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