Software Requirements Specification for DEV1 Inertial Measurement Unit

Introduction

Purpose

The purpose of this document is to detail the software requirements and constraints for the firmware of the Dirt Electric Vehicle 1 Inertial Measurement Unit (DEV1 IMU). This document will go into detail on the requirements necessary for the system as well as detailing the constraints that the system will be under. The intention is that this document will provide a means to holistically express the needs of the DEV1 IMU system.

Document Conventions

This document was created based on the IEEE template for software requirements specifications. As such it will mainly adhere to the verbiage and style set by IEEE convention. Additionally, a glossary has been provided in the Appendix which covers common phrases that will be used in this document.

Intended Audience and Reading Suggestions

The intention is that this document will be accessible across engineering disciplines. The DEV1 IMU represents a highly inter-disciplinary project on the RIT Electric Vehicle Team and as such this document should be accessible to all involved. Below is a breakdown of the intended audiences and how they may use the document. This list is not exhaustive, but intended to guide common readers of this document.

• Electrical Team Members: Members of the electrical team who are designing and building the DEV1 IMU. Members of this group may refer to this document to ensure requirements and constraints align with their expectations. Additionally, this document can be used as a point of reference during the hardware/firmware bringup process.

• Firmware Team Members: Developers on the firmware team who are designing, developing, and testing the DEV1 IMU firmware. Members of this team will need to refer to this document throughout the development process to ensure all target needs are met within the agreed upon constraints.

• Integration Team Members: RIT EVT team members who handle systems-level integration on the team. These team members may use this document to gain and understanding of how the DEV1 IMU will operate. Most critically, how the DEV1 IMU will operate within the structure of the DEV1 architecture.

The document is laid out where it is not strictly necessary to read all sections in their entirety. Instead each section should be self-contained and comprehensive within its scope. As such audience members are encouraged to read the sections that most pertain to their needs. Additionally, the glossary in the Appendix may prove useful in situations where phrases may be used in specific ways within this document.

Product Scope

The DEV1 IMU measures inertial data for the DEV1 bike. The DEV1 IMU reports its measurements over the DEV1 CAN network for other boards to act accordingly for optimal performance.

Overview

The rest of this software design document will go further into the specifics of the requirements while also looking at the constraints of the system. The goal is to clarify the use cases of the DEV1 IMU and to specify what the DEV1 IMU will do in those cases. Design considerations will not be discussed, however notable design constraints will be covered.

Overall Description

Product Perspective

The DEV1 IMU plays a role in performance optimization for the DEV1 bike. It reports measurements such as linear/angular acceleration and Euler angle over the bike’s CAN network, allowing other boards to adjust their behaviors to maintain the best performance.

The DEV1 IMU is made up of two primary components, the STM32F334K8 microcontroller and the BNO055 orientation sensor chip. The ST microcontroller handles processing of data and manages CAN network communication for the IMU. The BNO055 is used to obtain the orientation measurements.

Currently, the IMU data is not being used by other boards, but can be used for traction control in the future.

User Interfaces

Users will rarely interact directly with the DEV1 IMU software. The DEV1 IMU software will mainly be interfaced with via CANopen and thus will require additional tools to interact with the DEV1 IMU. There is no current plan for a team-developed tool to provide an interface for interaction with the DEV1 IMU.

Hardware Interfaces

The DEV1 IMU is connected to the bike’s CANopen network which is made up of a two-wire differential pair. The board also features a JTAG connector that exposes an SWD interface for programming and a UART interface for communicating directly with the microcontroller.

Software Interfaces

The DEV1 IMU software reports of measurements over the CANopen network. Note that the behavior of the IMU cannot be modified over CANopen.

Communication Interfaces

The DEV1 IMU communicates over the CANopen network to broadcast its data to other boards.

Communication between the STM32F334r8 microcontroller and the BNO055 are handled via I2C, however it does not adhere to standard I2C. For more about the non-standard I2C communication scheme, read (WIP, will include I2C implementation detail in the State of the Software doc)

Memory Constraints

The produced software is limited to the 64KB of flash memory that is available on the STM32F334r8. Therefore the resulting binary must fit within this size.

Operations

The DEV1 IMU’s main operation is to relay data measured by the BNO055 sensor to the rest of the bike through the CANopen network. This includes initialization and configuration of the BNO055 chip, and managing the CANopen network communication.

Site Adaptation

The DEV1 IMU is intended specifically for the DEV1 system. Therefore, the software requirements and design will center around the specifics of the DEV1 system. No additional adaptations are currently being considered.

Initialization and Configuration of BNO055

One of the main components of the DEV1 IMU is the BNO055 chip, which requires proper initialization and configuration before it will collect data. The following procedure is informed by the BNO055’s datasheet which details correct usage of the chip. After establishing I2C connection with the chip, the driver class will:

• check that the BNO055’s self-test initiated at startup was successful

• switch the BNO055 from configuration mode to NDOF operation mode

The NDOF operation mode calculates fused absolute orientation data from the accelerometer, gyroscope and magnetometer. More information can be found in the BNO055 datasheet.

Notification of BNO055 Data

The BNO055 will collect the following data in 3D space (X,Y,Z):

• Euler angles

• gyroscope measurements

• linear acceleration

• accelerometer measurements

The data is broadcast on the CANopen network for other boards to read.

User Classes and Characteristics

The IMU chip is an auxiliary board that does not require any user interaction post-development.

Operating Environments

The software will operate on the ST microcontroller present on the DEV1 IMU. The software environment is embedded with no operating system present. All development will take place through the EVT-core library and will interact directly with the ST microcontroller.

User Documentation

Additional documentation will need to exist for boards that will react to the DEV1 IMU’s reported data. Information for each board will need to include which data it will use and how it will adjust itself accordingly. This will provide users with a holistic view of how the DEV1 IMU is used in the bike.

Constraints

Below are some constraints worth considering. They are a fixed part of the system.

• Development must be in C/C++

• Communication will take place using CANopen

• EVT-core will be used for low level microcontroller interfacing

• Must be developed for the STM32F334r8

• Resulting binary must fit within the ST microcontroller 64KB flash memory

• Orientation measurements must be performed by the BNO055

• Non-standard I2C communication with the BNO055

Assumptions and Dependencies

It is assumed that the BNO055 chip will behave exactly as described by its datasheet, unless communication between the BNO055 chip and ST microcontroller fails.

Apportioning of Requirements

At this point in the life cycle of the DEV1 IMU project, deployment has begun. Due to the nature of student-run teams, it is unlikely that there will be further revision to this system, as new students will likely start new projects. As a result, there are no future requirements planned to be added to this system.

Specific Requirements

External Interface Requirements

• no external interface

Functions

The DEV1 IMU follows a specific procedure for proper initialization and configuration of the BNO055 chip. A general outline of what the system shall do is described in the Product Functions section under Initialization and Configuration of BNO055.

Appendix

Glossary

Term	Definition
IMU	Inertial Measurement Unit
CAN	Controller Area Network
CANopen	Higher-level communication protocol using CAN
DEV1	Dirt Electric Vehicle 1
EVT	Electric Vehicle Team
I2C	Inter-Integrated Circuit
KB	Kilobyte
STM32F334K8	ST Microcontroller selected for this project

References

• BNO055 Intelligent 9-axis absolute orientation sensor

• CANopen - The standardized embedded network

• EVT-core

• STM32F334K8 Mainstream Mixed signals MCUs Arm Cortex-M4 core with DSP and FPU, 64 Kbytes of Flash memory, 72 MHz CPU, CCM, 12-bit ADC 5 MSPS, comparators, op-amp, hr timer

Revision

Revision	Description	Date
1	Initial documentation.	2/4/2025