XMOS EQ HID Communication Protocol Specification¶
Protocol Overview ¶
Functional Scope and Purpose
This document provides detailed specifications for the communication protocol between XMOS EQ HID devices and PC-based GUI software. The protocol offers a complete feature set for EQ mode control, parameter configuration, and device information retrieval.
1. Protocol Foundation Specification ¶
1.1 Underlying Communication Protocol¶
Based on USB HID (Human Interface Device) Protocol
| Parameter | Value |
|---|---|
| Transmission Method | USB HID |
| Data Packet Size | 64 bytes (including 1-byte Report ID 0x01) |
| Effective Data | 63 bytes |
| Byte Order | Little Endian |
| Sync Header | 0x77 (fixed at byte 1, Report ID at byte 0) |
1.2 HID Device Identification¶
| Parameter | Value | Description |
|---|---|---|
| Usage Page | 0xff82 or 0xff83 | HID device type identifier |
| Report ID | 0x01 | First byte (byte 0) when sending |
| Transmission Mode | Non-blocking mode | Prevents GUI freezing |
1.3 Communication Mechanism¶
Data Transmission Notes
- All data is transmitted in Little Endian byte order
- Sync header 0x77 is fixed at byte 1 (byte 0 is Report ID = 0x01)
- Recommend minimum 5ms interval between commands to avoid device processing delays
2. Protocol Command Set ¶
2.1 Command Classification Overview¶
Command Usage Instructions
- All commands must include Report ID 0x01 (byte 0) and sync header 0x77 (byte 1)
- Total packet length is fixed at 64 bytes (including Report ID)
- Unused bytes must be padded with 0
2.1.1 Command Header Definitions¶
| Command Header | Command Name | Function Description | Direction |
|---|---|---|---|
| 0x8A | SET_EQ_MODE | Switch current EQ mode | PC → Device |
| 0x8B | GET_EQ_MODE | Get current EQ mode information (mode number, gain, name) | PC → Device |
| 0x8C | SET_MODE_GAIN_AND_NAME | Set overall gain and name for specified mode | PC → Device |
| 0x8D | SET_EQ_PARAMS | Send single filter parameters | PC → Device |
| 0x8E | GET_EQ_PARAMS | Read single filter parameters | PC ↔ Device |
| 0x8F | GET_DEVICE_INFO | Get basic device information (PID/VID/SN) | PC ↔ Device |
| 0x90 | RESET_EQ_PARAMS | Reset EQ parameters (restore presets) | PC ↔ Device |
2.2 Detailed Command Formats¶
2.2.1 Switch EQ Mode (0x8A)¶
Function: Switch current EQ mode
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8A |
| 3 | 1 | mode | Mode value (0-5: presets, 6-8: user, 9: Bypass) |
| 4-63 | 60 | reserved | Reserved fields (fill with 0) |
2.2.2 Get Current EQ Mode Information (0x8B)¶
Function: Get current mode value, overall gain, and mode name
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8B |
| 3-63 | 61 | reserved | Reserved fields (fill with 0) |
Response Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8B (echo) |
| 3 | 1 | mode | Current mode value |
| 4-7 | 4 | gain | Overall gain (int32, little endian, range -50dB ~ 0dB) |
| 8-23 | 16 | name | Mode name (UTF-8 string) |
| 24-63 | 40 | reserved | Reserved fields (fill with 0) |
2.2.3 Set Mode Overall Gain and Name (0x8C)¶
Function: Set overall gain and name for target mode
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8C |
| 3 | 1 | mode | Target mode value (0-9) |
| 4-7 | 4 | gain | Overall gain (int32, little endian) |
| 8-23 | 16 | name | Mode name (UTF-8 string) |
| 24-63 | 40 | reserved | Reserved fields (fill with 0) |
2.2.4 Set EQ Parameters (0x8D)¶
Function: Send single filter parameters
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8D |
| 3 | 1 | mode | Mode value (0-9) |
| 4 | 1 | band | Filter index (0-7) |
| 5 | 1 | type | Filter type code |
| 6-9 | 4 | freq | Center frequency Hz (float, little endian) |
| 10-13 | 4 | q | Q value (float, little endian) |
| 14-17 | 4 | bw | Bandwidth Hz (float, little endian) |
| 18-21 | 4 | gain | Gain dB (float, little endian) |
| 22-63 | 42 | reserved | Reserved fields (fill with 0) |
Filter Type Codes:
| Code | Type | Code | Type |
|---|---|---|---|
| 0x00 | Bypass | 0x06 | Band Reject |
| 0x01 | All Pass | 0x07 | Notch |
| 0x02 | Peak | 0x08 | Constant Q |
| 0x03 | Low Pass | 0x09 | Low Shelf |
| 0x04 | High Pass | 0x0A | High Shelf |
| 0x05 | Band Pass |
Data Format Notes:
Floating Point and Byte Order
- All floating-point numbers follow IEEE 754 float standard with little endian byte order
- All multi-byte integers use Little Endian byte order
2.2.5 Read EQ Parameters (0x8E)¶
Function: Read parameters of specified filter
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8E |
| 3 | 1 | mode | Mode value (0-9) |
| 4 | 1 | band | Filter index (0-7) |
| 5-63 | 59 | reserved | Reserved fields (fill with 0) |
Response Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8E (echo) |
| 3 | 1 | mode | Mode value |
| 4 | 1 | band | Filter index |
| 5 | 1 | type | Filter type code |
| 6-9 | 4 | freq | Center frequency Hz (float, little endian) |
| 10-13 | 4 | q | Q value (float, little endian) |
| 14-17 | 4 | bw | Bandwidth Hz (float, little endian) |
| 18-21 | 4 | gain | Gain dB (float, little endian) |
| 22-63 | 41 | reserved | Reserved fields (fill with 0) |
2.2.6 Get Device Information (0x8F)¶
Function: Get basic device identification information
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8F |
| 3-63 | 61 | reserved | Reserved fields (fill with 0) |
Response Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x8F (echo) |
| 3-4 | 2 | pid | Product ID (uint16, little endian) |
| 5-6 | 2 | vid | Vendor ID (uint16, little endian) |
| 7-22 | 16 | product | Product string (UTF-8) |
| 23-38 | 16 | vendor | Vendor string (UTF-8) |
| 39-54 | 16 | sn | Serial number string (UTF-8) |
| 55-63 | 9 | reserved | Reserved fields (fill with 0) |
2.2.7 Reset EQ Parameters (0x90)¶
Function: Reset EQ parameters for specified mode or all modes
Request Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x90 |
| 3 | 1 | mode | Mode number (0-9, 0xFF = reset all modes) |
| 4-63 | 60 | reserved | Reserved fields (fill with 0) |
Response Format (64 bytes):
| Offset | Length | Field Name | Description |
|---|---|---|---|
| 0 | 1 | report_id | Fixed value: 0x01 |
| 1 | 1 | sync_header | Sync header: 0x77 |
| 2 | 1 | cmd_header | Command header: 0x90 (echo) |
| 3 | 1 | status | Status code (0x00=success, 0x01=failure) |
| 4-63 | 60 | reserved | Reserved fields (fill with 0) |
3. Data Flow and Timing ¶
3.1 Typical Operation Flows¶
3.1.1 Mode Switching Flow¶
- GUI sends SET_EQ_MODE command (0x8A)
- Device updates internal mode state
- GUI sends GET_EQ_MODE command (0x8B) for confirmation
- Device responds with current mode state
3.1.2 Parameter Setting Flow¶
- GUI sends SET_EQ_MODE command to switch to target mode (0x8A)
- Send commands for all 8 filters sequentially (0x8D)
- Device receives and updates internal parameter cache
- Optional: Send GET_EQ_PARAMS command to verify parameters (0x8E)
3.1.3 Parameter Reading Flow¶
- GUI sends SET_EQ_MODE command to switch to target mode (0x8A)
- GUI sends GET_EQ_PARAMS request (0x8E)
- Device prepares response data
- GUI reads response
3.2 Timing Requirements and Constraints¶
Timing Requirements
- Command Interval: Minimum 5ms recommended
- Read Delay: Wait 100ms after sending read request
- Mode Switching: Wait for device internal state to stabilize after completion
Protocol Limitations and Constraints
Hardware Limitations
- Filter Count: Fixed at 8 filters (MAX_EQ_BANDS = 8)
- Mode Count: 0-5 are preset modes, 6-8 are user modes, 9 is Bypass mode
- Sample Rate Support: 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz, 192kHz (device capability, independent of protocol fields)
Parameter Ranges
| Parameter | Range | Format |
|---|---|---|
| Center frequency (freq) | 20Hz - 20kHz | float (little endian) |
| Q value (q) | 0.1 - 30.0 | float (little endian) |
| Bandwidth (bw) | 1Hz - 20kHz | float (little endian) |
| Gain (gain) | -24dB - +24dB | float (little endian) |
| Overall gain (mode gain) | -50dB - 0dB | int32 (little endian) |
4. Preset Mode Definitions ¶
4.1 Mode Classification¶
| Mode Index | Mode Name | Description | Type |
|---|---|---|---|
| 0 | Flat/Linear | Flat response, no EQ processing | Preset Mode |
| 1 | Pop/Rock | Optimized for pop/rock music | Preset Mode |
| 2 | Classical | Optimized for classical music | Preset Mode |
| 3 | Jazz | Optimized for jazz music | Preset Mode |
| 4 | Vocal | Vocal enhancement | Preset Mode |
| 5 | Bass Boost | Bass enhancement | Preset Mode |
| 6 | User 1 | User-defined mode 1 | User Mode |
| 7 | User 2 | User-defined mode 2 | User Mode |
| 8 | User 3 | User-defined mode 3 | User Mode |
| 9 | Bypass | EQ function bypass | Special Mode |
Mode Characteristics
- Preset Modes: Factory presets, non-modifiable, optimized for specific music genres
- User Modes: Support user-defined parameters, can be saved and reset
- Bypass Mode: Completely disables EQ processing, audio signal passes through (Bypass)
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