# Ausiomixer HID Protocol

VID=`0x2E8A` PID=`0xA541`  
Composite USB: **CDC** (debug printf) + **HID** (mixer reports), vendor usage page `0xFF00`.

## Input report (Pico → Host) — 8 bytes

| Offset | Field |
|--------|-------|
| 0 | `report_id = 1` |
| 1 | `enc1_delta` (int8) — scroll selection |
| 2 | `enc2_delta` (int8) — selected session volume steps |
| 3 | flags: bit0=E1 SW, bit1=E2 SW |
| 4 | pot `0..100` — system master |
| 5..7 | reserved |

## Output report (Host → Pico) — 64 bytes

| Offset | Field |
|--------|-------|
| 0 | `report_id = 2` |
| 1 | `session_count` |
| 2 | `selected_index` |
| 3 | `master_vol` `0..100` |
| 4 | `page_start` |
| 5 | `n_visible` (`0..5`) |
| 6.. | slots × `n_visible` |

Each slot (11 bytes): `vol` (1) + UTF-8 name (9) + `NUL` (1).

## Controls

| Hardware | Action |
|----------|--------|
| Encoder 1 | Change selected session |
| Encoder 2 | Change volume of selected session (±2% per click on host) |
| Pot GP26 | Absolute master volume |
| SW | Logged (E1/E2); reserved |

## Run

1. Flash `build/ausiomixer.uf2`
2. `dotnet run --project host/Ausiomixer.Host`
3. Play audio in Windows; names appear on the ILI9341 (320×240)