HID++ Feature Codes for DPI, SmartShift, Scroll, and Lighting in OpenLogi

OpenLogi uses HID++ feature codes 0x2201 and 0x2202 for DPI configuration, 0x2110 and 0x2111 for SmartShift and scroll wheel modes, and 0x1000 for per-key lighting control, all registered in the openlogi-hidpp crate.

The AprilNEA/OpenLogi project implements a Rust-based driver stack for Logitech HID++ devices. Understanding the specific HID++ feature codes that map hardware capabilities—such as sensor resolution, wheel ratcheting, and RGB illumination—to protocol commands is essential for extending device support or debugging communication layers.

DPI Control via Feature Codes 0x2201 and 0x2202

OpenLogi distinguishes between legacy and extended DPI configuration using two separate feature identifiers.

Adjustable DPI (0x2201) and Extended DPI (0x2202)

In crates/openlogi-hidpp/src/feature/registry.rs, the registry maps 0x2201 to AdjustableDpiFeature and 0x2202 to ExtendedDpiFeature. These structs handle reading and writing sensor resolution values, DPI ranges, lift-off distance, and DPI-LED status.

Control IDs for DPI Operations

The reprog_controls/control_ids.rs file defines low-level control IDs used within these features:

• DPI_CHANGE = 0xED
• DPI_SWITCH = 0xFD

These constants appear in lines 170–219 of the control IDs module and are referenced by the DPI write implementation in crates/openlogi-device/src/write/dpi.rs.

SmartShift and Scroll Wheel Control (0x2110 and 0x2111)

SmartShift functionality—toggling between freespin and ratchet scroll modes—uses dedicated feature codes that also encode the scroll wheel's operational state.

SmartShift Wheel (0x2110) and Enhanced (0x2111)

The registry associates 0x2110 with SmartShiftFeature and 0x2111 with SmartShiftEnhancedFeature. The enhanced variant supports additional torque tuning and configurable auto-disengage thresholds, while the base feature handles basic mode switching.

Scroll Mode Encoding

According to crates/openlogi-device/src/write/smartshift.rs (lines 84–95), the WheelMode enum converts between the hardware's scroll mode state and the SmartShift feature status. This effectively embeds scroll control within the SmartShift feature implementation, meaning the scroll wheel mode is not a separate HID++ feature code but rather a data field within the 0x2110/0x2111 feature reports.

Lighting Control via Feature Code 0x1000

Per-key RGB lighting is managed through a distinct feature namespace separate from input controls.

Per-Key Lighting Implementation

The per_key_lighting.rs file implements the 0x1000 feature code for per-key lighting. This feature utilizes Report ID 0x12 to transmit 64-byte color data buffers, enabling configuration of solid colors, individual key RGB values, and lighting persistence settings across device power cycles.

Practical Implementation Examples

The following Rust snippets demonstrate how OpenLogi's internal API interacts with these HID++ feature codes.

Reading and Writing DPI

This example queries the current resolution using feature 0x2201 or 0x2202 and sets a new value:

use openlogi_core::hid::dpi::Dpi;

// Query current DPI (internally selects feature 0x2201 or 0x2202)
let dpi = client.get_dpi(route).await?;
println!("Current DPI: {}", dpi.current());

// Update sensor resolution (writes to the detected DPI feature)
client.set_dpi(route, Dpi::new(1200)).await?;

Configuring SmartShift Modes

This snippet toggles SmartShift using feature 0x2110 or 0x2111 and configures the ratchet threshold:

use openlogi_core::hid::smartshift::{
    SmartShiftMode, SmartShiftStatus, SmartShiftAutoDisengage, SmartShiftThreshold, TunableTorque,
};

// Toggle between freespin and ratchet (uses feature 0x2110/0x2111)
let mode = client.toggle_smartshift(route).await?;
println!("SmartShift mode: {:?}", mode);

// Apply specific ratchet settings with torque control
let status = SmartShiftStatus {
    mode: SmartShiftMode::Ratchet,
    auto_disengage: SmartShiftAutoDisengage::Threshold(
        SmartShiftThreshold::try_new(16).unwrap(),
    ),
    tunable_torque: Some(TunableTorque::try_new(60).unwrap()),
};
client.set_smartshift(route, status).await?;

Setting Per-Key Lighting

This example configures solid red lighting using feature 0x1000 and report 0x12:

use openlogi_core::hid::lighting::{Lighting, Color};

// Construct lighting configuration
let lighting = Lighting {
    enabled: true,
    color: Color::rgb(0xFF, 0x00, 0x00),
    brightness: 100,
    ..Default::default()
};

// Transmit via feature 0x1000 (report 0x12)
client.set_lighting(route, lighting).await?;

Summary

• DPI Management: OpenLogi uses feature codes 0x2201 (Adjustable DPI) and 0x2202 (Extended DPI) to handle sensor resolution, with internal control IDs 0xED and 0xFD defined in control_ids.rs.
• SmartShift and Scroll: Feature codes 0x2110 (SmartShift) and 0x2111 (SmartShift Enhanced) control freespin/ratchet behavior; scroll wheel mode state is encoded within these feature reports via the WheelMode enum in smartshift.rs.
• Lighting Control: Feature code 0x1000 manages per-key RGB lighting, utilizing Report ID 0x12 for 64-byte color data payloads defined in per_key_lighting.rs.
• Registry Location: All feature code mappings are centralized in crates/openlogi-hidpp/src/feature/registry.rs, which instantiates the appropriate feature structs based on device capability advertisements.

Frequently Asked Questions

What is the difference between feature code 0x2201 and 0x2202 in OpenLogi?

Code 0x2201 implements the legacy Adjustable DPI feature for basic sensor resolution control, while 0x2202 implements Extended DPI, which supports higher resolution tables and additional lift-off distance configuration. The registry.rs file maps these codes to AdjustableDpiFeature and ExtendedDpiFeature structs respectively, and the implementation in dpi.rs selects the appropriate feature based on the device's advertised capabilities.

How does OpenLogi handle scroll wheel mode changes via HID++?

OpenLogi maps scroll wheel modes (freespin versus ratchet) to the SmartShift feature codes 0x2110 and 0x2111. The conversion logic resides in crates/openlogi-device/src/write/smartshift.rs, where the WheelMode enum translates between raw HID++ status bytes and the internal SmartShift state, allowing scroll mode control without a separate dedicated feature code.

Which HID++ feature code controls per-key RGB lighting in OpenLogi?

The feature code 0x1000 controls per-key lighting functionality. This feature uses Report ID 0x12 to transmit 64-byte color buffers to the device, as implemented in crates/openlogi-hidpp/src/feature/per_key_lighting.rs. This separation allows lighting configuration to operate independently of input feature codes like DPI or SmartShift.

Where are the DPI control constants defined in the OpenLogi source code?

DPI-specific control constants such as DPI_CHANGE = 0xED and DPI_SWITCH = 0xFD are defined in crates/openlogi-hidpp/src/feature/reprog_controls/control_ids.rs within lines 170–219. The high-level feature code registry that maps 0x2201 and 0x2202 to their respective implementation structs is located in crates/openlogi-hidpp/src/feature/registry.rs.

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