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Introduction

Welcome to the firmware team! We’re glad to have you.

In this lesson we’ll be covering:

1. What firmware is

2. An overview of our firmware system

3. What our process for writing firmware is

Just a quick note before we jump into the content. All of our modules assume that you have some familiarity with programming, specifically the C language. You unfortunately won’t be able to do much until you have some familiarity with the language (specifically pointers, functions and structures).

C Language Resources:

• C Guide for Firmware

• Basic concepts of C

• Midnight sun specific Intro to C programming (Shoutout @Arshan Khanifar)

• Interactive tutorial - Learn-C.org. If you’ve programmed before in other languages before, the most important parts for our team are listed below:

  • Pointers

  • Structures

  • Function arguments by reference

  • Arrays and Pointers

  • Function Pointers

With that out of the way, let’s get started!

What’s firmware?

Software vs. Firmware

Software is a set of instructions that you run on a computer. For example, your favourite video game or code editor is software. It’s normally stored on your hard drive, then when you want to execute it, your operating system (Windows or Mac OS or Linux) will grab those instructions, put them into working memory (RAM), and execute those instructions.

Firmware is also a set of instructions, but instead of being stored on your hard drive, they’re stored forever in memory. As soon as the computer is powered on, it’ll start executing these base instructions.

In our firmware team, we work mainly on writing code for microcontrollers (think Arduino) that control electrical signals or monitor the solar car. Microcontrollers are essentially just computers but way cooler!

Why does it matter?

Firmware generally has a lot more restrictions than software. The processor we use isn’t (comparatively) very fast and there isn’t much memory available, so our code needs to be simple and not too demanding. We can get around this restriction by breaking the firmware into small projects and running it on different boards, each responsible for controlling a different part of the car. Breaking it down also helps us work on different projects in parallel.

Hardware and Firmware

Our team coexists with hardware and it is mandatory for you to be interested and willing to learn electronic basics. This is what makes firmware super cool! It isn’t just software and it isn’t just hardware. We bring life to PCBs and give our vehicle functionality.

Systems overview

Here’s a diagram of the car’s electrical system:

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If this scares you, don’t worry! It scares us too. Thankfully, implementing what’s in this diagram is the hardware team’s job, not ours!

Firmware system overview

See, we don’t even need to worry about wires. Much cleaner and easier to understand.

Each non-bolded line in the diagram represents a firmware project that controls a part of the car’s electrical system, grouped under the headings in bold. Here’s a quick rundown of what each firmware project does:

1. Battery: Ensures the battery doesn’t explode.

2. Driver controls: Takes input from the driver and passes it on to the rest of the system.

3. Power distribution: Turns other boards on and off (controls which boards are powered).

4. Drivetrain: Converts the angle that the pedal is at to the current levels for the motors (so if you floor it the car will go faster).

5. Charging: Manages charging of the battery from an off-the-shelf wall electric car wall charger or from the solar array.

Your PC vs a Microcontroller

We write all the code on our personal computers, but we need it to build it differently so that we can flash it over to run on our microcontrollers in a way that they understand. There are a few differences between the two that we need to consider.

Quick disclaimer: if this section doesn’t really make sense to you, that’s ok! You can still write code without it. But, this should help you understand what the difference is between working remotely and working directly with hardware.

First, let’s talk about compiling code.

Compiling code

As you may or may not know, to run C code, first you have to compile it. This means turning the higher level instructions you write as code into simpler instructions for the computer to understand.

An important caveat here is that not all computers understand the same instructions. For example, the processor in your laptop understands instructions called x86 (instruction set for Intel processors), while the computer chips we run our firmware on understands instructions called ARM.

Compiling our code

To do things like turn headlights on or off and read voltages from our hardware components on the BMS (battery management system) through code, we use pieces of code that are called libraries. Our firmware projects implement the logic parts we need, like determining when and how often we want an LED to blink and then we use the library to actually talk to the LED to turn it on or off. What this allows us to do is have different versions of the libraries for different types of computers:

This is the key to letting us work remotely! We can write all our C code and run it on our laptops, and never worry about actually touching the hardware, right?

Unfortunately, it’s not quite that simple. Some things are really hard to emulate on x86, especially things that are time-sensitive since you don’t know what else your laptop might be doing while you’re running the code. Microcontrollers have internal clocks which may differ from the one on your computer. However, it still gives us enough capability to write code and test our main logic.

Our Process

Writing Code

Our firmware runs in safety-critical situations, and as such it can be dangerous if it goes wrong. To help prevent this we have a structure for creating and testing our firmware.

1. High-level design: We come up with a high-level structure of the project that fulfils the requirement.

2. Detail design: we sort out the specifics, like what events or messages need to be passed between modules of the project

3. Implementation: we write the code.

4. Unit testing: we write tests that test specific parts of the code to make sure our logic works the way we think it does.

5. IO testing/Hardware validation: input/output testing. We run the project on hardware, and make sure the hardware works the way we expect it to.

6. Integration testing: we connect multiple boards together and make sure they work together the way we expect them to.

Notice how much testing we go through! This is really important. In firmware, writing the code is often only half the battle, and there can be many unforeseen delays when you actually start interacting with hardware.

Tools

GitHub:

Git is a version control system that lets us have a master version of our firmware code as well as “branches”. GitHub allows you to use git to Each branch can have modifications made to it in an isolated environment, then once the changes are checked and verified, they can be “merged” back into master. We use this as a way to give each member an isolated environment to work on their changes.

JIRA:

A project tracking tool that lets us easily keep track of all the tasks people are assigned to and their progress.

We put “tickets” on the board, which include the task, the assignee, and some other information about the task.

Conclusion

Thanks for sticking through! In conclusion, here’s what you should come away from reading this with an understanding of:

1. What firmware is

2. What our firmware systems do at a high level

3. How we’re able to work on firmware without direct access to the hardware

4. Our process for completing firmware projects

Next in firmware 102, we’ll go into more depth on our firmware system, controller boards, our project structure, testing and validation, and our collaboration platforms. We hope to see you there!

FW 101 Tasks

Each of these modules comes with some tasks or projects that should be completed before moving onto the next part. There will usually be a deliverable so that we can check off that you’ve completed the homework.

*One important thing: as you are working through your tasks, you will encounter errors. The leads are happy to answer questions about any of these issues, but most of the time it can be solved by a quick google. 90% of the errors you will encounter can usually be solved with answers from Stack Overflow, and a little bit of thinking.

FW 101 Tasks

There are several tasks that need to be completed as part of this module:

1. Learn about Git and the Command Line by watching/reading the following tutorials

   1. Git Tutorial Videos (part 1 and 2) and branching lesson

   2. Command Line Tutorials (Part 1 and 2)

2. Get your environment set up by following the instructions listed at Setup

3. Write your very own Hello World program!

1. Intro Videos

These videos give an introduction to two of the main tools we use on our team, Git and the shell command line. We suggest watching them if you aren’t very experienced in one or the other, since the rest of the onboarding content will rely heavily on these concepts. However, we also do explain it as we go, so feel free to continue on even if you still haven’t fully grasped the concepts, and use these resources when you get stuck.

2. Setup

Assuming you have followed the steps listed in the setup page, we can now try out your new repository.

Once you’ve got your box set up (you should be in the vagrant environment. If you type whoami in your console it should print vagrant below) and have pulled the fwxv repository, we can build and run it on the x86 platform.

We use SCons to compile and build our software. It is generally invoked with arguments which tells it how and what to build. You should now run the following command in your command line; this will build and then run our “leds” program.

You will see a bunch of build output printed to your screen, and then a periodic printing of the word “blink”, something like below:

Don’t worry about what anything means, this is just to make sure you’ve got things up and running. We will talk more about scons and building software later.

3. Hello World

This section will cover writing a basic hello world program (using the C language), and running it in the environment we have just set up.

Let’s take a quick look at our fwxv repository before we get started. Type ls in your command line (at the fwxv directory) to list the directory contents. You should see something like the image below:

The two main things we care about right now are the projects and libraries items. These are directories, which hold the firmware we write.

Libraries contains the code that is standalone, to be included the main programs we write, using #include "library.h". Some of these libraries we write ourselves, some of them (such as the FreeRTOS source code) we get from other sources. Each library will generally consist of a header file (.h) and a C-file (.c). The header file holds any new data types which are used in library, and declarations for functions the library may provide, and other useful information. The .c file contains the definitions for these functions.

The projects directory is where we write and build our main software which will run. If you are familiar with C programs, you know that they have a “main” function which is where the program starts when it runs. This is in a main.c file for all our projects. The projects directory is where the main file and any other project-specific software lives.

We will start by creating a new project where we will write our hello world program. Luckily, we can run the following command to do it for us! Make sure you are in the fwxv directory, this is where all commands must be called from.

This will create a new project with the name “hello_world”. We can view it by listing the projects directory with ls projects. It should look something like this

As you can see, there were already a few projects existing, including the leds one that we built and ran earlier. Each project is a directory as well, with the file structure shown below.

The main file and any other .c files go in the src/ directory, and any header files go in the inc/ directory. The readme is a text file where you can give a description of your project, and the config.json is needed for including external libraries, but we will get to that later.

We need to create a main.c file in our src directory. You can do this from the command-line, or you can open up the fwxv folder in your favourite text editor and do it there (If you don’t have one, VS Code is recommended, but it doesn’t really matter). We then need to open our main.c file for editing.

A C program is comprised of the following main components.

As you can see, we have a simple program which increments an integer and stores its value in a buffer array. Using this template, we are now going to write our very own hello world program!

The Program

The goal of this next part is to write a program which increments an integer using a function, and prints it to the console every second along with “Hello world”.

You will need to use a few things from our code base for this project.

1. Include the “log.h” library. We have our own version of printf which allows us to safely print to the console. You can use it the exact same way as printf, just replacing it with LOG_DEBUG, ie:
   LOG_DEBUG("Hello World %d\n", my_int);

Run the program using the scons command from above (with a different project name).This program should run forever in a while true loop.

When you are done, take a screenshot of your output or bring your computer over and show it to a lead. You are officially done FW 101, Congrats!