1. OPERATING SYSTEM ( OS 023L1 ) EMBEDDED OPERATING SYSTEMS Presented By: GAGNO, Nelson Jr. MADAYAG, Maria Lourdes MAYBANTING, Jefferson RAMOS, Adrian Alvin SAN DIEGO, Eleonor Presented To: ENGR. ARIEL E. ISIDRO

2. What is anEmbedded Systems?

3. EMBEDDED SYSTEMS An embedded system is a combination of computer hardware and software, and perhaps additional mechanical or other parts, designed to perform a dedicated function.

5. Relaxed to very strict requirements and combinations of different quality requirements

7. Different application characteristics

9. Possible Organizationof an Embedded System

13. Protection is not necessary

15. Adapting an Existing Commercial Operating System An existing commercial OS can be used for an embedded system by adding real-time capability, streamlining operation, and adding necessary functionality.

16. Adapting an Existing Commercial Operating System An advantage of this approach is that the embedded OS derived from a commercial general-purpose OS is based on a set of familiar interfaces, which facilitates portability. The disadvantage of using a general-purpose OS is that it is not optimized for real-time and embedded applications.

17. Purpose-Built Embedded Operating System A significant number of operating systems have been designed from the ground up for embedded applications. Two prominent examples of this latter approach are eCos and TinyOS.

19. Scheduled policy is real time and dispatcher module is part of scheduler instead of separate component

21. Minimizes intervals during which interrupts are disabled

23. Provides bounded execution time for most primitives

25. Supports real-time queuing disciplines such as earliest deadline first and primitives for jamming a message into the front of a queue

27. WHAT IS AN eCos? eCos stands for Embedded Configurable Operating System It is an open source, royalty-free, real-time OS intended for embedded applications. It is one of the most widely used embedded operating systems.

28. CONFIGURABILITY An embedded system OS that is flexible enough to be used in a wide variety of embedded application and on a wide variety of embedded platforms must provide more functionality than will be needed for any particular application and platform.

29. CONFIGURABILITY The eCos configuration tool (which runs on Windows or Linux) is used to configure an eCos package to run on a target embedded system.

30. CONFIGURABILITY

31. LOADING ANeCos CONFIGURATION

32. eCos COMPONENTS A key design requirement for eCos is portability to different architectures and platforms with minimal effort.

33. eCos LAYERED STRUCTURE

34. HARDWAREABSTRACTION LAYER ( HAL ) The HAL is software that presents a consistent API to the upper layers and maps upper-layer operations onto a specific hardware platform. Thus, the HAL is different for each hardware platform.

36. Variant: Supports the features of the specific processor in the family.

38. Low task switching latency: The time it takes from when a thread becomes available to when actual execution begins.

39. Small memory footprint: Memory resources for both program and data are kept to a minimum by allowing all components to configure memory as needed.

41. Control over the various threads in the system

42. A choice of schedulers, determining which thread should currently be running

43. A range of synchronization primitives, allowing threads to interact and share data safely

45. eCos Principal Objective Efficiency No unnecessary software layering or irrelevant functionality. Device driver provide separate function for: Input Output Buffering Device control

46. eCos SCHEDULER Bitmaps Scheduler Efficient for small number of threads active. Each thread has different priority. Multilevel queue Scheduler Appropriate when number of threads is running. Multiple threads at each priority. Time slicing.

47. Terms to be remember… THREAD Client of the driver or simply a “process”. PRIORITY LEVEL Use by the scheduler to determine which thread ready to run. TIME SLICING Allow each thread at a given time to execute a given amount of time.

48. Terms to be remember… PREEMPTION Is a context switch halting execution of lower priority thread allowing higher priority thread to execute. SCHEDULER Selects appropriate thread for execution provide mechanisms for these executing threads to synchronize, and control the effect of interrupts on thread execution.

49. BITMAP SCHEDULER Allow the execution of threads at multiple priority levels; however, only single thread can exist at each priority level.

50. BITMAP SCHEDULER

51. MULTILEVEL QUEUE SCHEDULER Allow execution of multiple threads at each of it priority levels. Scheduler allows pre-emption and time slicing.

52. MULTILEVEL QUEUE SCHEDULER

53. eCosTHREAD SYNCHORNIZATION Thread synchronization requires that a running thread gain a "lock" on an object before it can access it. The thread will wait in line for another thread that is using the method/data member to be done with it. This is very important to prevent the corruption of program data if multiple threads will be accessing the same data. If two threads try to change a variable or execute the same method at the same, this can cause serious and difficult to find problems. Thread synchronization helps prevent this.

54. eCosTHREAD SYNCHORNIZATION Classics Mechanism Mutexes Semaphores Condition variables Synchronization/ Communication Mechanism Event flags Mailboxes SMP support (symmetric/ multiprocessing) Spinlocks

55. Mutual Exclusion Lock( MUTEXES ) A mutex is used to enforce mutually exclusive access to a resource, allowing only one thread at a time to gain access. The mutex has only two states: locked and unlocked.

56. Lock and Unlocked When a mutex is locked by one thread, any other thread attempting to lock the mutex is blocked. When the mutex is unlocked, then one of the threads blocked on this mutex is unblocked and allowed to lock the mutex and gain access to the resource.

57. SEMAPHORES A counting semaphore is an integer value used for signaling among threads. Counting semaphores are suited to enabling threads to wait until an event has occurred. Useful for resource management.

58. SEMAPHORES If this counter is zero, an attempt by a consumer thread to wait on the semaphore will block until some other thread or a DSR posts a new event to the semaphore. If the counter is greater than zero then an attempt to wait on the semaphore will consume one event; in other words, decrement the counter, and return immediately.

59. CONDITIONAL VARIABLES A condition variable is used to block a thread until a particular condition is true. Condition variables are used with mutexes to allow multiple thread to access shared data.

60. EVENT FLAGS An event flag is a 32-bit word used as a synchronization mechanism. Application code may associate a different event with each bit in a flag. A thread can wait for either a single event or a combination of events by checking one or multiple bits in the corresponding flag.

61. MAILBOXES It is also called message boxes, are an eCos synchronization mechanism that provides a means for two threads to exchange information. The eCos mailbox mechanism can be configured for blocking or nonblocking on both the send and receive side.

62. SPINLOCKS A spinlock is a flag that a thread can check before executing a particular piece of code. Basically, only 1 thread at a time can acquire a spinlock. Any other thread attempting to acquire the same lock will keep trying (spinning) until it can acquire a lock.

63. Tinyos

64. WHAT IS A TINYOS? TinyOS is a free and open source component-based operating system and platform targeting wireless sensor networks. TinyOS is an embedded operating system written in the nesC programming language as a set of cooperating tasks and processes.

65. WIRELESS SENSOR NETWORKS TINYOS was developed primarily for use with networks of small wireless sensor. A number of trends have enabled the development of extremely compact, low-power sensors. The well-known Moore’s law continuous to drive down the size of memory and processing logic elements. Smaller size in turn reduces power consumption. Low power and small size treads are also evident in wireless communication hardware, micro-electrical sensors (MEMS) and transducers.

66. NETWORK TOPOLOGY

71. TASK Within a component, tasks are atomic: Once a task has started, it runs to completion. It cannot be preempted by another task in the same component, and there is no timeslicing. However, a task can be preempted by an event. A task cannot block or spin wait.

72. COMMAND It is a nonblocking requests. A command is typically a request for the lower-level component to perform some service, such as initiating a sensor reading.

73. EVENTS In TinyOS may be tied either directly or indirectly to hardware events. The lowest level software components interface directly to hardware interrupts, which may be external interrupts, timer events, or counter events. An event handler in a lowest level component may handle the interrupt itself or may propagate event messages up through the component hierarchy.

74. TINYOS RESOURCE INTERFACE The TINYOS scheduler operates across all components. Virtually all embedded systems using TINYOS will be uni-processor systems, so that only one task among all the tasks in all the components may execute at a time. The scheduler is a separate component. It is the only portion of TINYOS that must be present in any system.

79. SHARED RESOURCE CONFIGURATION

80. Thank you!!