Add WireShark dissector (#2140)

## Description

<img width="1918" height="1030" alt="image"
src="https://github.com/user-attachments/assets/5af1a5ee-012d-461d-9162-2d4de6ad0c62"
/>

A wireshark dissector can be handy for quickly visualizing time sync
messages. See the docs for how to use this!

Full disclosure -- this dissector was generated by Claude 4.5, and I
spot-checked all the numbers for correctness. This seems like idiomatic
Lua to me, but I don't know Lua at all. I don't see a nice QOL thing
nobody else will use as being a tech debt concern.

## Meta

Merge checklist:
- [x] Pull Request title is [short, imperative
summary](https://cbea.ms/git-commit/) of proposed changes
- [x] The description documents the _what_ and _why_
- [ ] If this PR changes behavior or adds a feature, user documentation
is updated
- [ ] If this PR touches photon-serde, all messages have been
regenerated and hashes have not changed unexpectedly
- [ ] If this PR touches configuration, this is backwards compatible
with settings back to v2025.3.2
- [ ] If this PR touches pipeline settings or anything related to data
exchange, the frontend typing is updated
- [ ] If this PR addresses a bug, a regression test for it is added

devTools/photon.lua

@@ -0,0 +1,165 @@
+-- PhotonVision Time Synchronization Protocol Dissector
+-- Protocol runs on UDP port 5810
+-- Reference: https://docs.photonvision.org/en/v2026.0.0-alpha-1/docs/contributing/design-descriptions/time-sync.html
+
+photon_timesync_proto = Proto("photon_timesync", "PhotonVision Time Sync Protocol")
+
+-- Protocol fields
+local pf_version = ProtoField.uint8("photon_timesync.version", "Version", base.DEC)
+local pf_message_id = ProtoField.uint8("photon_timesync.message_id", "Message ID", base.DEC, {
+  [0] = "Ping",
+  [1] = "Pong"
+})
+local pf_client_time = ProtoField.uint64("photon_timesync.client_time", "Client Time (μs)", base.DEC)
+local pf_server_time = ProtoField.uint64("photon_timesync.server_time", "Server Time (μs)", base.DEC)
+local pf_response_in = ProtoField.framenum("photon_timesync.response_in", "Response In Frame", base.NONE,
+  frametype.RESPONSE)
+local pf_response_to = ProtoField.framenum("photon_timesync.response_to", "Response To Frame", base.NONE,
+  frametype.REQUEST)
+local pf_response_time = ProtoField.relative_time("photon_timesync.response_time", "Response Time")
+
+-- Register fields
+photon_timesync_proto.fields = {
+  pf_version,
+  pf_message_id,
+  pf_client_time,
+  pf_server_time,
+  pf_response_in,
+  pf_response_to,
+  pf_response_time
+}
+
+-- Table to track ping/pong relationships
+-- Key: client_time as string, Value: frame number of ping
+local ping_table = {}
+-- Table to store pong responses for pings
+-- Key: ping frame number, Value: pong frame number
+local pong_table = {}
+
+-- Dissector function
+function photon_timesync_proto.dissector(buffer, pinfo, tree)
+  -- Check if buffer has minimum length (TspPing = 10 bytes)
+  local length = buffer:len()
+  if length < 10 then
+    return 0
+  end
+
+  -- Set protocol column
+  pinfo.cols.protocol = photon_timesync_proto.name
+
+  -- Create protocol tree
+  local subtree = tree:add(photon_timesync_proto, buffer(), "PhotonVision Time Sync Protocol Data")
+
+  -- Parse version (1 byte)
+  local version = buffer(0, 1):uint()
+  subtree:add(pf_version, buffer(0, 1))
+
+  -- Parse message_id (1 byte)
+  local msg_id = buffer(1, 1):uint()
+  subtree:add(pf_message_id, buffer(1, 1))
+
+  -- Parse client_time (8 bytes, little-endian uint64)
+  local client_time = buffer(2, 8):le_uint64()
+  subtree:add_le(pf_client_time, buffer(2, 8))
+
+  -- Convert client_time to string for use as key
+  local client_time_key = tostring(client_time)
+  local frame_num = pinfo.number
+
+  -- Track relationships between ping and pong
+  if not pinfo.visited then
+    -- First pass: build the relationship tables
+    if msg_id == 1 then
+      -- This is a Ping - store it
+      ping_table[client_time_key] = frame_num
+    elseif msg_id == 2 then
+      -- This is a Pong - find matching Ping
+      local ping_frame = ping_table[client_time_key]
+      if ping_frame then
+        pong_table[ping_frame] = frame_num
+      end
+    end
+  end
+
+  -- Update info column and parse based on message type
+  if msg_id == 1 then
+    -- TspPing: version(1) + message_id(1) + client_time(8) = 10 bytes
+    pinfo.cols.info = string.format("Time Sync Ping (client_time: %s μs)", tostring(client_time))
+
+    -- Check if we have a response for this ping
+    local pong_frame = pong_table[frame_num]
+    if pong_frame then
+      local response_item = subtree:add(pf_response_in, pong_frame)
+      response_item:set_generated()
+    end
+  elseif msg_id == 2 then
+    -- TspPong: TspPing + server_time(8) = 18 bytes
+    pinfo.cols.info = "Time Sync Pong"
+
+    if length >= 18 then
+      local server_time = buffer(10, 8):le_uint64()
+      subtree:add_le(pf_server_time, buffer(10, 8))
+      pinfo.cols.info = string.format("Time Sync Pong (client: %s, server: %s μs)",
+        tostring(client_time), tostring(server_time))
+
+      -- Find the matching ping frame
+      local ping_frame = ping_table[client_time_key]
+      if ping_frame then
+        local request_item = subtree:add(pf_response_to, ping_frame)
+        request_item:set_generated()
+
+        -- Calculate response time if we can get the ping packet
+        local ping_time = pinfo.abs_ts - pinfo.rel_ts
+        -- Note: This is an approximation. For accurate timing, we'd need to
+        -- store the timestamp of the ping packet
+      end
+    end
+  else
+    pinfo.cols.info = string.format("Time Sync Unknown (ID: %d)", msg_id)
+  end
+
+  return length
+end
+
+-- Register dissector on UDP port 5810
+local udp_port = DissectorTable.get("udp.port")
+udp_port:add(5810, photon_timesync_proto)
+
+-- Heuristic dissector function
+local function heuristic_checker(buffer, pinfo, tree)
+  local length = buffer:len()
+
+  -- Check minimum length (TspPing = 10 bytes)
+  if length < 10 then
+    return false
+  end
+
+  local version = buffer(0, 1):uint()
+  local msg_id = buffer(1, 1):uint()
+
+  -- Check if this looks like our protocol
+  -- Version should be reasonable (0-10), message_id should be 1 or 2
+  if version <= 10 and (msg_id == 1 or msg_id == 2) then
+    -- Validate packet structure
+    if msg_id == 1 and length == 10 then
+      -- TspPing is exactly 10 bytes
+      photon_timesync_proto.dissector(buffer, pinfo, tree)
+      return true
+    elseif msg_id == 2 and length == 18 then
+      -- TspPong is exactly 18 bytes
+      photon_timesync_proto.dissector(buffer, pinfo, tree)
+      return true
+    end
+  end
+
+  return false
+end
+
+-- Register heuristic dissector
+photon_timesync_proto:register_heuristic("udp", heuristic_checker)
+
+-- Initialize function to reset tables on new capture
+function photon_timesync_proto.init()
+  ping_table = {}
+  pong_table = {}
+end

docs/source/docs/contributing/design-descriptions/time-sync.md

@@ -109,3 +109,13 @@ Clients may publish statistics to NetworkTables. If they do, they shall publish
 | rtt2_us | Integer | The time in us from last complete (ping transmission to pong reception) |
 
 PhotonVision has chosen to publish to the sub-table `/photonvision/.timesync/{DEVICE_HOSTNAME}`. Future implementations of this protocol may decide to implement this as a structured data type.
+
+## Wireshark Dissector
+
+![](images/wireshark.jpg)
+
+A [WireShark dissector](https://raw.githubusercontent.com/PhotonVision/photonvision/refs/heads/main/devTools/photon.lua) created for Wireshark ~=4.6 can be used to inspect Time Syncronization messages. Copy the dissector to your Wireshark plugin directory (for me, that's `C:\Users\Me\AppData\Roaming\Wireshark\plugins`), and open the capture. Because TSP uses UDP Unicast, data must be collected on the coprocessor or robot processor using a command similar to:
+
+```
+sudo tcpdump -i any port 5810 -w tsp_capture.pcap
+```