Name: Embedded Systems Architecture - Second Edition (Daniele Lacamera) (z-library.sk, 1lib.sk, z-lib.sk)
Author: Unknown Author

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Table of Contents Preface Part 1 – Introduction to Embedded Systems Development Chapter 1: Embedded Systems – A Pragmatic Approach Chapter 2: Work Environment and Workflow Optimization Part 2 – Core System Architecture Chapter 3: Architectural Patterns Chapter 4: The Boot-Up Procedure Chapter 5: Memory Management Part 3 – Device Drivers and Communication Interfaces Chapter 6: General-Purpose Peripherals Chapter 7: Local Bus Interfaces Chapter 8: Power Management and Energy Saving Chapter 9: Distributed Systems and IoT Architecture Part 4 – Multithreading Chapter 10: Parallel Tasks and Scheduling Chapter 11: Trusted Execution Environment Index Other Books You May Enjoy

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Preface Embedded systems have become increasingly popular in the last two decades thanks to the technological progress made by microelectronics manufacturers and designers, which has aimed to increase computing power and decrease the size of the logic of microprocessors and peripherals. Designing, implementing, and integrating the software components for these systems requires a direct approach to the hardware functionalities in most cases, where tasks are implemented in a single thread and there is no operating system to provide abstractions to access CPU features and external peripherals. For this reason, embedded development is considered a domain on its own in the universe of software development, in which the developer’s approach and workflow need to be adapted accordingly. This book briefly explains the hardware architecture of a typical embedded system, introduces the tools and methodologies needed to get started with the development of a target architecture, and then guides the readers through interaction with the system features and peripheral interaction. Some areas, such as energy efficiency and connectivity, are addressed in more detail to give a closer view of the techniques used to design low-power and connected systems. Later in the book, a more complex design, incorporating a (simplified) real-time operating system, is built from the bottom up, starting from the implementation of single system components. Finally, in this second edition, we have added a detailed analysis of the implementation of TrustZone-M, the TEE technology introduced by ARM as part of its latest family of embedded microcontrollers.

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The discussion often focuses on specific security and safety mechanisms by suggesting specific technologies aimed at improving the robustness of the system against programming errors in the application code, or even malicious attempts to compromise its integrity.

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Who this book is for If you’re a software developer or designer that wants to learn about embedded programming, this is the book for you. You’ll also find this book useful if you’re a less experienced or a beginner embedded programmer willing to expand your knowledge of embedded systems. More experience embedded software engineers may find this book useful for refreshing their knowledge of the internals of device drivers, memory safety, secure data transfers, privilege separation, and secure execution domains.

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What this book covers Chapter 1, Embedded Systems – A Pragmatic Approach, is an introduction to microcontroller-based embedded systems. The scope of the book is identified, from a broader definition of “embedded systems” to the actual domain that will be analyzed – 32-bit microcontrollers with physical memory mapping. Chapter 2, Work Environment and Workflow Optimization, outlines the tools used and the development workflow. This is an introduction to the toolchain, debuggers, and emulators that can be used to produce code in a binary format that can be uploaded and run on the target platform. Chapter 3, Architectural Patterns, is all about the strategies and development methodologies for collaborative development and testing. This chapter proposes a description of the processes that are typically used while developing and testing software for embedded systems. Chapter 4, The Boot-Up Procedure, analyzes the boot phase of an embedded system, boot stages, and bootloaders. It contains a detailed description of the bring-up code and the mechanisms used to separate the software into several boot stages. Chapter 5, Memory Management, suggests some optimal strategies for memory management by pointing out common pitfalls and explaining how to avoid memory errors that can result in unpredictable or bad behavior in the application code. Chapter 6, General-Purpose Peripherals, walks through accessing GPIO pins and other generic integrated peripherals. This is the first interaction of the target platform

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with the outside world, using electric signals to perform simple input/output operations. Chapter 7, Local Bus Interfaces, guides you through the integration of serial bus controllers (UART, SPI, and I2C). A code-oriented, detailed analysis of the most common bus communication protocols is introduced by explaining the code required to interact with the transceivers commonly available in embedded systems. Chapter 8, Power Management and Energy Saving, explores the techniques available to reduce power consumption in energy-efficient systems. Designing low-power and ultra- low-power embedded systems requires specific steps to be performed for reducing energy consumption while running the required tasks. Chapter 9, Distributed Systems and IoT Architecture, introduces the available protocols and interfaces required to build distributed and connected systems. IoT systems need to communicate with remote endpoints using standard network protocols that are implemented using third-party libraries. Particular attention is dedicated to securing communication between endpoints using secure sockets. Chapter 10, Parallel Tasks and Scheduling, explains the infrastructure of a multitasking operating system through the implementation of a real-time task scheduler. This chapter proposes three approaches for implementing operating systems for microcontrollers from scratch, using different schedulers (cooperative, pre-emptive, and safe). Chapter 11, Trusted Execution Environment, describes the TEE mechanisms typically available on embedded systems and provides an example of running secure and non-secure domains using ARM TrustZone-M. On modern

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microcontrollers, TEE provides the opportunity to secure specific areas of memory or peripherals by limiting their access from the non-secure execution domain. To get the most out of this book It is expected that you are proficient in the C language and understand how computer systems work. A GNU or Linux development machine is required to apply the concepts explained. Going through the example code provided is sometimes necessary to fully understand the mechanisms implemented. You are encouraged to modify, improve, and reuse the examples provided, applying the suggested methodologies. Additional usage instructions for the requested tools are available in Chapter 2, Work Environment and Workflow Optimization. If you are using the digital version of this book, we advise you to type the code yourself or access the code from the book’s GitHub repository (a link is available in the next section). Doing so will help you avoid any potential errors related to the copying and pasting of code.

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Download the example code files You can download the example code files for this book from GitHub at https://github.com/PacktPublishing/Embedded- Systems-Architecture-Second-Edition. If there’s an update to the code, it will be updated in the GitHub repository. We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out! Download the color images We also provide a PDF file that has color images of the screenshots and diagrams used in this book. You can download it here: https://packt.link/kVMr1. Conventions used There are a number of text conventions used throughout this book. Code in text: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: “A single configuration file must be provided from the command-line invocation, with several platforms and development board configurations provided under the /scripts directory.”

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A block of code is set as follows: When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:    Secure Area 1:      SECWM1_PSTRT : 0x0  (0x8000000)      SECWM1_PEND  : 0x39  (0x8039000) Any command-line input or output is written as follows: Commands for the debugger console are written as follows:     > add-symbol-file app.elf 0x1000     > bt full Tips or important notes Appear like this. Get in touch Feedback from our readers is always welcome. General feedback: If you have questions about any aspect of this book, email us at customercare@packtpub.com and mention the book title in the subject of your message. Errata: Although we have taken every care to ensure the accuracy of our content, mistakes do happen. If you have   /* Jump to non secure app_entry */  asm volatile("mov r12, $ renode /opt/renode/scripts/single-node/stm32f4_discovery.re

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found a mistake in this book, we would be grateful if you would report this to us. Please visit www.packtpub.com/support/errata and fill in the form. Piracy: If you come across any illegal copies of our works in any form on the internet, we would be grateful if you would provide us with the location address or website name. Please contact us at copyright@packt.com with a link to the material. If you are interested in becoming an author: If there is a topic that you have expertise in and you are interested in either writing or contributing to a book, please visit authors.packtpub.com. Share your thoughts Once you’ve read Embedded Systems Architecture, Second Edition, we’d love to hear your thoughts! Please click here to go straight to the Amazon review page for this book and share your feedback. Your review is important to us and the tech community and will help us make sure we’re delivering excellent quality content. Download a free PDF copy of this book Thanks for purchasing this book! Do you like to read on the go but are unable to carry your print books everywhere?

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Part 1 – Introduction to Embedded Systems Development This part gives a bird’s eye view of embedded development, explaining how it differs from other technical fields that developers may be familiar with. The second chapter helps transform a developer’s workstation into an actual hardware/software development lab and optimizes the steps needed to develop, test, debug, and deploy embedded software. This part has the following chapters: Chapter 1, Embedded Systems – A Pragmatic Approach Chapter 2, Work Environment and Workflow Optimization

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Embedded Systems – A Pragmatic Approach Designing and writing software for embedded systems poses a different set of challenges than traditional high-level software development. This chapter provides an overview of these challenges and introduces the basic components and the platform that will be used as a reference in this book. In this chapter, we will discuss the following topics: Domain definition Embedded systems are computing devices that perform specific, dedicated tasks with no direct or continued user interaction. Due to the variety of markets and technologies, these objects have different shapes and sizes, but often, all have a small size and a limited amount of resources. In this book, the concepts and the building blocks of embedded systems will be analyzed through the Domain definition General-purpose input/output (GPIO) Interfaces and peripherals Connected systems Introduction to isolation mechanisms The reference platform

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development of the software components that interact with their resources and peripherals. The first step is to define the scope for the validity of the techniques and the architectural patterns explained in this book, within the broader definition of embedded systems. Embedded Linux systems One part of the embedded market relies on devices with enough power and resources to run a variant of the GNU/Linux OS. These systems, often referred to as embedded Linux, are outside the scope of this book, as their development includes different strategies of design and integration of the components. A typical hardware platform that is capable of running a system based on the Linux kernel is equipped with a reasonably large amount of RAM, up to a few gigabytes, and sufficient storage space on board to store all the software components provided in the GNU/Linux distribution. Additionally, for the Linux memory management to provide separate virtual address spaces to each process on the system, the hardware must be equipped with a memory management unit (MMU), a hardware component that assists the OS in translating physical addresses into virtual addresses, and vice versa, at runtime. This class of devices presents different characteristics that are often overkill for building tailored solutions, which can use a much simpler design and reduce the production costs of single units. Hardware manufacturers and chip designers have researched new techniques to improve the performance of microcontroller-based systems. In the past few decades, they have introduced new generations of platforms that

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would cut hardware costs, firmware complexity, size, and power consumption to provide a set of features that are most interesting for the embedded market. Due to their specifications, in some real-life scenarios, embedded systems must be able to execute a series of tasks within a short, measurable, and predictable amount of time. These kinds of systems are called real-time systems and differ from the approach of multi-task computing, which is used in desktops, servers, and mobile phones. Real-time processing is a goal that is extremely hard, if not impossible, to reach on embedded Linux platforms. The Linux kernel is not designed for hard real-time processing, and even if patches are available to modify the kernel scheduler to help meet these requirements, the results are not comparable to bare-metal, constrained systems that are designed with this purpose in mind. Some other application domains, such as battery-powered and energy-harvesting devices, can benefit from the low power consumption capabilities of smaller embedded devices and the energy efficiency of the wireless communication technologies often integrated into embedded connected devices. The higher amount of resources and the increased hardware complexity of Linux- based systems often do not scale down enough on energy levels or require effort to meet similar figures in power consumption. The type of microcontroller-based systems that we will analyze in this book is 32-bit systems, which are capable of running software in a single-threaded, bare-metal application, as well as integrating minimalist real-time OSs, which are very popular in the industrial manufacturing of embedded systems, which we use daily to accomplish

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specific tasks. They are becoming more and more adopted to help define more generic, multiple-purpose development platforms. Low-end 8-bit microcontrollers In the past, 8-bit microcontrollers dominated the embedded market. The simplicity of their design allows us to write small applications that can accomplish a set of predefined tasks but are too simple and usually equipped with too few resources to implement an embedded system, especially since 32-bit microcontrollers have evolved to cover all the use cases for these devices within the same range of price, size, and power consumption. Nowadays, 8-bit microcontrollers are mostly relegated to the market of educational platform kits, aimed at introducing hobbyists and newcomers to the basics of software development on electronic devices. 8-bit platforms are not covered in this book because they lack the characteristics that allow advanced system programming, multithreading, and advanced features to be developed to build professional embedded systems. In the context of this book, the term embedded systems is used to indicate a class of systems running on microcontroller-based hardware architecture, offering constrained resources but allowing real-time systems to be built through features provided by the hardware architecture to implement system programming. Hardware architecture

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The architecture of an embedded system is centered around its microcontroller, also sometimes referred to as the microcontroller unit (MCU). This is typically a single integrated circuit containing the processor, RAM, flash memory, serial receivers and transmitters, and other core components. The market offers many different choices among architectures, vendors, price ranges, features, and integrated resources. These are typically designed to be inexpensive, low-resource, low-energy consuming, self- contained systems on a single integrated circuit, which is the reason why they are often referred to as System-on- Chip (SoC). Due to the variety of processors, memories, and interfaces that can be integrated, there is no actual reference architecture for microcontrollers. Nevertheless, some architectural elements are common across a wide range of models and brands, and even across different processor architectures. Some microcontrollers are dedicated to specific applications and expose a particular set of interfaces to communicate to peripherals and the outside world. Others are focused on providing solutions with reduced hardware costs, or with very limited energy consumption. Nevertheless, the following set of components is hardcoded into almost every microcontroller: Microprocessor RAM Flash memory Serial transceivers

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Additionally, more and more devices are capable of accessing a network, to communicate with other devices and gateways. Some microcontrollers may provide either well-established standards, such as Ethernet or Wi-Fi interfaces, or specific protocols specifically designed to meet the constraints of embedded systems, such as sub-GHz radio interfaces or a Controller Area Network (CAN) bus, being partially or fully implemented within the IC. All the components must share a bus line with the processor, which is responsible for coordinating the logic. The RAM, flash memory, and control registers of the transceivers are all mapped in the same physical address space:

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Embedded Systems Architecture - Second Edition (Daniele Lacamera) (z-library.sk, 1lib.sk, z-lib.sk)

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