OpenLogi0x4220 · LockKeyState
Read the Num Lock, Caps Lock, and Scroll Lock state, or decode an unsolicited lock-key report.
LockKeyState reports the engaged lock keys on keyboards that expose feature 0x4220. OpenLogi reads the state and uses later broadcasts for lock-key notices.
Spec: No public Logitech specification. Layout reverse-engineered from Logi Options+ 2.8 (static analysis). Used by: Lock-key notices.
Function reference
LockKeyStateFeature is creatable for feature version 0.
Methods
| Function | HID++ fn | Signature | Returns |
|---|---|---|---|
get_lock_state | 0 | () | LockKeys |
decode_broadcast | event decoder | (&[u8; 16]) | LockKeys |
get_lock_state is async and returns Result<LockKeys, Hidpp20Error>. decode_broadcast is an infallible associated function.
Types
LockKeys
LockKeys is a retained u8 bitfield. OpenLogi keeps unnamed bits rather than rejecting a newer keyboard state.
| Field | Bit | Description |
|---|---|---|
NUM_LOCK | 1 << 0 | Num Lock is engaged. |
CAPS_LOCK | 1 << 1 | Caps Lock is engaged. |
SCROLL_LOCK | 1 << 2 | Scroll Lock is engaged. |
Events
OpenLogi has no listen() method for this feature. The inventory path filters software ID 0, then calls decode_broadcast for reports at this feature index.
| Event | Payload | Description |
|---|---|---|
| Lock-key state | LockKeys | The complete current lock-key bitmap. |
Wire format
get_lock_state uses a 3-byte short request payload. OpenLogi normalizes its reply to 16 bytes before decoding byte 0.
get_lock_state (fn 0)
Request:
| Byte | Field | Notes |
|---|---|---|
| 0–2 | — | No parameters. OpenLogi sends 0x00, 0x00, 0x00. |
Response:
| Byte | Field | Notes |
|---|---|---|
| 0 | lock_keys | LockKeys bitmap. |
| 1–15 | — | OpenLogi ignores these bytes. |
Lock-key broadcast
Logi Options+ 2.8 reads byte 0 from any unsolicited report on this feature. OpenLogi follows that rule and does not validate the report function.
| Byte | Field | Notes |
|---|---|---|
| 0 | lock_keys | Same LockKeys bitmap as get_lock_state. Options+ 2.8 |
| 1–15 | — | OpenLogi ignores these bytes. |
How OpenLogi uses it
Since v0.8.15, OpenLogi reads the lock state once per online connection. That baseline lets it identify each named bit that changed in a later broadcast.
OpenLogi queues one notice update for each changed named key. It does not reconcile inventory or increase a settings revision for these transient states.
The agent honors lock_key_notifications, which defaults to true. It shows Caps Lock on macOS, Linux, and Windows, but Num Lock and Scroll Lock only on Linux and Windows.
OpenLogi does not write 0x4220 or restore state at exit. See On-screen notices for the visible behavior.
Usage (Rust)
use hidpp::{
device::Device,
feature::lock_key_state::{LockKeyStateFeature, LockKeys},
};
// `device` is a discovered HID++ device.
device.enumerate_features().await?;
if let Some(feature) = device.get_feature::<LockKeyStateFeature>() {
let keys = feature.get_lock_state().await?;
if keys.contains(LockKeys::CAPS_LOCK) {
println!("Caps Lock is on");
}
}