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[]:

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:

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):

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:

} 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:

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

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

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