From 242666f3583134b9920790970f7ca1e3e90aec86 Mon Sep 17 00:00:00 2001
From: Brian Harrison <brianharrison02@gmail.com>
Date: Fri, 24 Apr 2026 12:52:02 -0400
Subject: [PATCH] fix(protocol): correct chunk counter formula for accurate
 data streaming

---
 minimateplus/protocol.py | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/minimateplus/protocol.py b/minimateplus/protocol.py
index 9f48bc5..5a2537f 100644
--- a/minimateplus/protocol.py
+++ b/minimateplus/protocol.py
@@ -583,8 +583,17 @@ class MiniMateProtocol:
         frames_data: list[S3Frame] = []
         counter = 0
 
+        # BW counter formula (confirmed from 4-3-26 capture for key 0111245a):
+        #   counter for chunk n = key4[2:4] + (n - 1) * 0x0400
+        # key4[2:4] is the event's circular-buffer base offset — without it, chunk
+        # requests address the wrong region of the device buffer and the device
+        # streams data from the wrong event (no "Project:" in any response).
+        # PREVIOUSLY WRONG NOTE: "device does not validate counter; chunk_num*0x0400
+        # is correct" — that was only true for key 01110000 where key4[2:4]==0x0000.
+        _key4_offset = (key4[2] << 8) | key4[3]
+
         # ── Step 1: probe ────────────────────────────────────────────────────
-        log.debug("5A probe  key=%s", key4.hex())
+        log.debug("5A probe  key=%s  key4_offset=0x%04X", key4.hex(), _key4_offset)
         params = bulk_waveform_params(key4, 0, is_probe=True)
         self._send(build_5a_frame(_BULK_CHUNK_OFFSET, params))
         self._parser.reset()        # reset bytes_fed counter before probe recv
@@ -601,13 +610,15 @@ class MiniMateProtocol:
         log.debug("5A A5[0]  page_key=0x%04X  %d bytes", rsp.page_key, len(rsp.data))
 
         # ── Step 2: chunk loop ───────────────────────────────────────────────
-        # Chunk counters are monotonic: chunk_num * 0x0400 for all chunks.
-        # The 4-2-26 BW TX capture showed 0x1004 for chunk 1, but this is a
-        # Blastware artifact — the device accepts any counter value and streams
-        # data regardless.  Empirically confirmed 2026-04-06: 0x0400 for chunk 1
-        # works; 0x1004 causes the device to ignore the frame (timeout).
+        # Correct counter formula: key4[2:4] + (chunk_num - 1) * 0x0400
+        # This matches Blastware exactly (confirmed from 4-3-26 capture).
+        # For events where key4[2:4]==0 (e.g. 01110000), this gives the same
+        # result as the old chunk_num*0x0400 formula shifted by one step, which
+        # the device also accepted — but for events with a non-zero base offset
+        # (e.g. key 01111884 with key4[2:4]=0x1884) the old formula sends
+        # completely wrong counters and the device streams the wrong buffer region.
         for chunk_num in range(1, max_chunks + 1):
-            counter = chunk_num * _BULK_COUNTER_STEP
+            counter = _key4_offset + (chunk_num - 1) * _BULK_COUNTER_STEP
             params  = bulk_waveform_params(key4, counter)
             log.debug("5A chunk %d  counter=0x%04X", chunk_num, counter)
             self._send(build_5a_frame(_BULK_CHUNK_OFFSET, params))
@@ -662,7 +673,7 @@ class MiniMateProtocol:
                           chunk_num, extra_chunks_after_metadata)
                 for _extra_n in range(extra_chunks_after_metadata):
                     chunk_num += 1
-                    counter = chunk_num * _BULK_COUNTER_STEP
+                    counter = _key4_offset + (chunk_num - 1) * _BULK_COUNTER_STEP
                     params = bulk_waveform_params(key4, counter)
                     self._send(build_5a_frame(_BULK_CHUNK_OFFSET, params))
                     try: