diff --git a/docker-compose.yml b/docker-compose.yml
index 430ea1a..96071e4 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -7,6 +7,7 @@ services:
     environment:
       - RUST_LOG=info
       - MOCK_TEENSY=1
+      - HACI_SERIAL_PORT=/dev/ttyACM0
     ports:
       - "8080:8080"
     volumes:
diff --git a/scripts/entrypoint.sh b/scripts/entrypoint.sh
index dcde2a1..acdd5e7 100644
--- a/scripts/entrypoint.sh
+++ b/scripts/entrypoint.sh
@@ -20,6 +20,9 @@ if [ "${MOCK_TEENSY:-0}" = "1" ]; then
   done
   if [ ! -e /dev/ttyACM0 ]; then
     echo "[entrypoint] WARNING: Failed to create /dev/ttyACM0 (mock Teensy)" >&2
+  else
+    export HACI_SERIAL_PORT=/dev/ttyACM0
+    echo "[entrypoint] Using mock serial at $HACI_SERIAL_PORT" >&2
   fi
 fi
 
diff --git a/scripts/ltc_gen.sh b/scripts/ltc_gen.sh
index 9d1c0b8..0f4ca66 100644
--- a/scripts/ltc_gen.sh
+++ b/scripts/ltc_gen.sh
@@ -21,7 +21,7 @@ s=0
 f=0
 
 while true; do
-  printf "LOCK %02d:%02d:%02d;%02d %s\r\n" "$h" "$m" "$s" "$f" "$RATE_STR"
+  printf "[LOCK] %02d:%02d:%02d;%02d | %sfps\r\n" "$h" "$m" "$s" "$f" "$RATE_STR"
 
   # increment frame
   f=$((f+1))