fix(protocol): correct A5 frame classification and chunk counter formula

minimateplus/blastware_file.py

@@ -527,7 +527,7 @@ def classify_frame(frame: S3Frame) -> str:
 
     Returns one of:
         "terminator"    — page_key == 0x0000
-        "probe_or_strt" — data contains b"STRT" (the initial probe response)
+        "probe_or_strt" — data contains b"STRT\xff\xfe" (the initial probe response)
         "metadata"      — data contains ASCII compliance-config markers
         "waveform"      — predominantly binary (< 20 % printable ASCII)
         "unknown"       — none of the above criteria matched
@@ -539,7 +539,7 @@ def classify_frame(frame: S3Frame) -> str:
     if frame.page_key == 0x0000:
         return "terminator"
     data = bytes(frame.data)
-    if b"STRT" in data:
+    if b"STRT\xff\xfe" in data:
         return "probe_or_strt"
     if any(m in data for m in _METADATA_FRAME_MARKERS):
         return "metadata"
@@ -677,6 +677,7 @@ def write_blastware_file(
         term_frame  = None
 
     all_bytes = bytearray()
+    seen_metadata = False
 
     for fi, frame in enumerate(body_frames):
         ftype = classify_frame(frame)
@@ -686,11 +687,20 @@ def write_blastware_file(
             # Probe frame: always process regardless of classification.
             # It holds the STRT record; probe_skip positions us past it.
             skip = probe_skip
-        elif ftype == "waveform":
+        elif seen_metadata:
+            # Drop all frames that come after the compliance/metadata block.
+            # (e.g. extra waveform chunks fetched after stop_after_metadata)
+            log.debug(
+                "write_blastware_file: frame %d after metadata — skipping", fi
+            )
+            continue
+        elif ftype in ("waveform", "metadata"):
             skip = 13 if fi == 1 else 12
+            if ftype == "metadata":
+                seen_metadata = True
         else:
-            # Skip metadata, probe_or_strt, and unknown frames.
-            if b"STRT" in bytes(frame.data):
+            # Skip probe_or_strt and unknown frames.
+            if b"STRT\xff\xfe" in bytes(frame.data):
                 log.warning(
                     "write_blastware_file: frame %d (%s) contains STRT — skipping",
                     fi, ftype,

minimateplus/protocol.py

@@ -126,10 +126,12 @@ DATA_LENGTHS: dict[int, int] = {
 _BULK_CHUNK_OFFSET = 0x1004   # offset field for probe + all regular chunk requests ✅
 _BULK_TERM_OFFSET  = 0x005A   # offset field for termination request ✅
 _BULK_COUNTER_STEP = 0x0400   # chunk counter increment per chunk ✅
-# Chunk counter formula: chunk_num * 0x0400 for ALL chunks including chunk 1.
-# Earlier captures showed 0x1004 for chunk 1 — that was a Blastware artifact, not a
-# protocol requirement.  Confirmed 2026-04-06: 0x0400 for chunk 1 works; 0x1004
-# causes a 120-second device timeout.  Formula n * 0x0400 is used for all chunks.
+# Chunk counter formula: key4[2:4] + (chunk_num - 1) * 0x0400
+# where key4[2:4] is the event's circular-buffer base offset ((key4[2]<<8)|key4[3]).
+# Earlier captures showed 0x1004 for chunk 1 of key 01110000 — that was a Blastware
+# artifact.  For keys where key4[2:4] != 0x0000 (e.g. key 01111884) the old
+# "n * 0x0400" formula sends counters from the wrong buffer region and the device
+# returns data from a different event.  Confirmed correct 2026-04-24.
 
 # Default timeout values (seconds).
 # MiniMate Plus is a slow device — keep these generous.