CLAUDE.md

@@ -386,7 +386,7 @@ bytes `\x01\x2c` = 300 (5-minute default histogram interval); changes when inter
 
 | Offset | Field | Format | Notes |
 |---|---|---|---|
-| anchor − 7 (write) / anchor − 8 (read) | recording_mode | uint8 | E5 read has extra `0x10` at anchor−7 |
+| anchor − 8 | recording_mode | uint8 | **Same offset for both read and write.** The byte at anchor−7 is a `0x10` DLE marker regenerated by device firmware in every E5 response — do NOT overwrite it. Writing to anchor−7 causes anchor drift (+1 per write cycle). CORRECTION 2026-04-21: previous doc stated anchor−7 for write; empirically wrong. |
 | anchor − 6 | sample_rate | uint16 BE | same in read & write |
 | anchor − 4 | histogram_interval_sec | uint16 BE | seconds; same in read & write ✅ 2026-04-20 |
 | anchor − 2 | `0x00 0x00` | padding | |

minimateplus/client.py

@@ -1770,10 +1770,13 @@ def _encode_compliance_config(
     DLE-jitter shifts):
 
       Anchor: b'\\xbe\\x80\\x00\\x00\\x00\\x00'  (confirmed stable, both BE11529 and BE18189)
-        recording_mode       → uint8 at anchor_pos - 7  (write payload)
+        recording_mode       → uint8 at anchor_pos - 8  (BOTH read and write)
                                Values: 0x00=Single Shot, 0x01=Continuous, 0x03=Histogram, 0x04=Histogram+Continuous
-                               NOTE: In the E5 read response (decode) field is at anchor_pos - 8 due to an
+                               NOTE: The byte at anchor_pos - 7 is always 0x10 (a DLE marker regenerated by
-                               extra 0x10 byte at read anchor_pos - 7.  Write payload has no extra byte.
+                               device firmware in every E5 response).  It must NOT be overwritten during
+                               write — doing so causes anchor drift (+1 per write cycle).
+                               CORRECTION 2026-04-21: previous doc stated anchor-7 for write; empirically
+                               confirmed wrong — writing to anchor-7 shifts the anchor by 1 on every cycle.
         sample_rate          → uint16 BE at anchor_pos - 6
         histogram_interval_sec → uint16 BE at anchor_pos - 4  (seconds; mode-gated to Histogram/Histogram+Continuous)
                                Valid values: 2, 5, 15, 60, 300, 900 (= 2s, 5s, 15s, 1m, 5m, 15m)
@@ -1844,9 +1847,10 @@ def _encode_compliance_config(
     else:
         log.info(
             "_encode_compliance_config: anchor at cfg[%d]  buf_len=%d  "
-            "(expected ~15; fields: recording_mode@%d  sample_rate@%d:%d  "
+            "(recording_mode@%d  DLE_marker@%d  sample_rate@%d:%d  "
             "histogram_interval@%d:%d  record_time@%d:%d)",
             _anc, len(buf),
+            _anc - 8,
             _anc - 7,
             _anc - 6, _anc - 4,
             _anc - 4, _anc - 2,
@@ -1854,12 +1858,18 @@ def _encode_compliance_config(
         )
 
     if recording_mode is not None:
-        if _anc < 7:
+        if _anc < 8:
             log.warning("_encode_compliance_config: anchor not found — cannot write recording_mode")
         else:
-            buf[_anc - 7] = recording_mode & 0xFF
+            # Write to anchor-8, same physical position as the E5 read format.
+            # The byte at anchor-7 is a DLE marker (0x10) that the device firmware
+            # regenerates in every E5 response — it must NOT be overwritten.
+            # Writing to anchor-7 causes the device to add an extra byte on the
+            # next read-back, drifting the anchor by +1 on every write cycle.
+            # (CLAUDE.md "anchor-7 write" was incorrect — confirmed 2026-04-21)
+            buf[_anc - 8] = recording_mode & 0xFF
             log.debug("_encode_compliance_config: recording_mode=0x%02X -> offset %d",
-                      recording_mode, _anc - 7)
+                      recording_mode, _anc - 8)
 
     if sample_rate is not None:
         if _anc < 6: