telemetry: diff-based CSV logger with ZMQ IPC

- telemetry.py: client library, tlog(group, data) sends JSON over ZMQ PUSH
- telemetryd.py: collector process, diffs against previous state per group,
  writes only changed values to /data/log2/{session}/telemetry.csv
- Registered as always-run managed process in process_config.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

selfdrive/clearpilot/telemetry.py

@@ -0,0 +1,34 @@
+"""
+ClearPilot telemetry client library.
+
+Usage from any process:
+  from openpilot.selfdrive.clearpilot.telemetry import tlog
+  tlog("canbus", {"speed": 45.2, "speed_limit": 60})
+
+Sends JSON packets over ZMQ PUSH to telemetryd, which diffs and writes CSV.
+"""
+import json
+import time
+import zmq
+
+TELEMETRY_SOCK = "ipc:///tmp/clearpilot_telemetry"
+
+_ctx = None
+_sock = None
+
+
+def tlog(group: str, data: dict):
+  """Log a telemetry packet. Only changed values will be written to CSV by telemetryd."""
+  global _ctx, _sock
+  if _sock is None:
+    _ctx = zmq.Context.instance()
+    _sock = _ctx.socket(zmq.PUSH)
+    _sock.setsockopt(zmq.LINGER, 0)
+    _sock.setsockopt(zmq.SNDHWM, 100)
+    _sock.connect(TELEMETRY_SOCK)
+
+  msg = json.dumps({"ts": time.time(), "group": group, "data": data})
+  try:
+    _sock.send_string(msg, zmq.NOBLOCK)
+  except zmq.Again:
+    pass  # drop if collector isn't running or queue full

selfdrive/clearpilot/telemetryd.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+"""
+ClearPilot telemetry collector.
+
+Receives telemetry packets from any process via ZMQ, diffs against previous
+state per group, and writes only changed values to CSV.
+
+CSV format: timestamp,group,key,value
+"""
+import csv
+import json
+import os
+import zmq
+
+from openpilot.selfdrive.clearpilot.telemetry import TELEMETRY_SOCK
+from openpilot.selfdrive.manager.process import _log_dir
+
+
+def main():
+  ctx = zmq.Context.instance()
+  sock = ctx.socket(zmq.PULL)
+  sock.setsockopt(zmq.RCVHWM, 1000)
+  sock.bind(TELEMETRY_SOCK)
+
+  csv_path = os.path.join(_log_dir, "telemetry.csv")
+  state: dict[str, dict] = {}  # group -> {key: last_value}
+
+  with open(csv_path, "w", newline="") as f:
+    writer = csv.writer(f)
+    writer.writerow(["timestamp", "group", "key", "value"])
+    f.flush()
+
+    while True:
+      try:
+        raw = sock.recv_string()
+      except zmq.ZMQError:
+        continue
+
+      try:
+        pkt = json.loads(raw)
+      except json.JSONDecodeError:
+        continue
+
+      ts = pkt.get("ts", 0)
+      group = pkt.get("group", "")
+      data = pkt.get("data", {})
+
+      if group not in state:
+        state[group] = {}
+
+      prev = state[group]
+      changed = False
+
+      for key, value in data.items():
+        # Convert to string for comparison so floats/ints/bools all diff correctly
+        str_val = str(value)
+        if key not in prev or prev[key] != str_val:
+          writer.writerow([f"{ts:.6f}", group, key, str_val])
+          prev[key] = str_val
+          changed = True
+
+      if changed:
+        f.flush()
+
+
+if __name__ == "__main__":
+  main()