README for Epson IMU Driver for ROS1 Node

• README for Epson IMU Driver for ROS1 node
  • What is this repository for?
  • What kind of hardware or software will I likely need?
    • For the UART Interface:
    • For the SPI Interface:
  • How do I use the driver?
  • How do I use the driver if usleep() is not supported for time delays?
  • How do I use the driver with GPIOs to control IMU RESET#, DRDY, EXT pins?
  • How do I build, install, run this package?
    • Example console output of catkin_make build:
    • Example console output of launching ROS node:
  • What does this ROS IMU Node publish as messages?
    • ROS Topic Message /imu/data
    • ROS Topic Message /imu/data_raw
  • Why am I seeing inaccurate ROS timestamps, high latencies, or slower than expected IMU data rates?
    • ROS timestamps
    • When using USB-UART bridges
      • Modifying latency_timer by udev mechanism
      • Modifying latency_timer by sysfs mechanism
      • Modifying low_latency flag using setserial utility
    • When using the SPI interface
  • Package Contents
  • References

What is this repository for?

• This code is a ROS1 package for demonstrating a ROS node that configures and publishes IMU messages from a supported Epson IMU.
• This code provides software communication between Epson IMU and ROS using the either the UART or SPI interface.
• For the UART connection, this code uses the standard Unix Terminal I/O library (termios) for communicating either direct or by USB-serial converter such as FTDI USB-UART bridge ICs.
• For the SPI connection, this code uses the Unofficial wiringPi library for accessing GPIO and SPI functions on the Raspberry Pi platform running Ubuntu Linux distro.
• This ROS1 node demonstration software is a ROS C++ wrapper around the Linux C driver software:
  • src/epson_imu_uart_ros_node.cpp is for the UART interface
  • src/epson_imu_spi_ros_node.cpp is for the SPI interface
• The other source files in src/ are based on the Linux C driver originally released and can be found here: Linux C driver and logger example for EPSON IMU
• Information about ROS, and tutorials can be found: ROS.org

What kind of hardware or software will I likely need?

• Epson IMU Epson IMU models
  • At the time software release:
    • G320PDG0, G320PDGN, G354PDH0, G364PDCA, G364PDC0
    • G365PDC1, G365PDF1, G370PDF1, G370PDS0
    • G330PDG0, G366PDG0, G370PDG0, G370PDT0
    • G570PR20
• ROS Noetic (via download) ROS.org
• This software was developed and tested on the following:

  ROS1:        Noetic
  Description: Ubuntu 20.04 LTS
  Hardware Platform: Core i7 PC, Raspberry Pi 3B+, RaspberryPi 4

For the UART Interface:

• Epson USB evaluation board or equivalent FTDI USB-Serial interface connecting the Epson IMU to ROS host (tty/serial) See M-G32EV041
• Alternatively, a direct connection from the Epson IMU to the ROS platform supporting a 3.3V CMOS compatible UART interface See M-G32EV031.

For the SPI Interface:

• NOTE: This software is intended for an embedded Linux host system with 3.3V I/O compatible SPI interface (SCLK, MISO, MOSI) and 3 GPIOs (CS#, RST#, DRDY).
• For Raspberry Pi, if not enabled already the SPI interface can be enabled using raspi-config or equivalent.
• This code uses a separate GPIO to manually control CS# chipselect instead of the chipselect assigned to by the RapsberryPi SPI interface.
  • The chipselect assigned by the HW SPI interface should also work, but has not been thoroughly tested.
• Epson Breakout evaluation board or some equivalent is required to connect to the 3.3V CMOS compatible pins of the ROS host (SPI & GPIOs) See M-G32EV031

How do I use the driver?

• This code assumes that the user is familiar with building ROS packages using the catkin_make build process.

• This README is NOT detailed step by step instructions on how to build and install ROS software.

• Please refer to the ROS.org website for more detailed instructions on the ROS package build process. ROS.org

• NOTE: At a bare minimum, the user must re-build the package with catkin_make after modifying the CMakeLists.txt to configure any of the following:

  • serial interface type, INTERFACE= (UART or SPI)
  • host platform type, PLATFORM= (RPI or NONE=PC)

• Changes to IMU settings should be made by editing the .launch files located in the launch/ folder instead of modifying the src/ source files

How do I use the driver if usleep() is not supported for time delays?

• NOTE: In the hcl_linux.c or hcl_rpi.c, there are seDelayMS() and seDelayMicroSecs() wrapper functions for time delays in millisecond and microseconds, respectively.
• On embedded Linux platforms, the user may need to modify and redirect to platform specific delay routines if usleep() is not supported.
• For example on RaspberryPi, the time delay functions for millisecond and microseconds are redirected to WiringPi library delay() and delayMicroseconds(), respectively.
• If a hardware delay is not available from a library, then a software delay loop is possible but not preferred.

How do I use the driver with GPIOs to control IMU RESET#, DRDY, EXT pins?

• When connecting the IMU using the UART interface, the use of GPIO pins for connecting to the IMU RESET# or DRDY is optional, but can be useful on an embedded Linux platforms (such as RapsberryPi).
• When connecting the IMU using the SPI interface, the use of GPIO pins for connecting to the IMU DRDY is mandatory (RESET# is recommended, EXT is optional).
• When using the time_correction function for accurate time stamping with an external 3.3V GNSS 1PPS signal, the IMU EXT pin must be connected to the 1PPS.

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