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# Two LoRa profiles on one radio

`radio2` lets one LoRa transceiver alternate between two frequencies or modulation
settings. It is useful for listening to two networks, or keeping your usual
channel available during a LoRa firmware update.

There are **at most two active profiles**. `tempradio` temporarily replaces
`radio`; `tempradio2` temporarily replaces `radio2`. These are time-shared receive
windows, not simultaneous receivers. Receiving or transmitting a packet on one
profile makes the other unavailable until that packet finishes.

The second-profile commands are shared by repeater, Companion, room server,
sensor and standalone terminal-chat firmware with a LoRa radio. ESP-NOW-only
devices reject LoRa profile commands. KISS is a raw host-controlled modem: it
exposes equivalent RAM-only binary `SetRadio2`/`SetTempRadio2` commands and
logical KISS Data ports, documented in [the KISS modem protocol](kiss_modem_protocol.md).
It does not use the Mesh CLI's persistent profile file or Mesh retry queues.

## Quick setup

Keep the primary channel configured with `radio`, then add the second:

```text
set radio2 910.5,500,8,5,rx
get radio2
get radio2.status
```

The tuple is **frequency in MHz, bandwidth in kHz, spreading factor, coding-rate
denominator, mode, optional preamble in symbols**. `5` means coding rate 4/5.

| Mode | Receive on profile 2 | Transmit on profile 2 |
| --- | --- | --- |
| `rx` | Yes | Only infrastructure replies explicitly configured with `tx.reply ... force` |
| `rxtx` (also `rx&tx`) | Yes | Yes |
| `off` | No | No |

For transmission on both permanent profiles:

```text
set radio2 910.5,500,8,5,rxtx
```

The same encoded message is queued separately for each allowed transmit profile.
Each has its own direct/flood retry slots and channel-busy backoff. A forwarding
echo on one profile cannot cancel the other profile's retry. Packet storage and
the physical transceiver's airtime budget are shared; exhausted queues can still
drop packets.

## Keep the main channel during an update

```text
set tempradio2 910.5,500,8,5,rxtx,120
get tempradio2
```

This enables the second profile for 120 minutes (2 hours). Locally generated
LoRa OTA requests use the temporary second profile. Infrastructure OTA responses
follow `tx.reply` below (both TX-capable profiles by default). Ordinary local traffic stays
on the primary profile by default. Use an OTA-capable build and the usual OTA
setup on every participating node; a temporary profile does not add OTA support
to firmware built without it.

Local settings take effect after a short reply allowance. On repeaters, immediate
remote `radio2`/`tempradio2` changes (including `off`) wait until their exact reply
copies finish, with at least one successfully transmitted. A reply that cannot
be queued or whose copies all fail cancels the change. Queued replies have a
five-minute deadline; an already-transmitting copy may finish under the normal
radio watchdog. This confirms transmission, not reception by the remote client.

Permanent remote changes are prepared in an uncommitted file before replying;
the saved configuration is replaced only after reply transmission. If that
replacement fails, the old channel remains active and the commit retries.
Local `get radio2.status` reports this pending state. Roles without the tracked remote
reply path require local USB for these immediate secondary-profile changes.

Temporary periods and schedules live in RAM and disappear on reboot. Waiting
for a reply does not extend a temporary lease. Timer expiry also uses monotonic
time, so setting the clock backwards cannot extend a temporary session.

## Repeater, room-server, and sensor replies

These roles default to **`tx.reply both`**: locally generated replies are queued
on `radio` and on an active `radio2` that permits TX. This includes replies to
remote CLI/login/telemetry requests, ACKs, returned paths, delayed GPIO command
completion, room subscription posts, and locally served LoRa OTA catalog,
manifest, data, proof, and leaves responses. Each copy has its own retry state.
Forwarded packets, periodic adverts, sensor pushes, and OTA requests continue
to use the normal crossing rules.

```text
get tx.reply
set tx.reply both
set tx.reply both force
set tx.reply radio
set tx.reply auto
```

| Choice | Replies transmit on |
| --- | --- |
| `both` | Primary plus an active `rxtx` second profile. Default. |
| `radio` | Primary only. |
| `radio2` | Second only; no primary fallback. |
| `auto` | Normal `radio2.cross` behavior, including permanent/temporary isolation. |
| `off` | Neither profile. This also suppresses remote CLI replies and ACKs. |

Append **`force`** to `both` or `radio2` to allow these replies on an active
second profile configured as `rx`. Without `force`, `rx` remains receive-only.
Sending the command again without `force` removes the override. It never turns
on `radio2 off`, changes the saved `rx` mode, or enables ordinary forwarding/TX
there. Existing crossover packet filters still apply to the extra copy.

The explicit choices override `radio2.cross`, including `off` and mixed
permanent/temporary profiles. `radio` means the active primary profile,
including `tempradio`; `radio2` also includes an active `tempradio2`.
For example, an OTA source can retain its normal channel while allowing OTA
and management responses on a temporary receive profile:

```text
set tempradio2 910.5,500,8,5,rx,120
set tx.reply both force
```

The source must have OTA support and an active temporary-radio session as
usual. A node fetching an update still needs `rxtx` for its OTA requests.
Forcing replies does not change OTA's receive gates, scan timing, or preambles.

This setting survives reboot; older saved profiles adopt `both` without force.
The getter reports when the chosen second profile cannot transmit. Already
queued replies retain their choice; disabling/changing a profile invalidates
stale queued packets. A parameterized repeater `tempradio` command waits for
both admitted reply copies to drain before changing the primary settings;
at least one must transmit successfully. Those tracked replies omit alternate
paths and transport retries so no late success copy can outlive the handoff.
Queue capacity and the shared transceiver's airtime budget still limit delivery.
OTA data/proof admission counts both copies against its queue credit and
reserves receive capacity before allowing the response.

Companions use the per-contact/channel choices below; `tx.reply` is an
infrastructure setting.

## Companion messages on both profiles

To send ordinary Companion messages on both `radio` and an active `tempradio2`,
configure the temporary profile in `rxtx` mode and enable crossing:

```text
set radio2.cross on
get tempradio2
get radio2.cross
get radio2.status
```

`rxtx` permits transmission on the second profile; `radio2.cross on` copies new
messages between the two profiles. `TX=a,b` reports primary and secondary
transmit counts. Crossing also applies to OTA traffic.

The crossing setting is saved and remains enabled after the temporary session
ends or the node reboots. Run `set radio2.cross auto` to restore the default
isolation between permanent and temporary profiles. The firmware picker's
Companion tempradio2 instructions include both choices and the status commands.

## Companion TX routing by contact or channel

Companions can save a transmit choice for each contact and each configured
channel. The commands apply to messages sent from the phone app, USB/BLE/TCP
Companion clients, and the text terminal:

```text
set tx.user "Alice Jones" radio2
get tx.user "Alice Jones"
set tx.channel 0 both
get tx.channel 0
set tx.channel #wardriving radio
get tx.channel #wardriving
```

Channel indices match the app and the terminal's `channels` list; Public is
normally slot `0`. Names must match exactly, including capitalization and any
leading `#`. Quotes always select a literal name, so `"1"` is a channel named
`1`, while unquoted `1` selects slot 1. Quote contact names beginning with
`key:` to distinguish them from public-key selectors. Duplicate names are
rejected: use the channel index or a contact's public key instead.

| Choice | Locally addressed traffic transmits on |
| --- | --- |
| `auto` | Existing behavior, including `radio2.cross` and temporary-profile isolation. This is the default. |
| `radio` | The primary profile only. |
| `radio2` | The second profile only; sending fails if it is off or RX-only. |
| `both` | The primary profile and the second profile whenever the second is enabled for TX. |
| `off` | Neither profile for this contact/channel. Reception stays enabled. |

Explicit choices override `radio2.cross`, including `off` and the isolation
between a permanent and temporary profile. They do not turn on radio2 or
change its `rx`/`rxtx` mode. For example, leave `radio2.cross auto` and use
`set tx.channel 0 both` to send Public messages on both `radio` and an active
`tempradio2`, while other channels keep their default routing.

`radio` means the currently active primary profile, whether permanent or
`tempradio`; `radio2` similarly includes `tempradio2`. There are still at most
two active profiles. Getters show the saved choice and `active=` for newly
initiated messages with the current profile configuration. A temporarily
unavailable second profile is reported explicitly.

Contact selection uses the full stored public key after resolving a unique
name or key prefix. It never routes by the short on-air destination hash.
For key selection, prefix 12–64 hexadecimal digits (whole bytes) with `key:`:

```text
set tx.user key:0123456789AB radio2
get tx.user key:0123456789AB
```

Replace the example prefix with your contact's key; use more digits if it is
ambiguous. `get tx.user` and `get tx.channel` report override counts and query
syntax. To return a target to the global behavior:

```text
set tx.user "Alice Jones" auto
set tx.channel 0 auto
```

A user's setting covers addressed texts, login/CLI/telemetry requests, replies,
ACKs, and returned paths to that contact. Thus `off` also prevents ACKs to
that contact. Channel settings cover group text and group data, including
an explicitly routed group datagram. Contact choices do not filter other
people's messages inside a group channel. Adverts, raw traces, raw packets,
and OTA packets without a contact/channel destination retain global routing.
Packets and their retries already queued retain the choice used when created;
changing or disabling the radio profile still invalidates stale queued work.
Message timeout estimates use the selected profiles' airtime, independently
of the scanner's current receive profile.

Choices survive reboot and normal phone-app updates to the same contact or
channel key. Replacing a channel's key or deleting/replacing a contact clears
its choice. They use reserved bytes in existing saved records, so record
sizes and the phone protocol are unchanged. Older firmware ignores these
bytes and may reset the choices when it saves the records.

## Companion channel-name routing aliases

Companions recognize the case-sensitive prefixes `r2-` and `mt-`, immediately
after the optional leading `#`. Keep the prefix in the app's displayed name.
For MeshCore aliases, the firmware strips exactly one prefix when deriving an
automatic hashtag key:

```text
#emergency       -> hashtag key for #emergency
#r2-emergency    -> the same key for #emergency
#mt-emergency    -> the same key for #emergency only in MeshCore fallback mode
```

Only the app's automatic, name-derived hashtag key is normalized; a supplied
private key is not replaced. Non-hashtag names such as `r2-Private` also retain
their supplied key. Empty or nested prefixes (`r2-`, `#r2-mt-emergency`) are
rejected. MeshCore hashtag names remain case-sensitive.

When radio2 is configured (`rx` or `rxtx`), `r2-` binds the channel to radio2 for
both send and receive, including emergency retransmissions. It overrides global
crossing and cannot be changed with `set tx.channel`; rename the channel to
remove the binding. RX-only radio2 cannot send. If radio2 is off/unconfigured,
ignore the routing prefix and use ordinary MeshCore routing instead. The key
stays the same as radio2 is enabled, disabled, or a temporary window expires.

If both the ordinary and `r2-` slots have the same key, a packet received on
radio2 selects the `r2-` slot; a packet received on radio1 selects the ordinary
slot. Global packet deduplication still delivers each packet once, not once in
each slot. Receiving a radio2-only channel on the wrong profile does not mark
that authenticated packet seen, so it can still arrive later on radio2.

The saved channel record retains the original displayed name and app-supplied
key for editing and sharing. Runtime copies resolve the actual wire key.
Repeater/room/sensor hashtag behavior is unchanged; those nodes can join the
canonical MeshCore channel (`#emergency`). Older Companion firmware does not
recognize these aliases.

### Meshtext channel chat

`MESH_ENABLE_MESHTEXT_CHAT` enables the text-only Meshtext backend in the
Companion. It defaults on for ESP32-S3 **Full Companion** builds using
SX1262 LoRa and for the RAK4631 **Full Companion** starting with 1.17.1.10
preview3. An ESP-NOW primary and other builds default off. RAK4631 1.17.1.10
preview2 and earlier builds did not include this backend. This is not
a replacement for stock peer firmware or a cross-protocol bridge.

In an enabled build, an `mt-` name always requests Meshtext, even if radio2 is
off or setup is blocked. It never falls back to sending MeshCore frames. In a
feature-disabled build, `mt-` remains an ordinary MeshCore naming alias while
radio2 is off; with radio2 configured, MT channel changes/sends are unsupported.
The `r2-` MeshCore behavior above is unchanged in either build.

With the region configured, join `#mt-longfast`, for example, through the app's
normal hashtag-channel editor. A recognized preset name selects the stock
peer channel name (`LongFast`) and, **only for an automatically
name-derived hashtag key**, the expanded public `AQ==` key. This public key is
not a secret. An explicitly
supplied private AES-128 or AES-256 key stays private and unchanged. A custom
name such as `mt-Private` uses the exact tail (`Private`) as its wire name and
the supplied key; custom wire names are limited to 11 bytes and need a manual
radio2 profile or another MT channel with a recognized preset. Preset names
are ASCII case-insensitive; the `mt-` marker is still case-sensitive.

Recognized aliases and modulation are:

| Alias tail | Stock wire name | BW (kHz) | SF | CR |
| --- | --- | ---: | ---: | ---: |
| `shortturbo` | `ShortTurbo` | 500 | 7 | 5 |
| `shortfast` | `ShortFast` | 250 | 7 | 5 |
| `shortslow` | `ShortSlow` | 250 | 8 | 5 |
| `mediumturbo` | `MediumTurbo` | 500 | 9 | 5 |
| `mediumfast` | `MediumFast` | 250 | 9 | 5 |
| `mediumslow` | `MediumSlow` | 250 | 10 | 5 |
| `longturbo` | `LongTurbo` | 500 | 11 | 8 |
| `longfast` | `LongFast` | 250 | 11 | 5 |
| `longmod` or `longmoderate` | `LongMod` | 125 | 11 | 8 |
| `longslow` | `LongSlow` | 125 | 12 | 8 |

The selected region must have room for the bandwidth; for example, 500 kHz
presets are unavailable in the supported EU868 plan. Use these CLI commands:

```text
get mt.status
get mt.region
get mt.slot
get mt.hops
get mt.node
get mt.shortname
set mt.node !12345678
set mt.node default
set mt.region auto
set mt.region us
set mt.slot 0
set mt.hops 7
set mt.shortname HALO
set mt.shortname default
send mt.nodeinfo 0
get radio2
set radio2 auto
```

`mt.region` accepts `auto`, `us`, `eu868`, `eu433`, or `anz`. `auto` infers US
only from a primary frequency at least 902 MHz and below 915 MHz, EU868 from
869.4–869.65 MHz, and EU433 from 433–434 MHz. The US/ANZ overlap at 915–928 MHz
is ambiguous: explicitly select `us` or `anz`. `mt.slot` is a 1-based frequency
slot, or `0` for the stock preset-name-derived slot; unavailable slots are
blocked. Check `get mt.status` after configuration; a successful settings save
does not mean the MT backend is active.

Outgoing MT messages default to a hop limit of **7**. `set mt.hops <0..7>`
changes this budget, and `get mt.hops` or `get mt.status` shows it. `0` sends
only the initial over-air hop with no forwarding budget; larger values permit
protocol-compatible peers to forward within that budget. The Companion itself still
does not relay MT packets.

`get mt.node` shows the effective Meshtext sender node ID. By default it is
SHA-derived from the MeshCore public identity and remains stable for that
identity. `set mt.node !12345678` sets a saved override; exactly eight hexadecimal
digits are required, with or without the leading `!`. Input is hexadecimal,
not decimal, and is never silently truncated. IDs `00000000` through `00000003`
and `ffffffff` are reserved and rejected. `set mt.node default` clears the
override and restores the identity-derived ID.

The example ID is illustrative: choose an ID unique among your protocol-compatible
peers. Collisions can merge different senders into one identity and interfere
with packet deduplication. Changing the MT ID does not alter the MeshCore
private key, reset the outgoing packet-ID sequence or send automatic traffic.
Settings changes are refused while an MT transmission is
pending. Neither node IDs nor text labels are authenticated.

`set mt.shortname <label>` saves a Meshtext-only NodeInfo name of 1–4 Unicode
scalar characters, with valid UTF-8 and at most 16 encoded bytes. Combining
characters count separately. `get mt.shortname` shows the saved/effective
name. Stock NodeInfo accepts only four UTF-8 **bytes**, so the effective wire
name is the longest complete UTF-8 prefix that fits. The saved value is not
changed. `set mt.shortname default` clears the override and uses the last four
hexadecimal digits of the effective MT node ID. This does not change the
MeshCore node name, add a label to chat text or transmit anything.

`send mt.nodeinfo <channel slot>` explicitly queues **one** standard
`NODEINFO_APP` broadcast on the selected configured MT channel. The slot is
the Companion channel index, not `mt.slot` (the frequency slot). The packet
contains the actual sender ID, the global MeshCore node name as its long name
(UTF-8-safe truncated to 24 bytes), the effective short name, `CLIENT_MUTE`
(no relaying), and the no-DM flag. It omits MAC, public keys and unsupported
metadata. The usual radio2 TX-mode, pending-TX, airtime and profile guards
apply. The reply says **queued**, not delivered or acknowledged.

There are no automatic NodeInfo advertisements: not at boot, on a timer, when
names change, when chat is sent, or in response to received packets. Received
NodeInfo is still ignored; this backend does not maintain a node database.

Region, frequency slot, hop limit, shortname and node-ID override are saved
atomically together; changing one preserves the others. Current 40-byte `MT03`
settings include both overrides. New firmware accepts valid legacy
`MT01`/`MT02` settings and defaults the shortname to the sender-ID suffix and
the node ID to the MeshCore identity; `MT01` also defaults the hop limit to 7.
Older MT firmware cannot read `MT03`, so downgrading does not preserve access
to these settings. Invalid or unsupported stored settings block MT operation
rather than silently selecting another network.

Private channels can be provisioned directly through the Companion CLI:

```text
set mt.preset <longfast|shortturbo|...>
set mt.channel <slot> <mt-name> <32/64 hex digits|AQ==>
get mt.channel <slot>
delete mt.channel <slot>
```

`set mt.preset` accepts the recognized presets above and explicitly saves a
manual `rxtx` radio2 RF tuple using the current region and frequency slot. It
is not an automatic owner: deleting the channel does not remove that saved RF
configuration. Set region/slot first; changing them later does not overwrite
the manual frequency, so rerun `set mt.preset` if you intend to retune it.

`set mt.channel` accepts a 32-digit hexadecimal AES-128 PSK, a 64-digit
hexadecimal AES-256 PSK, or the literal `AQ==` for the public key. It does not
accept arbitrary Base64 private keys. The stored format interprets an all-zero
upper 16-byte half as AES-128, including in a 64-digit input; use a nonzero
upper half for AES-256. Slot numbers are zero-based and build-specific, as in
the app. `get mt.channel` reports name, wire name and AES size, never the PSK.
The firmware console masks key input echo; keep your client-side logs and
stored keys private as well. SET and DELETE save transactionally and restore
the previous channel if storage fails. DELETE applies only to an MT channel,
not a MeshCore slot.

For a private channel named `Team` on a protocol-compatible peer:

```text
set mt.region us
set mt.preset longfast
set mt.channel 1 mt-Team <your-32-or-64-hex-digit-key>
get mt.channel 1
get mt.node
set mt.shortname HALO
get mt.status
send mt.nodeinfo 1
channel 1 Hello
```

Replace the key placeholder with your actual hexadecimal PSK and send after
`get mt.status` reports active. The peer must use the same preset, frequency,
PSK and exact case-sensitive wire name `Team`; `mt-` is only the local marker.
Alternatively, `set mt.channel 1 mt-longfast <your-key>` preserves a private
PSK but uses wire name `LongFast` and can acquire automatic RF without
`set mt.preset`, provided radio2 automatic ownership is permitted. This route
is available for both 128-bit and 256-bit private keys even when the stock app
cannot provision or export the latter.

When radio2 was never manually configured, a recognized preset can acquire an
automatic `rxtx` profile. Its RF tuple is RAM-only and stays available for RX
while the required channels exist. Removing the last MT channel, losing its
last recognized-preset dependency, or detecting a conflict releases only the
automatic profile. Explicit manual RF settings are retained: named aliases
must match their BW/SF/CR and fit the selected region, but do not overwrite
their frequency. The runtime MT overlay uses its required 16-symbol preamble;
the saved manual preamble is retained.

`set radio2 off` is an explicit manual veto, including after reboot. Older
saved off profiles are conservatively treated as manual. Local
`set radio2 auto` clears the saved manual RF/off choice and permits automatic
ownership after two seconds; it rejects pending changes, leases and schedules
rather than cancelling them. `get radio2` distinguishes `auto-owned`, `off (manual)`
and `off (automatic allowed)`. Temporary profiles, scheduled changes and reply
commit barriers take precedence and can suspend MT operation. Automatic
cleanup does not undo later manual edits.

All MT channels share this one secondary modem profile. Different recognized
presets, or mixing any MT and `r2-` channels, are rejected instead of selecting
whichever channel was edited last. Loaded conflicts also block MT traffic.
Neither `radio2.cross on` nor MeshCore channel routes cross MT frames between
protocols.

The app uses its existing channel index/text commands and receive events.
Outgoing MT chat is plain text exactly as entered, with the sender node ID in
the standard radio header. It contains no custom name envelope or NodeInfo.
Incoming text uses the exact sender-ID prefix `!12345678: ` before the received
payload when passed to the MeshCore app. Changing the shortname only changes
future manually requested NodeInfo, not chat or the packet's sender ID;
`set mt.node` changes the actual Meshtext sender ID. Neither setting change
emits advertisements. A successful
send response means **queued**, not acknowledged by a remote node. This backend
does not relay MT packets or provide ACKs, administrative commands, direct
messages, automatic node-info adverts or a node database. MeshCore emergency forwarding
does not apply to MT traffic. Interoperability is with stock peers' PSK channel
text using AES-CTR, not AES-CCM. AES-CTR channel traffic is not authenticated;
successful decoding is not proof of sender identity.

The codec supports AES-128 and AES-256 and up to 228 UTF-8 bytes of wire text,
without an added label/node-ID prefix. The standard app channel editor
still provisions 16-byte keys. An MT-only 32-byte binary SET/opt-in GET
extension is available for capable clients, with protection against legacy
16-byte edits truncating an existing 256-bit key; see
[Companion protocol](companion_protocol.md#4-set-channel). This does not give
stock apps seamless 256-bit provisioning or sharing. Current V3 Companion
receive events carry at most 165 text bytes **including the node-ID prefix**;
longer incoming MT text is UTF-8-safe truncated for the app.

Radio1 and radio2 still time-share **one physical radio**. The device cannot
receive either network while tuned to the other or transmitting; long MT
airtime, particularly LongFast, can leave substantial MeshCore receive gaps.
The compatible protocol's fixed short preamble also does not provide the scan-aware long
preamble described below. Do not treat this as continuous coverage of both
networks or guaranteed message delivery.

## Choose whether traffic crosses between profiles

```text
get radio2.cross
set radio2.cross auto
set radio2.cross on
set radio2.cross off
```

| Active primary | Active secondary | `auto` (default) | `on` | `off` |
| --- | --- | --- | --- | --- |
| `radio` | `radio2` | Cross | Cross | Isolated |
| `tempradio` | `tempradio2` | Cross | Cross | Isolated |
| `radio` | `tempradio2` | Isolated | Cross | Isolated |
| `tempradio` | `radio2` | Isolated | Cross | Isolated |

This table describes MeshCore profiles. A Meshtext secondary profile is
always isolated, including with `radio2.cross on`.

These are the global rules used by Companion targets set to `auto`; an explicit
contact/channel choice above overrides crossing for its own outbound packets.
Ordinary crossing respects `rx`. The infrastructure-only `tx.reply ... force`
override above permits locally generated replies on that profile.
With crossing allowed, a packet received there may still be forwarded on the
primary profile. Existing routing, forwarding and packet-filter settings apply.
An RX-only `tempradio2` also blocks locally generated OTA requests under
`auto` or `off`; they do not fall back to the normal primary channel. Use `rxtx`
for a fetching node that needs to exchange requests and data. Infrastructure
OTA responses follow `tx.reply` independently of this crossing table.

## Preamble

Append the preamble to the end of a command:

```text
set radio2 910.5,500,8,5,rxtx,88
set tempradio2 910.5,500,7,5,rxtx,120,128
set radio 909.5,62.5,7,5,32
set tempradio 909.5,62.5,7,5,120,32
```

Existing primary `radio`, `tempradio`, `radioat` and `tempradioat` commands accept
the optional trailing preamble where those primary commands are supported by
the role. Getters include the preamble. Omit it, or use `auto`/`0`, to calculate
it automatically. Explicit values are used as entered, subject to the radio's
limits and safe airtime arithmetic.

Automatic dual-profile preambles round **up to a multiple of eight**, with a
32-symbol minimum and a 128-symbol maximum. When a second profile activates,
the radio first self-tests four successful RX-to-RX switches in each direction
using the actual tuples. It defers the test while receiving, transmitting or
busy, and never counts a failed switch. The 128-symbol automatic preamble is
provisional until the test completes. The largest successful hop, rounded up
with a **10% guard**, then supplies the per-switch allowance for both the
automatic preambles and the scan dwell. There is no fixed switch-time floor.
The measurement is reset when either profile changes, including when a
`tempradio2` session starts or ends; it is not saved to flash.
The rapid startup hops briefly interrupt reception on each channel; a new
packet beginning during this test may be missed. An already detected packet
defers the test instead of being interrupted.

Each idle scan starts with **4.6 symbols on the slower
profile**, then spends the remaining budgeted time on the faster profile,
also with a **4.6-symbol floor**. Slower
means a longer LoRa symbol (`2^SF / bandwidth`), regardless of profile number.
The slower preamble sets the return deadline. The calculation allows two slow
visits within that preamble, reserving the self-tested, 10%-guarded switch time
per hop. There is no extra fixed main-loop allowance. Fast-channel transmit
preambles include sixteen acquisition symbols.
For a primary SF7 / 62.5 kHz profile with a 763 us measured maximum switch
(840 us after the 10% guard, from the BLE-on T1000-E trial):

| Secondary profile | Automatic secondary preamble | Previously tested explicit preamble | Primary preamble |
| --- | ---: | ---: | ---: |
| SF9 / 500 kHz | 32 | 32 | 32 |
| SF8 / 500 kHz | 40 | 64 | 32 |
| SF7 / 500 kHz | 64 | 80 | 32 |

With preamble 32 on that slower profile, its visit is 9.421 ms and the faster
visit is 21.667 ms, plus the actual switching time. Increasing the slow preamble
also increases the time available on the fast channel. If the symbols are equal
in length, the primary profile goes first. Detected packets hold the current
channel until reception finishes.

The SF8 / 500 kHz value is calculated from the same formula as every other
profile; the older pair-specific 88-symbol floor has been removed. The explicit
values come from [historical production validation](test-results/radio_profiles_validation.md):
the final fast-channel attempts each received 50/50 packets at 4.8 slow symbols.
Automatic values use the measured switch allowance below.
Those explicit-preamble tests used the older 4.8-symbol policy; they do not
validate the newer 4.6-symbol slow dwell. The
[4.6/0.3 ms two-profile bench](test-results/radio_dwell_policy_validation.md#hardware-context) received 197/200
at SF7/62.5 + SF8/500 with explicit 32-symbol preambles. The newer four-channel
5.1/6.1/7.7 tests also had misses, so this is a timing policy, not a claim of zero packet loss.
The automatic fast preamble covers the blind interval during the slow visit,
both switches and the acquisition margin. These settings do not guarantee
reception during overlapping packets or long pauses in the firmware loop.
**Transmitters on each channel also need a long enough preamble.** Changing the
receiver's setting does not lengthen packets sent by other nodes.

### Chirp calculator and warnings

`get radio2.timing` (alias `get radio.timing`) reports the active pair in
`radio,radio2` order: dwell in chirps, recommended preambles in symbols, and
the switching/loop allowances. Before calibration it reports `timing self-test
pending` and the provisional preambles. On nRF52 boards, enabling `radio2`
uses RTC2 for both retune timing and scan visits (about 31 us resolution);
turning `radio2` off stops RTC2 and returns to the usual `micros()` clock.
Previously, the nRF52 `micros()` fallback counted 1,024 Hz RTOS ticks: a real
sub-millisecond retune could be reported as exactly 977 us, and two ticks as
1,953 us. Those old numbers are timer artifacts, not measured RF costs.
For SF7/62.5 on `radio` and SF8/500 on `radio2`, one live BLE-on read returned:

```text
> chirps=4.60,42.84; need=32,40; switch=706us; loop=0us; test=4/4,4/4 ready; WARN recommended preamble: radio2=40
```

Later good hops in another BLE-on trial raised the measured maximum to 763 us
(840 us with the 10% guard); the recommendation stayed at 40 symbols.

The measured switch duration is wall time, so an interrupt during the hop is
included. Bluetooth's SoftDevice may still preempt application code; this
clock correction does not stop it. Ordinary Companion/USB work in the main
loop does not run inside the synchronous retune, but it can delay when the
next scan visit begins. The zero fixed loop allowance is not a guarantee of
lossless reception under arbitrary application load.

`WARN recommended preamble` identifies **each** profile whose recommendation
exceeds the standard 32 symbols or its explicitly selected value. For example,
with SF7/62.5 on the primary profile, `set radio2 910.5,500,7,5,rx,32`
initially replies with `timing self-test pending`. Once active and measured,
`get radio2` warns:

```text
> 910.500,500.000,7,5,rx,32; WARN recommended preamble: radio2=64; short override: radio2
```

Successful `set radio ...` replies also include the recommended preamble for
each affected profile, calculated with the requested settings. A `short override`
note identifies an explicit value below the estimate; it is not silently
rewritten. Warnings are also included in profile settings/getters, scan info,
temporary settings and schedule acknowledgments. These preamble-bearing replies
also include `switch=547us` (or the current measured value) after the self-test
for that exact profile pair. The first ACK for a new pair says `timing self-test
pending` instead: it is sent before activation, so it cannot contain the future
measurement. Query `get radio2` after activation to see the measured value beside
the resulting preamble. `off` disables the dual-profile
warning. `get radio2.status` shows self-test progress and the resulting guarded
switch budget; its separate `max` field remains a lifetime diagnostic that can
include failed/rolled-back retunes and is not used for calibration. If the
recommendation exceeds 128, it additionally reports
`WARN need >128`; an automatic preamble stays at 128, which may not be enough
for reliable reception on that pair. Explicit preambles are not rewritten and
still use the radio's ordinary validation limits. A timing readout does not
change settings or transmit a packet.

The shared `RadioProfiles::calculateChirpTiming()` function accepts both tuples,
optional visit times in microseconds, a per-switch allowance and loop margin.
Using microseconds throughout:

```text
T[i] = 2^SF[i] * 1000 / BW_kHz[i]
slow = profile with the longer T (radio wins ties)
L[slow] = max(requested_visit_us[slow], ceil(4.6 * T[slow]))
L[fast] = max(requested_visit_us[fast], ceil(4.6 * T[fast]))
O    = 2 * switch_us
C    = L[radio] + L[radio2] + O

P[slow] = round_up_to_8(max(32, 2 * C / T[slow]))
P[fast] = round_up_to_8(max(32, (L[slow] + O) / T[fast] + 16))
```

Automatic selection uses the minimum visits to choose a preamble, then allocates
the fast visit from half the slow preamble's duration. Diagnostics feed the
actual allocated visits back into the same function, including longer visits
caused by an explicit slow preamble. Too-short slow preambles that cannot fit
both minimum visits remain rejected by the existing configuration validation.

The automatic scheduler uses these same role-specific minima and computes:

```text
slow_dwell = ceil(4.6 * T[slow])
fast_dwell = max(ceil(4.6 * T[fast]),
                 floor(P_configured[slow] * T[slow] / 2 - slow_dwell - O))
```

For the tested SF7/62.5 + SF8/500 pair with slow preamble 32, this yields
9,421 us slow and 21,197 us fast (41.40 fast chirps) with the 1,075 us guarded
switch allowance above. Swapping `radio` and `radio2` swaps the allocations automatically.

Production scheduling and automatic preambles use the **self-tested maximum
successful switch plus 10%**, without an additional fixed loop allowance. Subsequent
successful hops can only raise that allowance until the next profile change.
The measured recommendation is rounded up to eight symbols and capped at 128
for automatic settings. The calculator and warnings retain the *uncapped*
recommendation so a slow board is not shown as safe merely because it hit the
limit. Older V4 tests peaked at 836 us (827 us in the 4.6/0.3 ms run), and
Indicator reached 8428 us; these are historical measurements, not default
budgets for other boards.
The model preserves two slow-profile return opportunities and the existing
16-symbol fast-profile acquisition allowance. These are conservative policies,
not a fitted success curve, and neither packet overlap nor arbitrary application
stalls can be made safe by a finite preamble recommendation.

See the [implementation and validation notes](test-results/radio_dwell_policy_validation.md).

## Schedule the second profile

Use UTC Unix timestamps (seconds), or `+N` for N whole minutes from now:

```text
set radioat2 910.5,500,8,5,rxtx,START[,PREAMBLE]
set tempradioat2 910.5,500,8,5,rxtx,START,END[,PREAMBLE]
get radioat2
get radioat2 1
get tempradioat2
get tempradioat2 1
del radioat2 1
del tempradioat2 all
```

Replace `START` and `END` with timestamps or `+N`, and the optional `PREAMBLE`
with a number; omit the square
brackets. Each schedule family has four slots. Times must be in the future and
within 24 days. Overlapping temporary second-profile sessions are rejected.
`radioat2` changes the saved second profile when it starts; `tempradioat2`
restores the saved profile at its end. Pending schedules do not survive reboot.

For example, `set tempradioat2 910.5,500,8,5,rxtx,+5,+15` starts in 5 minutes
and restores in 15 minutes (10 minutes active). Both offsets are measured from
the same node-clock snapshot when accepting the command, not from each other.
`set radioat2 910.5,500,8,5,rxtx,+5` schedules a saved change in 5 minutes.
Offsets must be positive whole minutes. Absolute and relative endpoints can be
mixed; bare numbers still mean UTC seconds. Existing clock requirements apply.

## Return to one profile

```text
set radio2 off
```

This saves the disabled state and cancels all second-profile temporary activity
and schedules.

```text
set tempradio2 off
```

This ends temporary second-profile activity, cancels its temporary schedules and
restores saved `radio2`. If the saved second profile is off, this returns to one
profile. Packets/retries bound to an expired or changed session are discarded.

## Power saving and diagnostics

Dual mode suspends RX power saving and MCU idle sleep so receive visits can run
promptly. The saved RX power-saving setting returns when profile 2 is off.
The scan uses **normal receive**, following the
[CAD/RX measurements](test-results/cad_scan_validation.md), with the updated 4.6-symbol dwell on the slower
channel, followed by the remaining fast-channel visit. It does not use CAD for scanning.
The separate CAD check before an initial transmission still follows `cad`.

SX1262 dual-profile mode keeps the oscillator running in XOSC standby between
visits, so each retune does not need to restart the TCXO. It restores the prior
standby policy when returning to one profile, together with the saved RXPS
setting. Radio reinitialization temporarily uses RC standby until the TCXO has
been configured again. Other radio families retain their existing behavior.
This does not disable the TCXO supply or its initial startup delay, and it is
not conditional on 500 kHz bandwidth. Keeping the oscillator on uses additional
power during the short standby intervals.

The switch-time self-test is not a forced settling delay or a proof of RF
acquisition. The earlier standalone
[keep-warm scan experiment](test-results/mixed_scan_validation.md) averaged about 1.19 ms
of overhead per hop (scan-cycle time minus both receive windows, divided by
two). That experiment used a leaner receive path; it is not a measurement or
guarantee of the production implementation. Measure the target board before
shortening its timing margins or transmit preambles.

The [production-path XIAO timing test](test-results/radio_profile_switch_validation.md)
measured **1.434 ms average / 1.467 ms maximum** with warm standby, compared
with **3.166 ms average** using RC standby: about **1.732 ms saved per hop**.
It covered 12,000 retunes across SF7/8/9 at 500 kHz paired with SF7/62.5 kHz.
These measurements include observing BUSY low, but exclude application/UI
scheduling and are not a packet-delivery qualification or a guarantee for
other boards, especially those using I/O expanders.

A same-image follow-up batching SF/BW/CR into one modulation command reduced
warm switching from **1.444 ms to 1.158 ms average** (batched maximum **1.198 ms**),
saving another **0.286 ms / 19.8%**. RadioLib's modulation caches and LDRO
calculation remain synchronized; frequency, preamble, packet guards, and RX
restart are unchanged. A later [HIL-only screening](test-results/radio_profile_switch_validation.md#expanded-screening-redundant-rx-setup-and-spi-v5)
tested redundant standby/IRQ/buffer/packet setup and SPI transfer changes.
Its fastest candidate measured 0.535 ms mean on XIAO but 8.203 ms on the
Indicator, whose radio GPIOs go through an I2C expander. The validated production
implementation now opts XIAO S3 WIO and Indicator LoRa into buffered 8 MHz SPI
and a guarded fast-RX state machine. The `heltec_v4_kiss_modem` and
`Station_G3_ESP32_kiss_modem` targets use the same guarded path only for KISS
dual-profile scanning; their normal board roles keep their established
HAL/timing policy. V4 uses its existing 160 MHz role override and Station G3
uses its base 240 MHz setting, but both still need an exact-image hardware
timing check before a nominal 600 µs target is claimed. It skips redundant
standby, IRQ mapping,
buffer-base writes and modem queries only during an owned continuous RX-to-RX
retune. Preamble/packet parameters (including the IQ workaround), stale-IRQ
clearing, RX commands and BUSY waits remain. TX, CAD, sleep, reset, RXPS and
failed commands revoke reuse; failed RX startup rolls back the profile.
Sleep entry uses standby and wake restores the existing TCXO voltage/delay.
Other variants do not opt in to faster SPI or the fast-RX state machine.
Within a valid owned fast-RX retune, identical acknowledged SF/BW/CR/LDRO
settings now reuse the previous modulation command: frequency-only hops omit
`SetModulationParams` (0x8B). A changed effective LDRO value also forces a write,
including when automatic LDRO policy changes. Ordinary setters and lost RX
context invalidate that acknowledgement; initial setup, reset, sleep, failed
commands and full RX setup conservatively reapply the tuple. Frequency,
preamble/packet setup, IRQ clearing and BUSY checks are unchanged. This follow-up
has [same-image hardware measurements](test-results/separated_radio_modulation_cache_validation.md):
frequency-only hops averaged 0.452 ms on XIAO and 7.601 ms on Indicator.
The mixed-bandwidth timing figures above predate it. Four-channel SF6 scans
still missed packets; faster switching is not proof of loss-free acquisition.
See [production and USB validation](test-results/radio_profile_switch_validation.md#production-integration-and-usb-recovery-v8)
for current measurements, lifecycle tests and limitations.
The Indicator result shows why each board now measures its own switch time.
That measurement adjusts automatic preambles and dwell, but it cannot verify
RF acquisition or lengthen packets transmitted by other nodes.

Single-channel noise-floor calibration and RSSI interference comparison are
suspended while scanning. Retries use the radio's preamble/header activity
indicators. LR2021 extra-SF side detectors are suspended and restored as well.

`get radio2.status` reports the active second-profile mode, MeshCore RX/TX counts
for each profile, switch count, switch failures, longest measured switch and
both effective preambles. A long switch time or rising error count indicates
that the chosen settings need investigation on that board.

`get radio2.scan` shows which profile goes first, the two idle receive-window
lengths in microseconds, and both effective preambles. It reports `off` in
single-profile mode.