Epson IMU ROS2 Node SPI ** Deprecated **

*** NOTE: This package has been superceded by Epson IMU ROS2 Driver Node***

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

Overview

• The Epson IMU ROS software is C++ wrapper around a C Linux driver for communicating on a ROS2 system

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

• This code assumes that the user is familiar with building ROS2 packages using the colcon build process
• This is *NOT* detailed step by step instructions describing how to build and install this ROS2 driver

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

SPI Connection & Configuration

• Since SPI interfaces are non-standard on PCs, typically IMU SPI interfacing is applicable only to embedded Linux platforms
• When connecting the Epson device to a ROS2 system using the SPI interface:
  • direct connection to SPI port must be compatible with CMOS 3.3V I/O

  • connection between the host & Epson device is possible using the M-G32EV031 evaluation breakout board

• This ROS2 driver uses the external library Unofficial wiringPi library to generate low level SPI communication & accurate time delays

  • Other libraries can be used to generate timer delays and SPI messages but requires minor changes to redirect the low-level function calls (i.e. bcm2835 C library, etc)

• Accurate timing delays are necessary to optimize throughput for high dout_rate when using the SPI interface (refer to IMU datasheets for timing specifications)

Below is an example IMU SPI connection when using a Raspberry Pi:

• Epson IMU	Raspberry Pi
  EPSON_RESET Input	RPI_GPIO_P1_15 (GPIO22) Output
  EPSON_DRDY Output	RPI_GPIO_P1_18 (GPIO24) Input
  EPSON_CS Input	RPI_GPIO_P1_16 (GPIO23) Output
  EPSON_SCLK Input	RPI_GPIO_P1_23 (GPIO11) Output
  EPSON_DOUT Output	RPI_GPIO_P1_19 (GPIO10) Input
  EPSON_DIN Input	RPI_GPIO_P1_21 (GPIO9) Output

Support for Timer Delays

• There are wrapper functions for time delays in millisecond and microseconds using seDelayMS() and seDelayMicroSecs(), respectively.

• On embedded Linux platforms, these may need to be redirected to platform-specific HW delay routines if not using a RaspberryPi

• For example on RaspberryPi, the time delay functions for millisecond and microseconds is redirected to WiringPi library delay() and delayMicroseconds() function calls, respectively.

• If a hardware delay is not available from a library, then a software delay loop is possible, but not preferred

Support for GPIO Control

• 3 GPIO pins on the host are designated used and should be connected to the IMU
  • GPIO output for asserting CS# on the IMU (NOTE: Not using pin SPI0_CE0)
  • GPIO output for asserting RESET# on the IMU
  • GPIO input for reading the logic status on the IMU DRDY (GPIO1) pin
• The use of GPIO pins for connecting to the IMU CS# and DRDY is mandatory
• RESET# is recommended to force Hardware Reset during every IMU initialization for better robustness.

ROS2 Node

• This ROS2 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

• 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

Launch File

• The launch file in the launch folder of this package is used to pass the init parameters to configure the IMU at runtime using ros2 launch

• Changes to init parameters by editing the launch file does not require rebuilding with colcon build

• 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 colcon build

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 (including ext_sel set to reset counter & count_out enabled)

  • The ROS2 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 ROS2 Node

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

2. Modify the CMakeLists.txt to select the desired Epson IMU model that is being used in the ROS2 system.

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

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

3. From the colcon workspace folder run "colcon build" to build all changed ROS2 packages located in the <colcon_workspace>/src/ folder.

4. Reload the current ROS2 environment variables that may have changed after the colcon build process.

From the <colcon_workspace>: . install/setup.bash

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

• Typically, only the imu_dout_rate & imu_filter_sel needs to be edited

Running the ROS2 Node

• To start the Epson IMU ROS2 driver use the appropriate launch file (located in launch/) with ros2 launch

• For example, for the Epson G370 IMU:

<colcon_workspace>/roslaunch ess_imu_ros2_spi_driver epson_g370.launch

Technical Support

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