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*** NOTE: This package has been superceded by Epson IMU ROS1 Driver Node***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

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_spi_driver epson_g370.launch

Technical Support

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