0x1814 · changeHost – OpenLogi Docs

查询多主机设备的槽位数量并切换当前连接，同时支持每槽 cookie 管理以实现增强型连接失败回退。

多主机设备通过此功能查询支持的主机槽位 / RF 频道数量并在它们之间切换。get_host_info 返回一个 ChangeHostInfo 结构体，包含主机数量、当前主机索引以及 ChangeHostCapabilities 标志位字段；set_current_host 发送一个"发送即忘"的切换请求——设备在主机切换时通常会重置连接，因此不等待响应。

另有两个函数管理每个主机槽位的cookie 字节——设备非易失性存储中的一个小数值。get_cookies 返回每个槽位对应的一字节 cookie；set_cookie 写入单个条目。固件在新主机配对到该槽位时会清除其 cookie。增强型主机切换（ENHANCED_HOST_SWITCH 能力标志）利用非零 cookie 在连接失败时选择备用主机，之后再返回原始槽位。

ChangeHostInfo —— host_count、current_host、capabilities。
ChangeHostCapabilities::ENHANCED_HOST_SWITCH —— 连接失败时先回退到 cookie 非零的主机，再返回原始主机。

规格： Logitech HID++ 2.0 —— changeHost。用于： openlogi-hidpp 中的类型化封装。

Function reference

The ChangeHostFeature wrapper (0x1814) exposes methods for querying and changing the active host slot on multi-host devices, plus per-slot cookie management.

Methods

Function	HID++ fn	Signature	Returns
`get_host_info`	0	`()`	`ChangeHostInfo`
`set_current_host`	1	`(host: u8)`	`()`
`get_cookies`	2	`(host_count: u8)`	`Vec<u8>`
`set_cookie`	3	`(host: u8, cookie: u8)`	`()`

All methods are async and return Result<…, Hidpp20Error>.

Types

`ChangeHostInfo`

Host configuration returned by get_host_info.

Field	Type	Description
`host_count`	`u8`	Number of hosts / RF channels.
`current_host`	`u8`	Current host index, in `0..host_count`.
`capabilities`	`ChangeHostCapabilities`	Host-switching capabilities.

`ChangeHostCapabilities`

Host-switching capabilities bitflags reported by get_host_info.

Flag	Bit/Value	Description
`ENHANCED_HOST_SWITCH`	`1 << 0`	Enhanced host switching is enabled: on a failed connection the device falls back to another host with a non-zero cookie before returning to the original host.

Wire format

Short 3-byte request payloads are used for all functions; responses are read from the 16-byte long payload via extend_payload().

`get_host_info` (fn 0)

Request: [0x00, 0x00, 0x00] (no parameters)

Response (byte → field):

Byte	Field	Notes
0	`host_count`	Total number of host slots / RF channels
1	`current_host`	Active host index, zero-based
2	`capabilities`	`ChangeHostCapabilities` bitflags; bit 0 = `ENHANCED_HOST_SWITCH`

`set_current_host` (fn 1)

Sent as a notify (fire-and-forget); no response is read.

Request: [host, 0x00, 0x00]

Byte	Field	Notes
0	`host`	Target host index to activate
1–2	—	Padding, always `0x00`

`get_cookies` (fn 2)

Request: [0x00, 0x00, 0x00] (no parameters)

Response: bytes payload[0..host_count] — one cookie byte per host slot in order. The caller supplies host_count (from get_host_info) to slice the response; bytes beyond host_count are ignored.

Byte	Field	Notes
0	cookie for host 0
1	cookie for host 1
…	cookie for host N-1	Up to `host_count` bytes

`set_cookie` (fn 3)

Request: [host, cookie, 0x00]

Byte	Field	Notes
0	`host`	Host slot index whose cookie is being written
1	`cookie`	Arbitrary byte value to store in NVM
2	—	Padding, always `0x00`

The device ACK response is awaited but its payload is discarded.

Usage (Rust)

use hidpp::feature::change_host::ChangeHostFeature;

// device: &mut Device, already created via Device::new(channel, index)
device.enumerate_features().await?;
if let Some(feat) = device.get_feature::<ChangeHostFeature>() {
    // Query host count, current host, and capabilities
    let info = feat.get_host_info().await?;
    println!("hosts: {}, current: {}", info.host_count, info.current_host);

    // Read the per-host cookies (one byte per slot)
    let cookies = feat.get_cookies(info.host_count).await?;
    println!("cookies: {:?}", cookies);

    // Switch to host 1 (fire-and-forget; device will reset its connection)
    feat.set_current_host(1).await?;
}

0x1814 · changeHost

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