74 lines
2.5 KiB
Python
74 lines
2.5 KiB
Python
"""Trace Tran sample-by-sample to find exactly where the codec drifts."""
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from __future__ import annotations
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import sys
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from pathlib import Path
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REPO = Path(__file__).resolve().parents[1]
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sys.path.insert(0, str(REPO))
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from analysis_idf.recon import TARGET, TXT, load_sidecar_samples
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def s4(n: int) -> int:
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return n if n < 8 else n - 16
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def i8(b: int) -> int:
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return b if b < 128 else b - 256
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def main():
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buf = TARGET.read_bytes()
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sc = load_sidecar_samples(TXT)
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GEO_LSB = 0.0003
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sc_tran = [int(round(v / GEO_LSB)) for v in sc["Tran"]]
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body = buf[0x0f1f:]
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# Tran[0], Tran[1] from preamble
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t0 = int.from_bytes(body[3:5], "big", signed=True)
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t1 = int.from_bytes(body[5:7], "big", signed=True)
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print(f"preamble Tran[0]={t0} Tran[1]={t1} (sidecar: {sc_tran[0]}, {sc_tran[1]})")
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# Block 0: 10 f8 at body[7:9]
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print(f"block 0: tag {body[7]:02x} {body[8]:02x}")
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print(f" block 0 first 10 data bytes: {body[9:19].hex()}")
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# Walk block 0 manually, comparing each sample
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cur = t1
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samples = [t0, t1]
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block_off = 7
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nn = body[8]
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print(f" NN = {nn}")
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data = body[9 : 9 + nn // 2]
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for byi, byte in enumerate(data):
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for nib_idx, nib in enumerate(((byte >> 4) & 0xF, byte & 0xF)):
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cur += s4(nib)
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samples.append(cur)
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idx = len(samples) - 1
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if 0 <= idx < len(sc_tran):
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sc_v = sc_tran[idx]
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match = "✓" if sc_v == cur else "✗"
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if idx < 12 or 240 <= idx <= 260:
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print(f" idx {idx:3d}: nibble byte={byte:02x} nib={nib:x} delta={s4(nib):+d} cur={cur:+d} sc={sc_v:+d} {match}")
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print(f"end of block 0: cur={cur}, len(samples)={len(samples)}, decoder expected 250 here")
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# Block 1: 20 28 starts at offset 9 + 124 = 133 from block_off=7
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block1_off = 9 + nn // 2
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print(f"block 1: tag {body[block1_off]:02x} {body[block1_off+1]:02x} (expecting 20 28)")
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nn1 = body[block1_off + 1]
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print(f" block 1 NN = {nn1}")
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data1 = body[block1_off + 2 : block1_off + 2 + nn1]
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for byi, byte in enumerate(data1):
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cur += i8(byte)
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samples.append(cur)
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idx = len(samples) - 1
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if idx < len(sc_tran):
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sc_v = sc_tran[idx]
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match = "✓" if sc_v == cur else "✗"
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if 248 <= idx <= 295:
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print(f" idx {idx:3d}: int8 byte={byte:02x} delta={i8(byte):+d} cur={cur:+d} sc={sc_v:+d} {match}")
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if __name__ == "__main__":
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main()
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