Embedded Operating Systems lecture notes
- 2. Embedded System – The use of electronics and software within a product that has a specific function or set of functions, as opposed to a general-purpose computer – smartphones, digital cameras, video cameras, calculators, home security systems, household appliances… – …various automotive systems, and numerous types of sensors and actuators in automated systems Giorgio Giacinto 2019 Operating Systems 2
- 3. Embedded System Embedded systems are often tightly coupled to their environment Real-time constraints imposed by the need to interact with the environment Constraints on speed, measurements, time durations, and the like, dictate the timing of software operations If multiple activities must be managed simultaneously, this imposes more complex real-time constraints Giorgio Giacinto 2019 Operating Systems 3
- 4. Application Processors vs Dedicated Processors – Application Processor – General Purpose with ability to execute complex operating systems, such as Linux, Android, and Chrome – Dedicated Processor – Specialized to perform one or a small number of specific tasks – The processor and associated components can be engineered to reduce size and cost – An Embedded System is comprised by several dedicated processors and, optionally, one or more application processors Giorgio Giacinto 2019 Operating Systems 4
- 5. Automotive Systems Giorgio Giacinto 2019 Operating Systems 5
- 6. Organization of an embedded system Memory Custom logic Human interface Diagnostic port Processor D/A Conversion Actuators/ indicators A/D conversion Sensors Giorgio Giacinto 2019 Operating Systems 6
- 7. Typical microcontroller chip Figure 13.3 Typical Microcontroller Chip Elements A/D converter Analog data acquisition Temporary data Processor System bus RAM D/A converter ROM Serial I/O ports EEPROM Parallel I/O ports TIMER Program and data Permanent data Timing functions Analog data transmission Send/receive data Peripheral interfaces Giorgio Giacinto 2019 Operating Systems 7
- 8. Deeply Embedded System – Relies on a microcontroller rather than on a microprocessor – It is not programmable once the program logic for the device has been burned into ROM – No interaction with a user – Dedicated, single-purpose devices that detect something in the environment, perform a basic level of processing, then do something with the results – Extreme resource constraints in terms of memory, processor size, time, and power consumption – The Internet ofThings depends heavily on deeply embedded systems – Often wireless capability Giorgio Giacinto 2019 Operating Systems 8
- 9. Characteristics of Embedded OS Real-time operation Reactive operation Configurability I/O device flexibility Streamlined protection mechanisms Direct use of interrupts Giorgio Giacinto 2019 Operating Systems 9
- 10. Developing an EmbeddedOS Two general approaches • Take an existing OS and adapt it for the embedded application • Design and implement an OS intended solely for embedded use Giorgio Giacinto 2019 Operating Systems 10
- 11. Adapting an existingOS Giorgio Giacinto 2019 Operating Systems 11
- 12. Adapting an ExistingOS – An existing commercial OS can be used for an embedded system by adding – Real time capability – Streamlining operation – Adding necessary functionality Advantage • Familiar interface Disadvantage • Not optimized for real-time and embedded applications Giorgio Giacinto 2019 Operating Systems 12
- 13. Cross Platform Development – Typically, the development of an operating system is carried out on the same hardware platform it is built for. – In the case of embedded system, development is carried out on a platform that is different from the target systems Host •Cross-platform development environment •Kernel •Root file system •Boot loader Target Giorgio Giacinto 2019 Operating Systems 13
- 14. Kernel Compilation Figure 13.5 Kernel Compilation Cross Compiler Kernel image Kernel Configuration Defined according to target hardware and system requirements From open source or hardware vendor Executable on host system Executable on target system; ready to be started by boot loader on target system Kernel Source Giorgio Giacinto 2019 Operating Systems 14
- 15. Embedded Linux – An embedded Linux distribution is customized for the size and hardware constraints of embedded devices – Includes software packages that support a variety of services and applications on those devices – An embedded Linux kernel will be far smaller than an ordinary Linux kernel – Example: Giorgio Giacinto 2019 Operating Systems 15
- 16. Size of Linux Kernel Figure 13.6 Size of Linux Kernel (shown in GZIP-compressed file size) 1992 15 30 45 60 75 90 106 120 135 1994 1996 megabytes 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 GZIP-compressed file size Giorgio Giacinto 2019 Operating Systems 16
- 17. Embedded Linux File Systems – File system must be as small as possible. – cramfs – A simple read-only file system that is designed to minimize size by maximizing the efficient use of underlying storage – Files are compressed in units that match the Linux page size – squashfs – A compressed, read-only file system that was designed for use on low memory or limited storage size environments – jffs2 – A log-based file system that is designed for use on NOR and NAND flash devices with special attention to flash-oriented issues such as wear-leveling – ubifs – Provides better performance on larger flash devices and also supports write caching to provide additional performance improvements – yaffs2 – Provides a fast and robust file system for large flash devices Giorgio Giacinto 2019 Operating Systems 17
- 18. Advantages of Embedded Linux – Vendor independence – Varied hardware support – Linux support for a wide range of processor architectures and peripheral devices – Low cost for development and training – The use of Linux provides all of the advantages of open source software Giorgio Giacinto 2019 Operating Systems 18
- 19. 𝜇Clinux 𝜇Clinux (microcontroller Linux) is an open-source Linux kernel variation targeted at microcontrollers and other very small embedded systems The design philosophy for 𝜇Clinux is to slim down the operating environment by removing utility programs, tools, and other system services that are not needed in an embedded environment Giorgio Giacinto 2019 Operating Systems 19
- 20. Differences Between 𝜇Clinux and Linux – Linux is a multiuser OS based on Unix. 𝜇Clinux is intended for embedded systems typically with no interactive user – 𝜇Clinux does not support memory management – The Linux kernel maintains a separate virtual address space for each process. 𝜇Clinux has a single shared address space for all processes – 𝜇Clinux only provides the vfork() system call for process creation Giorgio Giacinto 2019 Operating Systems 20
- 21. Designing a specificOS Giorgio Giacinto 2019 Operating Systems 21
- 22. Purpose-Built EmbeddedOS – Fast and lightweight process or thread switch – Scheduling policy is real time and dispatcher module is part of scheduler – Small size – Responds to external interrupts quickly – minimizes intervals during which interrupts are disabled – Provides fixed or variable-sized partitions for memory management – Provides special sequential files that can accumulate data at a fast rate Examples of ad-hoc embedded OS • eCos • TinyOS Giorgio Giacinto 2019 Operating Systems 22
- 23. Timing Constraints The kernel • Provides bounded execution time for primitives • Maintains a real-time clock • Provides for special alarms and timeouts • Supports real-time queuing disciplines • Provides primitives to delay processing by a fixed amount of time and to suspend/resume execution Giorgio Giacinto 2019 Operating Systems 23
- 24. TinyOS https://github.com/tinyos/tinyos-main – Streamlines to a very minimal OS for embedded systems – Core OS requires 400 bytes of code and data memory combined – Has become a popular approach to implementing wireless sensor network software – Not a real-time OS – There is no kernel – There are no processes – OS doesn’t have a memory allocation system – Interrupt and exception handling is dependent on the peripheral – It is completely nonblocking, so there are few explicit synchronization primitives Giorgio Giacinto 2019 Operating Systems 24
- 25. TinyOS Components – Embedded software systems built withTinyOS consist of a set of modules (called components), each of which performs a simple task and which interface with each other and with hardware in limited and well-defined ways – The only other software module is the scheduler – Because there is no kernel there is no actual OS Examples of standardized components include: • Single-hop networking • Ad-hoc routing • Power management • Timers • Nonvolatile storage control Giorgio Giacinto 2019 Operating Systems 25
- 26. Components andTasks – A software component implements one or more tasks – Each task in a component is similar to a thread in an ordinary OS – Within a component tasks are atomic – Once a task has started it runs to completion A task cannot • Be preempted by another task in the same component and there is no time slicing • Block or spin wait A task can • Perform computations • Call lower-level components (commands) • Signal higher-level events • Schedule other tasks Giorgio Giacinto 2019 Operating Systems 26
- 27. TinyOS Scheduler – Operates across all components – Only one task executes at a time – The scheduler is a separate component that must be present in any system – Default scheduler is a simple FIFO queue – Scheduler is power aware – Puts processor to sleep when there is no task in the queue Giorgio Giacinto 2019 Operating Systems 27
- 28. Blackberry QNX – QNX – QNX Neutrino RTOS Realtime embedded system, microkernel design, and modular architecture that supports hundreds of POSIX commands, utilities, and programming interfaces – QNX OS for Automotive Safety – QNX OS for Medical – Wide adoption in the automotive sector Giorgio Giacinto 2019 Operating Systems 28
- 29. QNX Neutrino System Architecture Giorgio Giacinto 2019 Operating Systems 29
- 30. QNX Neutrino microkernel – thread services (POSIX thread-creation) – signal services (POSIX signal) – message-passing services – the microkernel manages the exchange of messages between threads synchronization services (POSIX thread- synchronization) – scheduling services (POSIX realtime scheduling policies) – timer services (POSIX timer services) – process management services Giorgio Giacinto 2019 Operating Systems 30
- 31. VxWorks and Integrity – Wind River – VxWORKS RTOS with different profiles for different application scenarios. This OS equipped the MARS Curiosity mission (NASA) – Green Hills – Integrity RTOS with a separation kernel for different markets Giorgio Giacinto 2019 Operating Systems 31
- 32. LYNX – LYNX – LYNXOS RTOS LynxOS® is a deterministic, hard real-time operating system that provides POSIX-conformant APIs in a small- footprint embedded kernel. LynxOS provides symmetric multi-processing support to fully take advantage of multi- core/multi-threaded processors Giorgio Giacinto 2019 Operating Systems 32