LoRa Region → Preset Compatibility

For 2.8 the firmware reworked LoRa regions and modem presets so that not every preset is legal in every region — the EU SRD / narrow bands, the amateur (ham) bands, and the 2.4 GHz band each accept only a subset. The firmware enforces this internally, but a client had no way to know the rules, so a user could pick an illegal region+preset pair and only discover it after the radio silently corrected it.

The radio now declares the legal region→preset combinations to the client during the want_config handshake, so the LoRa config screen can constrain the preset picker to the valid set for the selected region (and warn about licensed-only bands). It is advisory metadata — the firmware remains the source of truth and still validates/clamps on its own.

Protocol

Three messages in mesh.proto plus one new FromRadio oneof variant (field 19), generated into MeshtasticProtobufs:

message LoRaPresetGroup {
  repeated Config.LoRaConfig.ModemPreset presets = 1;       // legal presets for this group
  Config.LoRaConfig.ModemPreset         default_preset = 2; // always one of `presets`
  bool                                  licensed_only = 3;  // ham/amateur band → warn/gate
}
message LoRaRegionPresets {
  Config.LoRaConfig.RegionCode region = 1;
  uint32                       group_index = 2; // index into LoRaRegionPresetMap.groups
}
message LoRaRegionPresetMap {
  repeated LoRaPresetGroup    groups = 1;        // each distinct preset list, once
  repeated LoRaRegionPresets  region_groups = 2; // every known region → a group index
}

The map is delivered grouped (each distinct preset list appears once in groups; region_groups maps every region to a group by index) so it fits in a single 512-byte FromRadio packet. It arrives once, immediately after metadata and before the first channel, on a full or config-only want_config. It is omitted by the nodes-only nonce and by firmware older than 2.8.

Decode and storage

The grouped wire form is flattened into a per-region lookup by LoRaRegionPresetMap.decoded() in LoraConfigEnums.swift:

struct RegionPresetInfo: Equatable {
    let presets: Set<Config.LoRaConfig.ModemPreset>
    let defaultPreset: Config.LoRaConfig.ModemPreset
    let licensedOnly: Bool
}

extension LoRaRegionPresetMap {
    func decoded() -> [Config.LoRaConfig.RegionCode: RegionPresetInfo]
}

A region_groups entry whose group_index is out of range is skipped defensively, which tolerates malformed or forward-compatible data.

AccessoryManager.processFromRadio(_:) dispatches the new .regionPresets variant to handleRegionPresets(_:) (in AccessoryManager+FromRadio.swift), which stores the decoded lookup on the connection model:

@Published var loRaRegionPresets: [Config.LoRaConfig.RegionCode: RegionPresetInfo] = [:]

It is reset to empty on disconnect (updateState → .idle/.discovering), so the map always reflects the currently connected radio. There is no SwiftData persistence — the radio re-sends it every handshake, and the LoRa screen only edits a connected node.

Firmware gating

The new 2.8 regions and presets must not be settable on radios running 2.7.x or earlier, which have no band table for them and would silently clamp the selection. RegionCodes and ModemPresets (in LoraConfigEnums.swift) mark the 2.8 additions and expose firmware-aware selection helpers:

RegionCodes.selectable(supports2_8: Bool) -> [RegionCodes]
ModemPresets.selectable(supports2_8: Bool) -> [ModemPresets]

When supports2_8 is false, the amateur/ham regions (itu*), the EU 866 / narrow regions, and the Lite / Narrow / Tiny presets are dropped from the pickers. The flag is derived from the connected radio via the existing AccessoryManager.checkIsVersionSupported(forVersion: "2.8.0"). The legacy userSelectable accessors are retained for callers with no firmware context (e.g. the discovery scan) and are equivalent to selectable(supports2_8: false).

UI integration

LoRaConfig.swift reads accessoryManager.loRaRegionPresets and applies these rules:

Filter — when Use Preset is on, the preset picker (availablePresets) is the firmware-gated list intersected with the selected region’s legal set. It never renders empty: an absent region or absent message falls back to the full gated list.
Default preset — switching region runs applyRegionPresetDefault(forRegion:), which delegates to the pure, unit-tested ModemPresets.presetToSelect(…). A factory-flashed node (region still unset) defaults to Long Turbo when US is selected; otherwise, if the current preset is not legal in the new region, it selects that region’s default_preset.
Licensed bands — when the region’s licensed_only is set, a warning row is shown, coordinated with the operator’s is_licensed flag in User Config.
EU auto-swap — the firmware may swap the EU sibling regions (EU_868 / EU_866 / EU_N_868) on a preset change. The screen dismisses on save and re-reads the persisted (possibly swapped) region on reopen, so the picker stays consistent.

Semantics (the load-bearing rules)

Rule	Behavior
Region absent from map	No constraint — show the full (firmware-gated) preset list.
Whole message absent (pre-2.8)	No constraint — keep unconstrained behavior; never block the screen waiting for it.
`default_preset`	Always a member of the group’s `presets`; used to re-select when the current preset becomes illegal.
`licensed_only`	Ham/amateur band — warn/gate and coordinate with `is_licensed`.
Source of truth	The firmware still validates/clamps; the map is a UI guard, not a correctness boundary.

Regions with no firmware band table (EU_874, EU_917, ITU*_70CM) are simply absent from the map and carry no constraint.

Files

File	Role
`Meshtastic/Enums/LoraConfigEnums.swift`	`RegionCodes`/`ModemPresets` cases, gating helpers, `RegionPresetInfo`, `LoRaRegionPresetMap.decoded()`
`Meshtastic/Accessory/Accessory Manager/AccessoryManager.swift`	`loRaRegionPresets` storage, `.regionPresets` dispatch, disconnect reset
`Meshtastic/Accessory/Accessory Manager/AccessoryManager+FromRadio.swift`	`handleRegionPresets(_:)`
`Meshtastic/Views/Settings/Config/LoRaConfig.swift`	Region/preset pickers, filtering, default-preset switch, licensed warning
`MeshtasticTests/LoraDeviceEnumTests.swift`	`LoRaRegionPresetMapTests`, `LoRaFirmwareGatingTests`

Testing

LoRaRegionPresetMapTests decodes the firmware’s reference table (spec §9 — six preset groups) and asserts the per-region presets, defaults, and licensing — including that two groups sharing the same preset list keep distinct licensing, that an out-of-range group_index is skipped, and that absent regions carry no entry. LoRaFirmwareGatingTests covers the selectable(supports2_8:) gating for both enums.