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213 lines
15 KiB
Markdown
213 lines
15 KiB
Markdown
<!--- Copyright 2022 QMK --->
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<!--- SPDX-License-Identifier: GPL-2.0-or-later --->
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<!---
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*******************************************************************************
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"Y88P"
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*******************************************************************************
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--->
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# QMK Firmware XAP Specs
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This document describes the requirements of the QMK XAP ("extensible application protocol") API.
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## Types
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**All integral types are little-endian.**
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| Name | Definition |
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| -- | -- |
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| _struct{}_ | A structure of data, packing different objects together. Data is "compacted" -- there are no padding bytes between fields. Equivalent to a packed C-style `struct`. The order in which they're defined matches the order of the data in the response packet. |
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| _type[n]_ | An array of `type`, with array extent of `N` -- e.g. `u8[2]` signifies two consecutive octets. |
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| _u16_ | An unsigned 16-bit integral, commonly seen as `uint16_t` from _stdint.h_. |
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| _u32_ | An unsigned 32-bit integral, commonly seen as `uint32_t` from _stdint.h_. |
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| _u64_ | An unsigned 64-bit integral, commonly seen as `uint64_t` from _stdint.h_. |
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| _u8_ | An unsigned 8-bit integral (octet, or byte), commonly seen as `uint8_t` from _stdint.h_. |
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## Definitions
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This list defines the terms used across the entire set of XAP protocol documentation.
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| Name | Definition |
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| -- | -- |
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| _Capability_ | A way to determine if certain functionality is enabled in the firmware. Any _subsystem_ that provides build-time restriction of functionality must provide a _route_ for a _capabilities query_. |
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| _Handler_ | A piece of code that is executed when a specific _route_ is received. |
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| _Payload_ | Any received data appended to the _route_, which gets delivered to the _handler_ when received. |
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| _Response_ | The data sent back to the host during execution of a _handler_. |
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| _Route_ | A sequence of _IDs_ describing the route to invoke a _handler_. |
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| _Secure Route_ | A _route_ which has potentially destructive consequences, necessitating prior approval by the user before executing. |
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| _Subsystem_ | A high-level area of functionality within XAP. |
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| _Unlock sequence_ | A physical sequence initiated by the user to enable execution of _secure routes_. |
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| _Broadcast Header_ | Packet format for broadcast messages. Takes the format:<br>`token` - token<br>`u8` - type<br>`u8` - length |
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| _ID_ | A single octet / 8-bit byte, representing Subsystem or Route index. |
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| _Request Header_ | Packet format for inbound data. Takes the format:<br>`token` - token<br>`u8` - length |
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| _Response Flags_ | An `u8` containing the status of the request. |
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| _Response Header_ | Packet format for outbound data. Takes the format:<br>`token` - token<br>`response_flags` - flags<br>`u8` - length |
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| _Token_ | A `u16` associated with a specific request as well as its corresponding response. Valid token values are within the range `0x0100`-`0xFFFF`. |
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## Requests and Responses
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Communication generally follows a request/response pattern.
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Each request needs to include a _token_ -- this `u16` value prefixes each outbound request from the host application and its corresponding response.
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This allows response messages to be correlated with their request, even if multiple host applications are communicating with the firmware simultaneously.
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Host applications should randomly generate a token ID for **every** outbound request, unless using a reserved token defined below.
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To ensure host interoperability, valid token values are within the range `0x0100`-`0xFFFF`.
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This token is followed by a `u8` signifying the length of data in the request.
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Two token values are reserved: `0xFFFE` and `0xFFFF`:
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* `0xFFFE`: A message sent by a host application may use this token if no response is to be sent -- a "fire and forget" message.
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* `0xFFFF`: Signifies a "broadcast" message sent by the firmware without prompting from the host application. Broadcast messages are defined later in this document.
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Any request will generate at least one corresponding response, with the exception of messages using reserved tokens. Maximum total message length is 128 bytes due to RAM constraints.
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Response messages will always be prefixed by the originating request _token_, directly followed by that request's _response flags_, then the response payload length:
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| Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
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| -- | -- | -- | -- | -- | -- | -- | -- |
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| `-` | `-` | `-` | `-` | `-` | `-` | `SECURE_FAILURE` | `SUCCESS` |
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* Bit 1 (`SECURE_FAILURE`): When this bit is set, the requested _route_ was marked _secure_ but an _unlock sequence_ has not completed.
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* Bit 0 (`SUCCESS`): When this bit is set, the request was successfully handled. If not set, all payload data should be disregarded, and the request retried if appropriate (with a new token).
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### Example "conversation":
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**Request** -- version query:
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| Byte | 0 | 1 | 2 | 3 | 4 |
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| --- | --- | --- | --- | --- | --- |
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| **Purpose** | Token | Token | Payload Length | Route | Route |
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| **Value** | `0x43` | `0x2B` | `0x02` | `0x00` | `0x00` |
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**Response** -- matching token, successful flag, payload of `0x03170192` = 3.17.192:
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| Byte | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
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| --- | --- | --- | --- | --- | --- | --- | --- | --- |
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| **Purpose** | Token | Token | Response Flags | Payload Length | Payload | Payload | Payload | Payload |
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| **Value** | `0x43` | `0x2B` | `0x01` | `0x04` | `0x92` | `0x01` | `0x17` | `0x03` |
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## Routes
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Subsystem validity should be queried through the “Enabled-in-firmware subsystem query” under the QMK subsystem (route=0x00,0x01).
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This is the primary method for determining if a subsystem has been enabled in the running firmware.
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### XAP - `0x00`
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This subsystem is always present, and provides the ability to query information about the XAP protocol of the connected device.
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| Name | Route | Tags | Payloads | Description |
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| -- | -- | -- | -- | -- |
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| Version Query | `0x00 0x00` | | __Response:__ `u32` | XAP protocol version query.<br><br>* Returns the BCD-encoded version in the format of XX.YY.ZZZZ => `0xXXYYZZZZ`<br> * e.g. 3.2.115 will match `0x03020115`, or bytes {0x15,0x01,0x02,0x03}.|
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| Capabilities Query | `0x00 0x01` | | __Response:__ `u32` | XAP subsystem capabilities query. Each bit should be considered as a "usable" route within this subsystem.|
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| Enabled subsystem query | `0x00 0x02` | | __Response:__ `u32` | XAP protocol subsystem query. Each bit should be considered as a "usable" subsystem. For example, checking `(value & (1 << XAP_ROUTE_QMK) != 0)` means the QMK subsystem is enabled and available for querying.|
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| Secure Status | `0x00 0x03` | | __Response:__ `u8` | Query secure route status<br><br>* 0 means secure routes are disabled<br>* 1 means unlock sequence initiated but incomplete<br>* 2 means secure routes are allowed<br>* any other value should be interpreted as disabled|
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| Secure Unlock | `0x00 0x04` | | | Initiate secure route unlock sequence|
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| Secure Lock | `0x00 0x05` | | | Disable secure routes|
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### QMK - `0x01`
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This subsystem is always present, and provides the ability to address QMK-specific functionality.
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| Name | Route | Tags | Payloads | Description |
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| -- | -- | -- | -- | -- |
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| Version Query | `0x01 0x00` | | __Response:__ `u32` | QMK protocol version query.<br><br>* Returns the BCD-encoded version in the format of XX.YY.ZZZZ => `0xXXYYZZZZ`<br> * e.g. 3.2.115 will match `0x03020115`, or bytes {0x15,0x01,0x02,0x03}.|
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| Capabilities Query | `0x01 0x01` | | __Response:__ `u32` | QMK subsystem capabilities query. Each bit should be considered as a "usable" route within this subsystem.|
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| Board identifiers | `0x01 0x02` | | __Response:__<br> * Vendor ID: `u16`<br> * Product ID: `u16`<br> * Product Version: `u16`<br> * QMK Unique Identifier: `u32` | Retrieves the set of identifying information for the board.|
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| Board Manufacturer | `0x01 0x03` | | __Response:__ `string` | Retrieves the name of the manufacturer|
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| Product Name | `0x01 0x04` | | __Response:__ `string` | Retrieves the product name|
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| Config Blob Length | `0x01 0x05` | | __Response:__ `u16` | Retrieves the length of the configuration data bundled within the firmware|
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| Config Blob Chunk | `0x01 0x06` | | __Request:__ `u16`<br><br>__Response:__ `u8[32]` | Retrieves a chunk of the configuration data bundled within the firmware|
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| Jump to bootloader | `0x01 0x07` | __Secure__ | __Response:__ `u8` | Jump to bootloader<br><br>May not be present - if QMK capabilities query returns “true”, then jump to bootloader is supported<br><br>* 0 means secure routes are disabled, and should be considered as a failure<br>* 1 means successful, board will jump to bootloader|
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| Hardware Identifier | `0x01 0x08` | | __Response:__ `u32[4]` | Retrieves a unique identifier for the board.|
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| Reinitialize EEPROM | `0x01 0x09` | __Secure__ | __Response:__ `u8` | Reinitializes the keyboard's EEPROM (persistent memory)<br><br>May not be present - if QMK capabilities query returns “true”, then reinitialize is supported<br><br>* 0 means secure routes are disabled, and should be considered as a failure<br>* 1 means successful, board will reinitialize and then reboot|
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### Keyboard - `0x02`
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This subsystem is always present, and reserved for vendor-specific functionality. No routes are defined by XAP.
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### User - `0x03`
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This subsystem is always present, and reserved for user-specific functionality. No routes are defined by XAP.
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### Keymap - `0x04`
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This subsystem allows for query of currently configured keycodes.
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| Name | Route | Tags | Payloads | Description |
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| Capabilities Query | `0x04 0x01` | | __Response:__ `u32` | Keymap subsystem capabilities query. Each bit should be considered as a "usable" route within this subsystem.|
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| Get Layer Count | `0x04 0x02` | | __Response:__ `u8` | Query maximum number of layers that can be addressed within the keymap.|
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| Get Keycode | `0x04 0x03` | | __Request:__<br> * Layer: `u8`<br> * Row: `u8`<br> * Column: `u8`<br><br>__Response:__ `u16` | Query the Keycode at the requested location.|
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| Get Encoder Keycode | `0x04 0x04` | | __Request:__<br> * Layer: `u8`<br> * Encoder: `u8`<br> * Clockwise: `u8`<br><br>__Response:__ `u16` | Query the Keycode at the requested location.|
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### Remapping - `0x05`
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This subsystem allows for live reassignment of keycodes without rebuilding the firmware.
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| Name | Route | Tags | Payloads | Description |
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| Capabilities Query | `0x05 0x01` | | __Response:__ `u32` | Remapping subsystem capabilities query. Each bit should be considered as a "usable" route within this subsystem.|
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| Get Layer Count | `0x05 0x02` | | __Response:__ `u8` | Query maximum number of layers that can be addressed within the keymap.|
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| Set Keycode | `0x05 0x03` | __Secure__ | __Request:__<br> * Layer: `u8`<br> * Row: `u8`<br> * Column: `u8`<br> * Keycode: `u16` | Modify the Keycode at the requested location.|
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| Set Encoder Keycode | `0x05 0x04` | __Secure__ | __Request:__<br> * Layer: `u8`<br> * Encoder: `u8`<br> * Clockwise: `u8`<br> * Keycode: `u16` | Modify the Keycode at the requested location.|
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### Lighting - `0x06`
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This subsystem allows for control over the lighting subsystem.
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| Name | Route | Tags | Payloads | Description |
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| Capabilities Query | `0x06 0x01` | | __Response:__ `u32` | Lighting subsystem capabilities query. Each bit should be considered as a "usable" route within this subsystem.|
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## Broadcast messages
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Broadcast messages may be sent by the firmware to the host, without a corresponding inbound request. Each broadcast message uses the token `0xFFFF`, and does not expect a response from the host. Tokens are followed by an _ID_ signifying the type of broadcast, with corresponding _payload_.
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### Log message - `0x00`
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Replicates and replaces the same functionality as if using the standard QMK `CONSOLE_ENABLE = yes` in `rules.mk`. Normal prints within the firmware will manifest as log messages broadcast to the host. `hid_listen` will not be functional with XAP enabled.
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Log message payloads include a `u8` signifying the length of the text, followed by the `u8[Length]` containing the text itself.
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**Example Log Broadcast** -- log message "Hello QMK!"
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| Byte | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
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| **Purpose** | Token | Token | Broadcast Type | Length | Payload | Payload | Payload | Payload | Payload | Payload | Payload | Payload | Payload | Payload |
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| **Value** | `0xFF` | `0xFF` | `0x00` | `0x0A`(10) | `0x48`(H) | `0x65`(e) | `0x6C`(l) | `0x6C`(l) | `0x6F`(o) | `0x20`( ) | `0x51`(Q) | `0x4D`(M) | `0x4B`(K) | `0x21`(!) |
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### Secure Status - `0x01`
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Secure status has changed. Payloads include a `u8` matching a 'Secure Status' request.
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**Example Secure Status Broadcast** -- secure "Unlocking"
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| Byte | 0 | 1 | 2 | 3 |
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| --- | --- | --- | --- | --- |
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| **Purpose** | Token | Token | Broadcast Type | Secure Status |
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| **Value** | `0xFF` | `0xFF` | `0x01` | `0x01` |
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### Keyboard - `0x02`
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Reserved for vendor-specific functionality. No messages are defined by XAP.
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### User - `0x03`
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Reserved for user-specific functionality. No messages are defined by XAP.
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