We plan to explain how to design and write your own Bootloader for STM32 devices.Before we start writing code, we must first understand what a Bootloader is and why it is needed.This article will introduce you to the basic concepts of Bootloader.

Bootloader Basics

A Bootloader is a very important component of any operating system.

A Bootloader is also known as boot program or bootstrap loader.

It is a special type of operating system software that is loaded into working memory after the computer starts up.

So it is important to clarify: it is also a type of software, just like an application.

The term Bootloader is actually an abbreviation of “bootstrap loader”.

How Does a Bootloader Work?

Understanding how a Bootloader operates does not require you to be an embedded systems expert. Just having used the Windows operating system is sufficient.

When you power on your computer, have you noticed that some text appears on the screen before the Windows logo shows up?

During the boot process, if you press Shift or F12, you usually enter a blue options interface.

That’s right, that is the Bootloader.

The Bootloader performs some operations as needed. Once completed, it hands over control to the operating system (OS). Then the OS takes over the entire system operation.

Whether it is Windows, Mac, or Linux, all operating systems have a Bootloader, and they always run in the initial phase.

What Is a Bootloader in Embedded Systems?

In microcontrollers, the role of the Bootloader is similar to that of an operating system.

If there is a Bootloader in the device, it is the first code that runs when you press the reset button. If there is no Bootloader, the application will run directly.

If a Bootloader exists, it will run first and perform some initialization or checks. Once completed, it hands over control to the application, which then starts working according to the product or project requirements.

Why Do Microcontrollers Need a Bootloader?

1. Firmware Update

You might ask: is it really useful? Why do we need it?

I agree that without a Bootloader, the system would be simpler. We would only need one application, without the need to write an additional Bootloader.

But if you want to sell products, the situation is different. What if you have already sold the device to a customer, but later need to update the application/firmware?

You can’t possibly take a JTAG/J-LINK debugger to the customer’s site every time to reprogram the firmware, right? That is almost impossible to achieve.

With a Bootloader, you don’t have to worry about this issue. You can update the firmware without connecting a debugger or downloader.

2. Security

If your product requires security, the Bootloader can also play a role.

For example: what if someone maliciously replaces the application or firmware in the device with homemade firmware to compromise your product? How do you detect such tampering?

In this case, the Bootloader can be used to verify the legitimacy of the firmware. Only if the verification passes will it hand over control to the application.