# Data Transfer Fix - AudioCoder

## Problem Identified
The GUI would show "CLOCK LOCK pattern=AA" repeatedly but never receive any data. The decoder got stuck in the RX_SEARCH state.

## Root Cause Analysis

### Critical Bug #1: Missing syncBytes Declaration (PRIMARY)
**File:** `decoder.c` / `decoder.h`
**Issue:** The `try_phase_search()` function compares decoded symbols against `syncBytes[]`:
```c
if (byte != syncBytes[i])  // Line 177
    break;
```

However, `syncBytes` was only defined in `encoder.c` and **NOT** declared as `extern` in `decoder.h`. This meant:
- The decoder could not access the sync bytes array
- Phase search was comparing against uninitialized memory or garbage values
- Sync bytes would NEVER match
- Decoder would never transition from RX_SEARCH to RX_LOCKED
- No data would ever be received

**Fix Applied:**
Added to `decoder.h`:
```c
extern const uint8_t syncBytes[4];
```

### Critical Bug #2: State Machine Deadlock (SECONDARY)
**File:** `decoder.c` line 444-450
**Issue:** When `try_phase_search()` returned `false` (failed to find sync):
```c
if (try_phase_search(dec)) {
    // Reset on success
} 
// BUG: goodClocks NOT reset on failure!
```

This caused:
- `goodClocks` remained >= 8
- Every symbol period, state machine would try phase search again
- Infinite loop of failed phase searches
- CPU spinning without progress

**Fix Applied:**
Added reset on failure:
```c
} else {
    // Phase search failed, reset and try again
    dec->goodClocks = 0;
    dec->clockHistory = 0;
    dec->clockCount = 0;
}
```

### Enhancement #3: Debug Visibility
**File:** `decoder.c` line 193-194
**Issue:** No feedback when phase search fails

**Fix Applied:**
Added diagnostic output:
```c
printf("PHASE SEARCH FAILED bestScore=%d (need %zu)\n", bestScore, sizeof(syncBytes));
```

This shows:
- How many sync bytes matched (0-4)
- How many are needed (4)
- Helps diagnose frequency/timing mismatches

## How It Should Work Now

1. **Encoder Sends:**
   - Preamble (128 clock cycles)
   - Sync bytes: 'B' (0x42), 'R' (0x52), 'N' (0x4E), 'Q' (0x51)
   - Data payload

2. **Decoder Receives:**
   - RX_SEARCH: Listen for alternating clock pattern (0xAA alternating)
   - When found: goodClocks = 8
   - searchOffset increments, triggers phase search after 4 clock detections
   - Phase search: Find exact alignment of the 4 sync bytes
   - If found: RX_LOCKED state
   - RX_LOCKED: Decode symbols into data buffer

3. **Success Indicators:**
   - `CLOCK LOCK pattern=AA` (multiple times)
   - `PHASE SEARCH FAILED bestScore=3 or 4` (diagnosing alignment)
   - `SYNC ALIGN phase=XXX score=4` (SUCCESS - decoder locked)
   - `DATA XXXXXXXX` (receiving data bytes)

## Testing
The binary has been rebuilt with all fixes applied. Expected output should progress from CLOCK LOCK → PHASE SEARCH FAILED (or SUCCEED) → SYNC ALIGN → DATA.