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fix(lf): read() acquired with the field OFF (SNIFF) — no tag was ever powered

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lf.read() sent CMD_LF_SNIFF_RAW_ADC (passive sniff, reader field OFF), so it captured
only a dead field — a real hardware dump came back flat at 0x7e-0x80 (±1 count of ADC
noise) with no tag modulation, which is why LF identify found nothing. Reader-mode reads
must use CMD_LF_ACQ_RAW_ADC (SampleLF -> field ON) to power the tag and capture its load
modulation.

- read() -> CMD_LF_ACQ_RAW_ADC (field on); sniff() -> CMD_LF_SNIFF_RAW_ADC (field off),
  no longer delegating to read(). Shared _acquire() packs the real lf_sample_payload_t
  (PACKED bitfield samples:30/realtime:1/verbose:1 + cotag byte = 5 bytes) instead of a
  bare uint32.

Tests: read() uses ACQ with a 5-byte payload and correct samples field; sniff() uses SNIFF.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
michael
2026-07-14 16:17:11 -07:00
parent 2f221644f9
commit b536294a7a
2 changed files with 42 additions and 9 deletions
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27
pm3py/core/lf.py
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@@ -111,23 +111,32 @@ class LFCommands:
return result
async def read(self, samples: int = 12288, verbose: bool = False,
on_progress: ProgressCallback = None) -> dict:
"""Read LF ADC samples into device buffer."""
val = (samples & 0x3FFFFFFF)
async def _acquire(self, cmd: int, samples: int, verbose: bool = False) -> dict:
"""Capture LF ADC samples into BigBuf. Shared by read (reader field ON) and sniff
(field OFF). Payload is lf_sample_payload_t — a PACKED bitfield: samples:30, realtime:1,
verbose:1, cotag:1 (5 bytes)."""
word = (samples & 0x3FFFFFFF)
if verbose:
val |= (1 << 31)
payload = struct.pack("<I", val)
resp = await self._t.send_ng(Cmd.LF_SNIFF_RAW_ADC, payload, timeout=10.0)
word |= (1 << 31) # bit 31 = verbose; bit 30 = realtime (0)
payload = struct.pack("<IB", word, 0) # trailing byte carries cotag (0)
resp = await self._t.send_ng(cmd, payload, timeout=10.0)
return {
"status": resp.status,
"samples": struct.unpack_from("<I", resp.data, 0)[0] if len(resp.data) >= 4 else 0,
}
async def read(self, samples: int = 12288, verbose: bool = False,
on_progress: ProgressCallback = None) -> dict:
"""Reader-mode LF acquisition: turn the reader field ON and sample the tag's load
modulation (this is ``lf read`` — CMD_LF_ACQ_RAW_ADC). Use this before download_samples
to read an EM4100/T5577/HID. (SNIFF, field-off, captures nothing from a tag.)"""
return await self._acquire(Cmd.LF_ACQ_RAW_ADC, samples, verbose)
async def sniff(self, samples: int = 12288,
on_progress: ProgressCallback = None) -> dict:
"""Sniff LF signal."""
return await self.read(samples=samples, on_progress=on_progress)
"""Sniff LF: reader field OFF, capture an external reader<->tag exchange
(CMD_LF_SNIFF_RAW_ADC)."""
return await self._acquire(Cmd.LF_SNIFF_RAW_ADC, samples)
async def sim(self, gap: int = 0, data: bytes = b"",
on_progress: ProgressCallback = None) -> dict: