Package Summary

The Epson IMU Driver using UART interface for ROS package

Package Summary

The Epson IMU Driver using UART interface for ROS package

Epson IMU ROS1 Node UART

ess_sensors/g552.jpg ess_sensors/g370.jpg ess_sensors/g365.jpg


  • The Epson IMU ROS software is C++ wrapper around a Linux C driver for communicating on a ROS system

  • This code assumes that the user is familiar with building ROS1 packages using the catkin build process
  • This is *NOT* detailed step by step instructions describing how to build and install this ROS driver
  • Refer to the inside the ROS package for more detailed up-to-date technical info on usage

UART Connection & Configuration

  • When connecting the Epson device to a ROS system using the UART interface:
    • direct connection to UART port must be compatible with CMOS 3.3V I/O
    • connection is also possible through a USB-UART 3.3V converter IC such as on the M-G32EV041 evaluation board

    • GPIO output for asserting RESET# pin on the IMU is optional, but recommended if possible (i.e. embedded platforms)
    • Below is an example IMU UART connection when using a Raspberry Pi:
      • Epson IMU

        Raspberry Pi

        EPSON_SIN Input

        RPI_GPIO_P1_8 (GPIO14/UART_TXD) Output

        EPSON_SOUT Output

        RPI_GPIO_P1_10 (GPIO15/UART_RXD) Input

        EPSON_RESET Input

        RPI_GPIO_P1_15 (GPIO22) Output *Optional

  • When connecting the Epson G552PR1/G552PR7 to a ROS system using a RS422 UART interface:
    • direct connection to RS422 UART port must be compatible with RS422 I/O signal levels
    • Below is an example IMU RS422 connection to a RS422 Host:
      • Epson IMU

        RS422 Host

        EPSON_TD+ Output

        HOST_RD+ Input

        EPSON_TD- Output

        HOST_RD- Input

        EPSON_RD+ Input

        HOST_TD+ Output

        EPSON_RD- Input

        HOST_TD- Output

ROS1 Node

Published Topics

  • For all IMU models (except for G365 when quaternion output function is enabled), the orientation field in sensor_msgs/Imu will not contain valid data and should be ignored

  • imu/data_raw - only header, angular velocity, and linear acceleration are valid. Orientation field should be ignored

    sec: 1602020116
    nanosec: 892343523
  frame_id: imu_link
  x: 0.0
  y: 0.0
  z: 0.0
  w: 0.0
orientation_covariance: [-1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
  x: 0.0008243194897659123
  y: 9.91016931948252e-05
  z: -0.00020670934463851154
angular_velocity_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
  x: -1.4295457601547241
  y: -2.184906244277954
  z: 9.49894905090332
linear_acceleration_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
  • For IMU model G365 when quaternion output function is enabled, the orientation field in sensor_msgs/Imu will contain valid data

  • imu/data - header, orientation (quaternion), angular velocity, and linear acceleration

    sec: 1602020004
    nanosec: 667342534
  frame_id: imu_link
  x: -0.11234959959983826
  y: 0.07211977988481522
  z: 0.007866359315812588
  w: 0.9910168647766113
orientation_covariance: [-1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
  x: -0.0018992983968928456
  y: 0.0007579181110486388
  z: 0.0010170674649998546
angular_velocity_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
  x: -1.4219565391540527
  y: -2.176177740097046
  z: 9.500624656677246
linear_acceleration_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

Launch File

  • The roslaunch/XML in the launch folder of this package is used to pass the init parameters to configure the IMU at runtime using roslaunch

  • Changes to init parameters by editing the launch file does not require rebuilding with catkin
  • The following is a brief description of sample launch files:

Launch File



launch file for G320, G354, G364 orientation field data should be ignored


launch file for G365 orientation field data is valid


launch file for G365 without quaternion enabled orientation field data should be ignored


launch file for G370 orientation field data should be ignored


*legacy* launch file for V340 orientation field data should be ignored

Init Parameters

  • The following is a list of typical init parameter settings in a launch file (refer to the individual launch file for full listing and embedded comments)
  • For more technical descriptions of register settings please refer to the specific IMU datasheet
  • Typically, the user only needs to modify dout_rate & filter_sel as needed based on system requirements

Init Parameter



specifies the IMU output data rate in Hz


specifies the IMU filter setting


specifies the function of the GPIO2 ( GPIO2, External Trigger, External Counter Reset). External Counter Reset can be used with GPIO2 to connect to 3.3V compatible GNSS 1PPS signal for time synchronization purpose


specifies the polarity of the GPIO2 pin when External Trigger or External Counter Reset is selected


specifies to enable or disable counter in IMU output data (must be enabled when time_correction is enabled)


enables time correction function using IMU counter reset function & external 1PPS connection to IMU GPIO2/EXT pin. (Must have ext_sel=1 (external counter reset). Attempts to time align the IMU message to the most resent 1 PPS pulse


specifies to enable or disable Quaternion in IMU output data (only support for G365)


specifies the attitude mode as 0=inclination or 1=euler. Typically, set to euler when used (only support for G365)


specifies the attitude motion profile (supported only for G365PDF1)

Timestamping With EXT Signal

  • The G3xx series Epson IMU has 3.3V I/O EXT (GPIO2) pin which can be connected to a cyclic external sync signal such as a GNSS 1PPS signal
  • When this pin is enabled with external counter reset function (refer to the IMU datasheet for more details) a free running internal 16-bit up-counter value is sent out with every sensor sample
  • Every active edge that is detected on the EXT pin causes the free-running internal 16-bit up-counter to increment starting from 0
  • The 16-bit reset counter value in each sensor sample provides a mechanism to determine the relative time delay from the most recent GNSS 1PPS pulse
  • When the init parameter time_correction is enabled (including ext_sel set to reset counter & count_out enabled)

    • The ROS driver attempts to correct the time stamp field in sensor_msgs/Imu based on the reset counter value (measured delay since latest GNSS 1PPS)

    • This should give a more accurate timestamp of the inertial data by minimizing the effects of link delays or host processing overhead delays

Building & Installing ROS1 Node

1. Place this package (including folders) into a new folder within your catkin workspace "src" folder.

  • For example, we recommend using the folder name "ess_imu_ros1_uart_driver"


2. Modify the CMakeLists.txt to select the desired Epson IMU model that is being used in the ROS system.

  • Refer to the comment lines inside the CMakeLists.txt for additional info.

  • NOTE: You *MUST* re-build using catkin_make when changing IMU models or any changes in the CMakeLists.txt

3. From the catkin workspace folder run "catkin_make" to build all changed ROS1 packages located in the <catkin_workspace>/src/ folder.

  • Re-run the above "catkin_make" command to rebuild the driver after making any changes to the CMakeLists.txt (or any of the .c or .cpp or .h source files)

  • *NOTE:* It is recommended to change IMU settings by editing the parameters in the launch file, wherever possible, instead of modifying the .c or .cpp source files directly


Example console output of catkin build for G370PDF1

user@user-VirtualBox:~/catkin_ws$ catkin_make
Base path: /home/user/catkin_ws
Source space: /home/user/catkin_ws/src
Build space: /home/user/catkin_ws/build
Devel space: /home/user/catkin_ws/devel
Install space: /home/user/catkin_ws/install
#### Running command: "cmake /home/user/catkin_ws/src -DCATKIN_DEVEL_PREFIX=/home/user/catkin_ws/devel -DCMAKE_INSTALL_PREFIX=/home/user/catkin_ws/install -G Unix Makefiles" in "/home/user/catkin_ws/build"
-- Using CATKIN_DEVEL_PREFIX: /home/user/catkin_ws/devel
-- Using CMAKE_PREFIX_PATH: /home/user/catkin_ws/devel;/opt/ros/kinetic
-- This workspace overlays: /home/user/catkin_ws/devel;/opt/ros/kinetic
-- Using PYTHON_EXECUTABLE: /usr/bin/python
-- Using Debian Python package layout
-- Using empy: /usr/bin/empy
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /home/user/catkin_ws/build/test_results
-- Found gmock sources under '/usr/src/gmock': gmock will be built
-- Found gtest sources under '/usr/src/gmock': gtests will be built
-- Using Python nosetests: /usr/bin/nosetests-2.7
-- catkin 0.7.14
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- ~~  traversing 1 packages in topological order:
-- ~~  - ess_imu_ros1_uart_driver
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- +++ processing catkin package: 'ess_imu_ros1_uart_driver'
-- ==> add_subdirectory(ess_imu_ros1_uart_driver)
-- Boost version: 1.58.0
-- Found the following Boost libraries:
--   system
---- Building for IMU Model: G370PDF1
-- Configuring done
-- Generating done
-- Build files have been written to: /home/user/catkin_ws/build
#### Running command: "make -j2 -l2" in "/home/user/catkin_ws/build"
Scanning dependencies of target ess_imu_ros1_uart_driver
[ 11%] Building C object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver.dir/src/hcl_gpio.c.o
[ 22%] Building C object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver.dir/src/hcl_linux.c.o
[ 44%] Building C object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver.dir/src/sensor_epsonCommon.c.o
[ 44%] Building C object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver.dir/src/hcl_uart.c.o
[ 55%] Building C object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver.dir/src/sensor_epsonUart.c.o
[ 66%] Building C object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver.dir/src/sensor_epsonG370.c.o
[ 77%] Linking C shared library /home/user/catkin_ws/devel/lib/
[ 77%] Built target ess_imu_ros1_uart_driver
Scanning dependencies of target ess_imu_ros1_uart_driver_node
[ 88%] Building CXX object ess_imu_ros1_uart_driver/CMakeFiles/ess_imu_ros1_uart_driver_node.dir/src/epson_imu_uart_driver_node.cpp.o
[100%] Linking CXX executable /home/user/catkin_ws/devel/lib/ess_imu_ros1_uart_driver/ess_imu_ros1_uart_driver_node
[100%] Built target ess_imu_ros1_uart_driver_node

4. Reload the current ROS1 environment variables that may have changed after the catkin build process.

<catkin_workspace>/source devel/setup.bash

5. Modify the appropriate roslaunch/XML to set your desired IMU init parameters for the specific IMU model in the launch folder that you selected and built

  • Typically, only the dout_rate & filter_sel needs to be edited

Running the ROS1 Node

  • To start the Epson IMU ROS1 driver use the appropriate launch file (located in launch/) with roslaunch

  • For example, for the Epson G370 IMU:

<catkin_workspace>/roslaunch ess_imu_ros1_uart_driver epson_g370.launch

Example console output of launching ROS1 node for G370PDF1

user@user-VirtualBox:~/catkin_ws$ roslaunch ess_imu_ros1_uart_driver epson_g370.launch
... logging to /home/user/.ros/log/86d27c9a-09bc-11eb-9ac8-080027cb8bd1/roslaunch-user-VirtualBox-4076.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://user-VirtualBox:35841/


 * /ess_imu_ros1_uart_driver_node/accel_bit: 1
 * /ess_imu_ros1_uart_driver_node/accel_delta_bit: 1
 * /ess_imu_ros1_uart_driver_node/accel_delta_out: 0
 * /ess_imu_ros1_uart_driver_node/accel_out: 1
 * /ess_imu_ros1_uart_driver_node/atti_bit: 1
 * /ess_imu_ros1_uart_driver_node/atti_out: 0
 * /ess_imu_ros1_uart_driver_node/checksum_out: 1
 * /ess_imu_ros1_uart_driver_node/count_out: 1
 * /ess_imu_ros1_uart_driver_node/dout_rate: 9
 * /ess_imu_ros1_uart_driver_node/drdy_on: 0
 * /ess_imu_ros1_uart_driver_node/drdy_pol: 0
 * /ess_imu_ros1_uart_driver_node/ext_pol: 0
 * /ess_imu_ros1_uart_driver_node/ext_sel: 0
 * /ess_imu_ros1_uart_driver_node/filter_sel: 9
 * /ess_imu_ros1_uart_driver_node/flag_out: 1
 * /ess_imu_ros1_uart_driver_node/gpio_out: 0
 * /ess_imu_ros1_uart_driver_node/gyro_bit: 1
 * /ess_imu_ros1_uart_driver_node/gyro_delta_bit: 1
 * /ess_imu_ros1_uart_driver_node/gyro_delta_out: 0
 * /ess_imu_ros1_uart_driver_node/gyro_out: 1
 * /ess_imu_ros1_uart_driver_node/invert_xaccel: 0
 * /ess_imu_ros1_uart_driver_node/invert_xgyro: 0
 * /ess_imu_ros1_uart_driver_node/invert_yaccel: 0
 * /ess_imu_ros1_uart_driver_node/invert_ygyro: 0
 * /ess_imu_ros1_uart_driver_node/invert_zaccel: 0
 * /ess_imu_ros1_uart_driver_node/invert_zgyro: 0
 * /ess_imu_ros1_uart_driver_node/port: /dev/ttyUSB0
 * /ess_imu_ros1_uart_driver_node/temp_bit: 1
 * /ess_imu_ros1_uart_driver_node/temp_out: 1
 * /ess_imu_ros1_uart_driver_node/time_correction: 0
 * /rosdistro: kinetic
 * /rosversion: 1.12.14

    ess_imu_ros1_uart_driver_node (ess_imu_ros1_uart_driver/epson_imu_uart_driver_node)

auto-starting new master
process[master]: started with pid [4086]

setting /run_id to 86d27c9a-09bc-11eb-9ac8-080027cb8bd1
process[rosout-1]: started with pid [4099]
started core service [/rosout]
process[ess_imu_ros1_uart_driver_node-2]: started with pid [4113]
[ INFO] [1602199089.860563057]: Initializing HCL layer...
[ INFO] [1602199089.860739911]: Initializing GPIO interface...
[ INFO] [1602199089.860788758]: Initializing UART interface...
Attempting to open port.../dev/ttyUSB0

...sensorDummyWrite.[ INFO] [1602199090.122510210]: Checking sensor NOT_READY status...
...done.[ INFO] [1602199091.016903361]: Initializing Sensor...
[ INFO] [1602199091.058212107]: Epson IMU initialized.
[ INFO] [1602199091.122874894]: PRODUCT ID:     G370PDF1
[ INFO] [1602199091.186292139]: SERIAL ID:      X0000002

...Sensor start.[ INFO] [1602199091.187993504]: Quaternion Output: Native.

USB-UART Latency

  • When using USB-UART bridge ICs to connect between the Linux host & Epson IMU, it is possible to experience higher than expected latencies or slower than expected IMU data rates

  • This could be caused by the USB-UART bridge device driver software which sets the default latency_timer too large (i.e. typically 16msec)
  • There are 2 recommended methods to reduce this value to 1msec to improve the latency & IMU publishing data rate

Modify latency_timer by sysfs mechanism

  • The example below reads the latency_timer setting for /dev/ttyUSB0 which returns 16msec
  • Then, the latency_timer is set to 1msec, and confirmed by readback.
  • NOTE: May require root (sudo su) access on your system to modify.

cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
echo 1 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

Modify low_latency flag using setserial utility

  • The example below sets the low_latency flag for /dev/ttyUSB0.
  • This will have the same effect as setting the latency_timer to 1msec.
  • This can be confirmed by running the setserial command again.
  • NOTE: You may need to install setserial with sudo apt install setserial

user@user-VirtualBox:~$ setserial /dev/ttyUSB0
/dev/ttyUSB0, UART: unknown, Port: 0x0000, IRQ: 0

user@user-VirtualBox:~$ setserial /dev/ttyUSB0 low_latency

user@user-VirtualBox:~$ setserial /dev/ttyUSB0
/dev/ttyUSB0, UART: unknown, Port: 0x0000, IRQ: 0, Flags: low_latency

Technical Support

  • Thank you for your interest and efforts in evaluating the Epson product

* For technical support or related issues using this ROS software with a supported Epson product, please email

Wiki: ess_imu_ros1_uart_driver (last edited 2022-08-03 16:49:59 by RChow)