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Epson IMU ROS1 Node UART ** Deprecated **

*** NOTE: This package has been superceded by Epson IMU ROS1 Driver Node***

*** This webpage will no longer be updated ***

Overview

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

  • Epson IMU SPI or UART Linux User-space Driver Example

• 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 README.md inside the ROS package for more detailed up-to-date technical info on usage or Github repository

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

• This ROS driver publishes IMU messages as per REP 145 Conventions for IMU Sensor Drivers

• sensor_msgs/Imu - contains header, orientation, angular velocity and linear acceleration

Published Topics

• For IMU models that support quaternion output function the orientation field in sensor_msgs/Imu can update with valid data and publish on imu/data

• For IMU models that do not support quaternion output function the orientation field in sensor_msgs/Imu will not update with valid data and publish on imu/data_raw

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 is made by editing the launch file which does not require rebuilding with catkin_make

• Typically, the user only needs to modify imu_dout_rate & imu_filter_sel as needed based on system requirements

• Only use the specific IMU model launch file associated with the same IMU model built using catkin_make

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 the init parameter time_correction is enabled in unison with 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.

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

• 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. 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:

<catkin_workspace>/roslaunch ess_imu_ros1_uart_driver epson_g370.launch

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
16
echo 1 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
1

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

• For technical support or related issues using this ROS software with a supported Epson product, please email sensingsystem_support@ea.epson.com