feat: speed limit sign UI and speed processing pipeline

New speed_logic.py module converts raw CAN speed limit and GPS speed
into display-ready params. Called from controlsd (live) and
bench_onroad (bench) at ~2Hz. UI reads params to render:
- Current speed (top center, hidden when 0 or no GPS)
- MUTCD speed limit sign (lower-left, normal + nightrider styles)
- Unit-aware display (mph/kph based on CAN DISTANCE_UNIT)

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

selfdrive/clearpilot/bench_onroad.py

@@ -21,8 +21,8 @@ import time
 import cereal.messaging as messaging
 from cereal import log, car
 from openpilot.common.params import Params
-
-MS_PER_MPH = 0.44704
+from openpilot.common.conversions import Conversions as CV
+from openpilot.selfdrive.clearpilot.speed_logic import SpeedState
 
 
 def main():
@@ -36,6 +36,9 @@ def main():
   params_mem.put("BenchGear", "P")
   params_mem.put("BenchEngaged", "0")
 
+  # ClearPilot speed processing
+  speed_state = SpeedState()
+
   # thermald handles deviceState (reads our fake pandaStates for ignition)
   pm = messaging.PubMaster([
     "pandaStates", "carState", "controlsState",
@@ -63,9 +66,15 @@ def main():
       gear_str = (params_mem.get("BenchGear", encoding="utf-8") or "P").strip().upper()
       engaged = (params_mem.get("BenchEngaged", encoding="utf-8") or "0").strip() == "1"
 
-      speed_ms = speed_mph * MS_PER_MPH
+      speed_ms = speed_mph * CV.MPH_TO_MS
+      speed_limit_ms = speed_limit_mph * CV.MPH_TO_MS
       gear = gear_map.get(gear_str, car.CarState.GearShifter.park)
 
+      # ClearPilot speed processing (~2 Hz at 10 Hz loop)
+      if frame % 5 == 0:
+        has_speed = speed_mph > 0
+        speed_state.update(speed_ms, has_speed, speed_limit_ms, is_metric=False)
+
       # pandaStates — 10 Hz (thermald reads ignition from this)
       if frame % 1 == 0:
         dat = messaging.new_message("pandaStates", 1)
@@ -82,7 +91,7 @@ def main():
       cs.standstill = speed_ms < 0.1
       cs.cruiseState.available = True
       cs.cruiseState.enabled = engaged
-      cs.cruiseState.speed = cruise_mph * MS_PER_MPH if cruise_mph > 0 else 0
+      cs.cruiseState.speed = cruise_mph * CV.MPH_TO_MS if cruise_mph > 0 else 0
       pm.send("carState", dat)
 
       # controlsState — 10 Hz

selfdrive/clearpilot/speed_logic.py

@@ -0,0 +1,52 @@
+"""
+ClearPilot speed processing module.
+
+Shared logic for converting raw speed and speed limit data into display-ready
+values. Called from controlsd (live mode) and bench_onroad (bench mode).
+
+Reads raw inputs, converts to display units (mph or kph based on car's CAN
+unit setting), detects speed limit changes, and writes results to params_memory
+for the onroad UI to read.
+"""
+import math
+from openpilot.common.params import Params
+from openpilot.common.conversions import Conversions as CV
+
+
+class SpeedState:
+  def __init__(self):
+    self.params_memory = Params("/dev/shm/params")
+    self.prev_speed_limit = 0
+
+  def update(self, speed_ms: float, has_speed: bool, speed_limit_ms: float, is_metric: bool):
+    """
+    Convert raw m/s values to display-ready strings and write to params_memory.
+
+    Args:
+      speed_ms: current vehicle speed in m/s (from GPS or bench)
+      has_speed: whether we have a valid speed source
+      speed_limit_ms: current speed limit in m/s (from CAN or bench)
+      is_metric: True if car's CAN reports metric units (e.g. Canada)
+    """
+    if is_metric:
+      speed_display = speed_ms * CV.MS_TO_KPH
+      speed_limit_display = speed_limit_ms * CV.MS_TO_KPH
+      unit = "km/h"
+    else:
+      speed_display = speed_ms * CV.MS_TO_MPH
+      speed_limit_display = speed_limit_ms * CV.MS_TO_MPH
+      unit = "mph"
+
+    speed_int = int(math.floor(speed_display))
+    speed_limit_int = int(math.floor(speed_limit_display))
+
+    # Detect speed limit changes (groundwork for future chime)
+    if speed_limit_int != self.prev_speed_limit:
+      self.prev_speed_limit = speed_limit_int
+
+    # Write display-ready values to params_memory
+    self.params_memory.put("ClearpilotHasSpeed", "1" if has_speed and speed_int > 0 else "0")
+    self.params_memory.put("ClearpilotSpeedDisplay", str(speed_int) if has_speed and speed_int > 0 else "")
+    self.params_memory.put("ClearpilotSpeedLimitDisplay", str(speed_limit_int) if speed_limit_int > 0 else "0")
+    self.params_memory.put("ClearpilotSpeedUnit", unit)
+    self.params_memory.put("ClearpilotIsMetric", "1" if is_metric else "0")