HID Protocol Reference¶

The Lexcelon Slicky-1.0 is a USB HID device that supports bidirectional vendor-specific HID communication for controlling its LED color and querying device state.

Device Identification¶

Field	Value
Vendor ID	`0x04D8` (Microchip Technology)
Product ID	`0xEC24`
Manufacturer	Lexcelon
Product	Slicky-1.0

Command Summary¶

All commands use a 65-byte buffer: report ID (0x00) + 64-byte payload. The command byte is at offset 1.

CMD	Name	Direction	Description
`0x00`	Device Info	Host → Device → Host	Query hardware/firmware version
`0x01`	Serial	Host → Device → Host	Query device serial number
`0x0A`	Set Color	Host → Device	Set the LED to a specific RGB color
`0x0B`	Get Color	Host → Device → Host	Read the current LED color

CMD 0x0A — Set Color¶

Request (65 bytes)¶

Index: [0]   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]   [9..64]
Value: 0x00  0x0A  0x04  0x00  0x00  0x00  BLUE  GRN   RED   0x00...
       ^^^^  ^^^^  ^^^^                    ^^^^  ^^^^  ^^^^
       rpt   cmd   sub                     B     G     R
       ID

Offset	Size	Description
0	1	Report ID — always `0x00`
1	1	Command — `0x0A` (set color)
2	1	Subcommand — `0x04`
3–5	3	Reserved — `0x00`
6	1	Blue channel (0–255)
7	1	Green channel (0–255)
8	1	Red channel (0–255)
9–64	56	Padding — `0x00`

BGR byte order: The color bytes are in BGR order, not RGB. Blue is at index 6, green at 7, red at 8.

Turn Off¶

To turn the light off, send a set-color report with R=0, G=0, B=0. The command and subcommand bytes remain the same.

CMD 0x0B — Get Color¶

Reads the current LED color from the device.

Request (65 bytes)¶

Index: [0]   [1]   [2..64]
Value: 0x00  0x0B  0x00...
       ^^^^  ^^^^
       rpt   cmd
       ID

Response (64 bytes, read via HID input report)¶

Index: [0]   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8..63]
Value: 0x0B  0x04  0x00  0x00  0x00  BLUE  GRN   RED   0x00...
       ^^^^  ^^^^                    ^^^^  ^^^^  ^^^^
       cmd   sub                     B     G     R

Offset	Size	Description
0	1	Command echo — `0x0B`
1	1	Subcommand — `0x04`
2–4	3	Reserved — `0x00`
5	1	Blue channel (0–255)
6	1	Green channel (0–255)
7	1	Red channel (0–255)
8–63	56	Padding — `0x00`

A read timeout of 200ms is used. The response color bytes are also in BGR order, at offsets 5-7 (shifted by one compared to the set-color command since there is no report ID byte in the input report).

CMD 0x00 — Device Info¶

Queries hardware and firmware version information.

Request (65 bytes)¶

Index: [0]   [1]   [2..64]
Value: 0x00  0x00  0x00...
       ^^^^  ^^^^
       rpt   cmd
       ID

Response (64 bytes)¶

Index: [0]   [1]   [2]   [3]   [4]   [5]   [6..63]
Value: 0x00  0x02  0x00  0x00  0x02  0x01  0x00...
       ^^^^  ^^^^              ^^^^  ^^^^
       cmd   len?              fw?   fw?

The exact interpretation of the response fields beyond the command echo byte is not fully documented. The observed values suggest firmware version information.

CMD 0x01 — Serial Query¶

Queries the device serial number.

Request (65 bytes)¶

Index: [0]   [1]   [2..64]
Value: 0x00  0x01  0x00...
       ^^^^  ^^^^
       rpt   cmd
       ID

Response (64 bytes)¶

Index: [0]   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8..63]
Value: 0x01  0x04  0x00  0x00  0x77  0x79  0x71  0x99  0x00...
       ^^^^  ^^^^              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       cmd   len?              serial (BCD-encoded digits)

The serial number bytes at offsets 4-7 contain BCD-encoded digits. For example, 0x77 0x79 0x71 0x99 decodes to serial "77971799".

HID Report Descriptor¶

The device declares a 33-byte HID report descriptor using vendor-specific usage page 0xFF00:

Report Type	Size
Input	64 bytes
Output	64 bytes
Feature	1 byte

Commands are sent as Output reports (65 bytes including report ID). Responses are read as Input reports (64 bytes, no report ID prefix).

Button Behavior¶

The Slicky-1.0 has a physical button that cycles through a fixed color sequence:

Cycle order: Custom color → White → Red → Yellow → Green → Off → White → Red → ...

The button cycling is handled entirely in firmware
The button does not generate HID input reports
CMD 0x0B does reflect the button-cycled color (confirmed experimentally)

Button Color → Status Mapping¶

Button Color	Hex	Status Preset
White	`#FFFFFF`	In Meeting
Red	`#FF0000`	Busy
Yellow	`#FFFF00`	Away
Green	`#00FF00`	Available
Off	`#000000`	Off (clear status)

All button-cycle colors use pure channel values (0x00 or 0xFF), enabling exact-match detection. The daemon polls CMD 0x0B every 2 seconds to detect button presses and can optionally sync the detected status to Slack.

Communication Pattern¶

Bidirectional: The host sends output reports and reads input reports for query responses
Stateless: Each command is independent. No handshake or session required
Single report: One 65-byte write per command, one 64-byte read per response
Read timeout: Use a 200ms timeout when reading responses; not all commands may produce a response on all firmware versions

Constants¶

pub const VENDOR_ID: u16 = 0x04D8;
pub const PRODUCT_ID: u16 = 0xEC24;
pub const REPORT_SIZE: usize = 64;       // HID report payload
pub const BUFFER_SIZE: usize = 65;       // report ID + payload
pub const READ_TIMEOUT_MS: i32 = 200;    // read timeout for responses

Reverse Engineering Notes¶

The protocol was reverse-engineered in two phases:

Phase 1 (write commands): USB traffic capture from the original Lexcelon desktop application using Wireshark with USBPcap. Discovered CMD 0x0A set-color with BGR byte order.
Phase 2 (read commands): Systematic probing of all 256 command bytes using tools/slicky-probe. Discovered CMD 0x00 (device info), CMD 0x01 (serial), and CMD 0x0B (color readback). Most command bytes produce no response.