ROS time (sim_time) support

Introduction

CARET uses system time to analyze trace data by default. It may be inconvenient, especially when treating trace data recorded with rosbag. These are examples:

• The flow of time in analysis results (e.g., time series graph) is different from that of ROS when playing rosbag with [-r RATE] option. For instance, 10 Hz becomes 2 Hz when rosbag was played with [-r 0.2] but analysis uses system time
• Time becomes different at every recording even if you use the same rosbag file, which makes comparing experimental results difficult

This page explains how to use sim_time.

Recording /clock topic

/clock topic needs to be recorded in trace data. /clock topis is recorded as ros2_caret:sim_time event in trace data.

Open a new terminal and run the following commands before recording and running a target application.

Info

Remember to set use_sim_time=true for each node when launching a target application
Remember to add --clock option when playing rosbag

source /opt/ros/humble/setup.bash
source ~/ros2_caret_ws/install/local_setup.bash

ros2 run caret_trace clock_recorder

You can check whether /clock is successfully recorded by the following command.

babeltrace <path-to-trace-data> | cut -d' ' -f 4 | sort -u | grep sim_time

---Expected output text as below---

ros2_caret:sim_time:

Visualization using sim_time

By setting use_sim_time=True or xaxis_type='sim_time', sim_time is used instead of system time for the following APIs.

def callback_sched(
    target: CallbackGroupTypes,
    lstrip_s: float = 0,
    rstrip_s: float = 0,
    coloring_rule: str = 'callback',
    use_sim_time: bool = False,
    export_path: Optional[str] = None
) -> Figure:

def message_flow(
    path: Path,
    export_path: Optional[str] = None,
    granularity: Optional[str] = None,
    treat_drop_as_delay=False,
    lstrip_s: float = 0,
    rstrip_s: float = 0,
    use_sim_time: bool = False
) -> Figure:

def show(
    self,
    xaxis_type: str = 'system_time',
    ywheel_zoom: bool = True,
    full_legends: bool = False,
    export_path: Optional[str] = None
) -> Figure:

In case /clock topic is not recorded in trace data, the following error will occur.

InvalidArgumentError: Failed to load sim_time. Please measure again with clock_recorder running.

Sample to use sim_time

Explanation below assumes CARET is installed to ~/ros2_caret_ws and the sample application used in the tutorial section is located in ~/ros2_ws.

Record rosbag

The following steps can be performed either with or without CARET. If you have built a target application without CARET, you don't need to set environment for CARET and LD_PRELOAD.

1. Open a terminal to run a target application to record rosbag

   source /opt/ros/humble/setup.bash
   source ~/ros2_caret_ws/install/local_setup.bash
   source ~/ros2_ws/install/local_setup.bash
   export LD_PRELOAD=$(readlink -f ~/ros2_caret_ws/install/caret_trace/lib/libcaret.so)
   
   ros2 run caret_demos end_to_end_sample
   

2. Open another terminal to record rosbag

   source /opt/ros/humble/setup.bash
   source ~/ros2_ws/install/local_setup.bash
   
   ros2 bag record /topic1 /drive
   

   Here, /topic1 and /drive are source topics of the sample application.
   You can check if rosbag is successfully recorded.

   ros2 bag info rosbag2_2022_09_30-10_57_06
   
   Files:             rosbag2_2022_09_30-10_57_06_0.db3
   Bag size:          29.3 KiB
   Storage id:        sqlite3
   Duration:          9.601s
   Start:             Sep 30 2022 10:57:08.952 (1664503028.952)
   End:               Sep 30 2022 10:57:18.554 (1664503038.554)
   Messages:          194
   Topic information: Topic: /drive | Type: sensor_msgs/msg/Image | Count: 97 | Serialization Format: cdr
                   Topic: /topic1 | Type: sensor_msgs/msg/Image | Count: 97 | Serialization Format: cdr
   

Record trace data

1. Open another terminal and run the following commands

   source /opt/ros/humble/setup.bash
   source ~/ros2_caret_ws/install/local_setup.bash
   
   ros2 run caret_trace clock_recorder
   

2. Open another terminal to run a target application to record trace data with CARET

   In the launch file, use_sim_time is set to true and source nodes are disabled.

    source /opt/ros/humble/setup.bash
    source ~/ros2_caret_ws/install/local_setup.bash
    source ~/ros2_ws/install/local_setup.bash
    export LD_PRELOAD=$(readlink -f ~/ros2_caret_ws/install/caret_trace/lib/libcaret.so)
   
    ros2 launch caret_demos end_to_end_sample_with_lttng_session_use_sim.launch.py use_sim_time:=true use_rosbag:=true
   

3. Open another terminal to play the rosbag

    source /opt/ros/humble/setup.bash
    source ~/ros2_ws/install/local_setup.bash
   
    ros2 bag play rosbag2_2022_09_30-10_57_06 --clock -r 0.2
   

4. Stop the application and the rosbag

5. Check if /clock topic is recorded in trace data as sim_time

   babeltrace ~/ros2_ws/evaluate/e2e_sample | cut -d' ' -f 4 | sort -u | grep sim_time
   ros2_caret:sim_time:
   

Visualize results using sim_time

1. Launch Jupyter Notebook in ~/ros2_ws/evaluate and run the following scripts
   • Reference: the tutorial

from bokeh.plotting import output_notebook
output_notebook()
from caret_analyze import Architecture, Application, Lttng
from caret_analyze.plot import Plot, message_flow

# Read trace data
arch = Architecture('lttng', './e2e_sample')
lttng = Lttng('./e2e_sample')

# Search and add path
paths = arch.search_paths(
    '/filter_node',
    '/message_driven_node')
arch.add_path('target_path', paths[0])
app = Application(arch, lttng)

# Draw message_flow
path = app.get_path('target_path')
message_flow(path, use_sim_time=True)

# Draw node info
node = app.get_node('/filter_node')
plot = Plot.create_callback_period_plot(node.callbacks)
plot.show('sim_time')