercial satellite messengers cost $300–$600 and charge $15–$65 per month; if

the subscription lapses, the emergency hardware is remotely deactivated.

They also cannot tell you what to do about hypothermia, cannot find the nearest

amateur repeater, and cannot function without a satellite link.

T383838grl inverts all three properties:

• No subscription, no account, no app store. The knowledge is compiled in.

• No vendor silo. It speaks Reticulum, so it talks to any Reticulum peer,

any RRC hub, any LXMF destination, and any amateur operator running the same

open stack.

• No link required for the answers that matter. The survival tools are pure

mathematics and embedded static tables, so a canyon, a wet tree canopy, or a

ridgeline between you and the nearest relay changes nothing about the first-aid

card or the position card.

Sourcing a custom LCD, a physical keyboard, and an injection-moulded case is

what drives open communicators to $80–$150 and produces fragile gadgets with

tiny keys. Almost every traveller already carries a better terminal: a phone

with a high-resolution touchscreen and a modern browser, whose Wi-Fi and browser

keep working in airplane mode with zero cellular coverage.

So T383838grl serves the dashboard over HTTP and lets the phone be the screen:

• On the ESP32-C5 target, the appliance brings up a Wi-Fi 6 SoftAP

(T383838Reticulum-Lifesaver-[ID]); the phone joins it and its operating system pops

the dashboard up by itself.

• On a desktop workstation, T383838grl hosts the same dashboard on

T383838portal_addr with no root privileges and without touching the host's Wi-Fi

adapters. Open <http://localhost:9111/> in any browser — including the one on

the phone next to you, when you bind T3838380.0.0.0:9111.

Either way the URL routing is identical, because every captive-probe route the

common operating systems already request answers with T383838302 Found → /:

| Probe route | Requested by |

|---|---|

| T383838/generate_204, T383838/gen_204 | Android |

| T383838/hotspot-detect.html | Apple iOS and macOS |

| T383838/ncsi.txt, T383838/connecttest.txt | Windows |

195

| Card | What it shows |

|---|---|

| Where Am I | Plus Code (with a copy button), coordinates, Maidenhead grid, elevation, GNSS fix quality, local solar time, and the sunset countdown |

| Compass & Direction Finding | A live compass rose with a second needle vectored at the nearest repeater, cell site, or active distress beacon, and the relative turn that aims an antenna at it |

| Emergency | A single-button SOS that raises a distress beacon at the verified position |

| Field Assistant | A query box that runs the same offline commands the radio answers, with zero hops |

The dashboard is a client of its own API, so a widget, a second screen, or a

script can poll the same facts:

191

| Method | Path | Answer |

|---|---|---|

| T383838GET | T383838/api/whereami | The operational card as JSON, including T383838plus_code, T383838coordinates, T383838maidenhead, T383838sunset_countdown, T383838lines (the card exactly as the radio renders it), and a live T383838heading |

| T383838GET | T383838/api/compass | The live heading: magnetic, true, the local variation, the cardinal sector, and the nearest site or beacon |

| T383838POST | T383838/api/query | Runs one offline command. Body: T383838{"command": "med hypothermia"} (or T383838{"text": "..."}) |

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T383838grl writes a fully commented T383838~/.grl/config.toml on the first run and keeps

running — it needs no editing to be useful. Open

<http://localhost:9111/> and the dashboard is live.

With no hardware attached at all, the appliance still works: set a

T383838static_fix and a T383838static_heading and every position-aware tool answers from

them. That is how the same configuration serves a desk and a trail.

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To see exactly which file and which devices an appliance resolved:

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125

| Flag | Meaning |

|---|---|

| T383838-config PATH | Configuration file to use. Default: T383838$GRL_HOME/config.toml, or T383838~/.grl/config.toml |

| T383838-portal-addr ADDR | Dashboard listen address, like T383838127.0.0.1:9111 or T3838380.0.0.0:9111. An empty value disables the dashboard |

| T383838-gps-port PORT | GNSS receiver serial port, like T383838/dev/tty.usbserial-0001 or T383838/dev/ttyUSB0 |

| T383838-compass-port PORT | Electronic compass serial port, like T383838/dev/tty.usbserial-0002 or T383838/dev/ttyUSB1 |

| T383838-quiet | Only report errors |

| T383838-verbose | Print the resolved configuration and run the Reticulum log at INFO |

| T383838-version, T383838-V | Print the version and exit |

| T383838-h, T383838-help | Print the usage text and exit |

Every flag is an override: a flag that is not given leaves the

configuration file's value alone, and an override is validated with exactly the

same wording as a bad file, so a typo on the command line is reported before

anything binds.

T383838GRL_HOME overrides the appliance's home directory (used literally, with no

expansion). It is how a second appliance — or a test — stays isolated on one

workstation.

T383838~/.grl/config.toml is a TOML document. Every value below is the built-in

default, and the file T383838grl generates is those defaults, with comments. A

configuration with no file at all still runs.

A leading T383838~ expands to your home directory in T383838storage_dir,

T383838rns.config_path, T383838gnss.port, and T383838compass.port.

152

| Key | Default | Meaning |

|---|---|---|

| T383838callsign | T383838"GRL-NOMAD" | The name the appliance answers to on the mesh. The default is deliberately fictional — replace it before transmitting |

| T383838nickname | T383838"" | An optional shorter name used on the air. Empty means "use the callsign" |

| T383838storage_dir | T383838~/.grl/storage | Where the appliance keeps distress beacons, situation reports, check-in timers, and saved history |

118

| Key | Default | Meaning |

|---|---|---|

| T383838portal_addr | T383838"127.0.0.1:9111" | The dashboard's listen address. Empty disables it entirely — no listener is bound |

188

| Value | Effect |

|---|---|

| T383838127.0.0.1:9111 | Desktop testing mode. Reachable only from this workstation, at <http://localhost:9111/>. Nothing is exposed to the local network |

| T3838380.0.0.0:9111 | Field / LAN mode. Reachable from every device on the same network at T383838http://<this-host>:9111/. Use this to test the real smartphone experience before you have hardware |

| T383838:9111 | Reachable on every interface and address family |

| (empty) | No dashboard at all. The field assistant is still complete and still answers |

162

| Key | Default | Meaning |

|---|---|---|

| T383838port | T383838"" | The NMEA-0183 receiver device, e.g. T383838/dev/tty.usbserial-0001 (macOS) or T383838/dev/ttyUSB0 (Linux) |

| T383838baud | T3838389600 | The receiver's line speed. See the note below |

| T383838static_fix | T383838"" | A fixed position in any notation T383838whereami accepts, e.g. T383838"37.7553,-122.4527". Used when no receiver is attached (or when no port is set) |

!!! note "Line speed"

The shared NMEA reader opens the device **read-only without reconfiguring

its line speed**, because changing it requires platform-specific termios

ioctls that the standard library does not expose. A fresh USB-UART adapter

is conventionally already at 9600, which is the default here. If your

receiver needs another speed, set it on the device (`stty -f /dev/ttyUSB0

38400T383838) or rely on the receiver's own auto-baud. baud` records the intended

hardware profile, and is the value the ESP32-C5 firmware's UART setup uses,

so one configuration describes both targets.

112

| Key | Default | Meaning |

|---|---|---|

| T383838port | T383838"" | The NMEA-0183 compass device, e.g. T383838/dev/tty.usbserial-0002 or T383838/dev/ttyUSB1 |

| T383838baud | T3838389600 | The compass's line speed (same note as above) |

| T383838static_heading | T383838"" | A fixed magnetic heading in degrees, e.g. T383838"042". Used when no compass is attached |

A magnetic heading is converted to true north with the World Magnetic Model

at the device's own position, so the dashboard and the field tools never

disagree about which way you are facing.

134

| Key | Default | Meaning |

|---|---|---|

| T383838config_path | T383838"" | The Reticulum configuration directory this appliance uses. Empty means the Reticulum default, T383838~/.reticulum |

151

| Key | Default | Meaning |

|---|---|---|

| T383838rooms | T383838["general", "emergency"] | The RRC rooms this appliance joins when a hub is reachable, and serves from its own local broker when one is not |

Both peripherals are ordinary USB-UART serial adapters. No driver, no

library, no Cgo: T383838grl reads NMEA-0183 ASCII sentences directly.

| Platform | Typical device names |

|---|---|

| macOS | T383838/dev/tty.usbserial-*, T383838/dev/tty.usbmodem-*, T383838/dev/cu.usbserial-* |

| Linux Mint / Ubuntu | T383838/dev/ttyUSB*, T383838/dev/ttyACM* |

Find yours by listing the device nodes before and after plugging the adapter in:

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Then name them in the configuration:

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Notes for the bench:

• T383838static_fix and T383838static_heading remain in the file while a port is set.

The port wins, so unplugging the receiver degrades to the last known position

instead of to nothing.

• On macOS prefer the callout device (T383838/dev/cu.usbserial-*) if the callin

device (T383838/dev/tty.usbserial-*) reports T383838EBUSY with nothing holding it — the

callin device waits on the modem-control lock.

• Permissions: on Linux, add yourself to the T383838dialout group (then log back in)

rather than running T383838grl as root.

• Both peripherals are optional and independent. A receiver with no compass

gives the position card; a compass with no receiver gives the heading, since a

compass works standing still and a receiver that has not locked does not.

• The reader expects the conventional 9600 8N1 NMEA stream: T383838$GNRMC/

T383838$GNGGA for position and T383838$HCHDG/T383838$HCHDM for heading.

1. The appliance sits in a pocket or carabiner-clipped to a pack, listening.

2. The traveller opens Wi-Fi settings and taps T383838Reticulum-Lifesaver-[ID].

3. The phone's captive-portal probe is answered with a redirect, so the

dashboard pops up by itself — no app, no store, no account.

4. The traveller reads the Plus Code aloud to a rescue team, steers an antenna

at the nearest repeater, or asks the assistant T383838med snakebite.

5. The phone goes back in the pocket; the appliance keeps listening, caching

what arrives.

To rehearse step 2–3 before you have hardware, bind T3838380.0.0.0:9111 on a laptop

and open T383838http://<laptop-ip>:9111/ from the phone.

T383838grl contains almost no survival logic of its own. Everything it answers with

lives in github.com/gmlewis/go-reticulum/bot, which is also

what T383838gorrcbot runs — so the radio reply and the dashboard answer can never

drift apart:

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T383838grl's own code is only the parts that are specific to being an appliance:

| File | What it does |

|---|---|

| T383838main.go | Flags, configuration loading and overrides, signal handling, exit codes |

| T383838flags.go | The CLI contract: T383838usageText and a package-local parser |

| T383838config.go | T383838~/.grl/config.toml: parsing, defaults, validation, T383838~ expansion |

| T383838app.go | The lifecycle: Reticulum → sensors → engine → dashboard, and back down |

Because T383838bot.Engine opens no socket and starts no goroutine, an appliance whose

dashboard is switched off still has a complete offline field assistant

available to any caller, and an appliance whose radio cannot start is reported

rather than silently downgraded.

153

| Symptom | Cause and fix |

|---|---|

| T383838could not start Reticulum | T383838rns.config_path names a directory Reticulum cannot use. An empty value means T383838~/.reticulum |

| Dashboard unreachable from a phone | T383838portal_addr is still T383838127.0.0.1:9111 (this workstation only). Set T3838380.0.0.0:9111 |

| T383838listen ... address already in use | Another process holds the port (often a previous T383838grl). Change T383838portal_addr, or find the holder with T383838lsof -i :9111 |

| T383838whereami says no fix | No receiver is attached and no T383838static_fix is set. Set one, or check the port and permissions |

| Heading is magnetic-only | A compass is attached but there is no position, so the WMM correction has nothing to work from. Set a fix |

| T383838portal.portal_addr: want host:port | A typo such as T383838localhost or T383838127.0.0.1 with no port. Use T383838host:port |

• The configuration file is created mode T3838380600 and is never rewritten once

it exists, so an operator's edits are the only source of truth.

• The default T383838portal_addr binds the loopback interface only. Nothing about

your position or heading is exposed to the local network until you deliberately

choose T3838380.0.0.0 or a specific interface.

• The dashboard is a read-mostly local surface: it runs only the commands

that compute their answer in-process. A command that needs a live hub link

says so rather than failing.

• The appliance holds its own cryptographic identity via Reticulum; there is no

account, no telemetry, and no vendor service in the path.

--8<-- "DISCLAIMER.md:3"

• gorrcbot — the same engine as an always-on RRC chat bot

• gobot — one-shot CLI for asking a live bot a single question

• GRL Hardware Project Plans — full GRL puck architecture, BOM table, and ESP32-C5 pinout

• Hardware guides — LoRa RNodes, carrier boards, and serial adapters

• ASIC Plans §6.9–§6.12

— the full GRL design, BOM, and pinout