fix 0x3400 parsing to use offset-based string references

2026-01-23 21:49:12 -08:00
parent 71aa3bfc3e
commit 694a51eade
3 changed files with 147 additions and 52 deletions
--- a/notes/dantepacket.md
+++ b/notes/dantepacket.md
@@ -0,0 +1,134 @@
+# Dante Control Protocol Notes
+
+All Dante control packets are UDP on port 4440.
+
+## Packet Header (10 bytes)
+
+```
+0x00: u8   magic        # 0x27=standard, 0x28=extended
+0x01: u8   seq_lo
+0x02: u16  length       # total packet length
+0x04: u16  seq_id
+0x06: u16  command
+0x08: u16  status
+0x0a: ...  args/data
+```
+
+All multi-byte fields are big-endian.
+
+## Commands
+
+### 0x1000 - Channel Count Query
+
+Response:
+```
+0x0c: u16  tx_count
+0x0e: u16  rx_count
+```
+
+### 0x3000 - Subscription Query (Standard)
+
+Works for multicast; may return empty for unicast.
+
+Request args (6 bytes):
+```
+0x00: u16  0x0001
+0x02: u16  page_num
+0x04: u16  0x0000
+```
+
+Response record types (at 0x0e):
+- `0x0006` = unicast
+- `0x000e` = multicast
+
+### 0x3400 - Subscription Query (Extended)
+
+Uses magic=0x28. Works for unicast flows.
+
+Request args (24 bytes):
+```
+0x07: u8   0x01
+0x08: u16  page_type    # 0x0001=first, 0x0003=subsequent
+0x0a: u16  start_ch     # 1, 17, 33, 49, ...
+```
+
+## 0x3400 Response
+
+```
+0x00: [10] header
+0x0a: [8]  extended_header
+0x12: [32] offset_table     # 16 × u16 record offsets
+0x32: ...  records + strings
+```
+
+Status (at 0x08):
+- `0x8112` = has subscription data
+- `0x0001` = empty page
+
+### Offset Table
+
+16 entries at 0x12-0x31, each a u16 absolute offset to a record.
+Zero offset = no more records.
+
+### Subscription Record
+
+Each record is 56+ bytes. The offset table points to record start.
+
+```
+record+0x00: [40] record_header
+record+0x28: u16  0x0608          # marker
+record+0x2a: u16  0x0000
+record+0x2c: u16  tx_ch_offset    # absolute offset to TX channel name string
+record+0x2e: u16  tx_dev_offset   # absolute offset to TX device name string
+record+0x30: [4]  flags
+record+0x34: u32  0x02020000      # string marker
+record+0x38: ...  inline_strings  # (unreliable, use offsets above)
+```
+
+**Subscription status:**
+- Both offsets non-zero = subscribed
+- Both offsets zero = unsubscribed
+
+### String Table
+
+Null-terminated strings referenced by absolute offset from packet start.
+Multiple records share strings (e.g., same device name).
+
+## Example: Page 2 Response (channels 17-32)
+
+```
+Offset table: 0050 0090 00d0 0110 0158 0194 01d8 021c 0258 ...
+
+Record at 0x0050 (RX ch 17):
+  0x0050+0x2c: 0032 0035
+  String at 0x32: "01"       -> TX channel
+  String at 0x35: "MICS-E"   -> TX device
+  Result: MICS-E[01] -> ch17
+
+Record at 0x0158 (RX ch 21):
+  0x0158+0x2c: 0032 0148
+  String at 0x32: "01"
+  String at 0x148: "TX-QLAB-1"
+  Result: TX-QLAB-1[01] -> ch21
+
+Record at 0x01d8 (RX ch 23):
+  0x01d8+0x2c: 01cc 01d1
+  String at 0x1cc: "Left"
+  String at 0x1d1: "BT"
+  Result: BT[Left] -> ch23
+
+Record at 0x0258 (RX ch 25):
+  0x0258+0x2c: 0000 0000
+  Result: UNSUBSCRIBED
+```
+
+## Parsing Algorithm
+
+1. Check magic=0x28, command=0x3400, status=0x8112
+2. Read 16 offsets from 0x12-0x31
+3. For each non-zero offset:
+   - Read u16 at offset+0x2c (tx_ch_offset)
+   - Read u16 at offset+0x2e (tx_dev_offset)
+   - If both zero: skip (unsubscribed)
+   - Else: read null-terminated strings at those offsets
+   - RX channel = page_start + record_index