Mastering Embedded Linux: Understanding Platform Daemons

This is the fifth installment of the Mastering Embedded Linux series, designed to help develop affordable, tailored Linux systems for embedded devices. Previously, this series covered an overview of the Linux landscape and tutorials on building firmware for the Raspberry Pi using Buildroot.

In this article, I focus on how to leverage Buildroot skills to package custom software into embedded firmware. Specifically, I introduce the concept of a “platform daemon” and demonstrate its implementation in Rust. The next part will guide you through creating a package to include this software in Buildroot.

What Are Platform Daemons?

Most of this series has used pre-existing embedded software, including the Buildroot distribution itself and its packages. However, each embedded system often requires specific software — a “secret sauce” — tailored for its unique hardware and functions.

A common pattern is a custom piece of software that extends the kernel’s capabilities, especially for managing data transfer between peripherals. Although the kernel provides drivers for devices like ADCs (analog-to-digital converters), it doesn’t handle data routing or communication. For example, if an ADC needs to send readings over USB, the kernel allows user-space programs to communicate with the hardware, but it’s up to custom software to read data from the ADC and send it via USB.

This specialized software is what I call a platform daemon. It’s custom-developed for a specific device or set of devices, managing hardware states and data flow. These daemons often contain device driver logic for peripherals that ideally should be part of the kernel, but instead run as user-space processes.

Overall, a platform daemon has deep system knowledge, oversees peripheral management, and routes communication between hardware components and higher-level applications. Its tailor-made nature makes it integral to the specific functions of an embedded platform, providing a bridge that complements the kernel’s core drivers.