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§2.1 The Programmers Abstract Machine Douglas Wilhelm Harder, M.Math. LEL Department of Electrical and Computer Engineering University of Waterloo Waterloo,

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Presentation on theme: "§2.1 The Programmers Abstract Machine Douglas Wilhelm Harder, M.Math. LEL Department of Electrical and Computer Engineering University of Waterloo Waterloo,"— Presentation transcript:

1 §2.1 The Programmers Abstract Machine Douglas Wilhelm Harder, M.Math. LEL Department of Electrical and Computer Engineering University of Waterloo Waterloo, Ontario, Canada © 2012 by Douglas Wilhelm Harder. Some rights reserved. Based in part on Gary Nutt, Operating Systems, 3 rd ed.

2 Chapter 2: Using the Operating System Topics: –The programmers abstract machine –Resources –Processes and threads –Writing concurrent programs –Objects 2

3 Outline This topic introduces the abstract machine –Abstract and virtual machines –Cloud computing –Computing resources over time Consequences –Sequential and parallel computation Examples: quick sort and merge sort –Implementation The Programmer's Abstract Machine 3

4 Abstract Machines The operating system provides an abstract interface between the programmer and the hardware –Suppose you had to rewrite an application as large as a word processor each time a company built a new CPU An operating system reduces development costs but increases run times with respect to any interactions –The use of main memory and the CPU is invisible to the programmer –The interaction between the programmer and devices is through function calls in libraries –Programs must still be complied and translated into machine instructions and linked to the various libraries The Programmer's Abstract Machine 4

5 Virtual Machines One recent further abstraction is to the creation of virtual machines –Now the individual machine instructions become abstracted to a common set of instructions –Programs written in Java and C#, for example, need only be compiled once after which they can be run on any machine that implements a virtual machine The Java Virtual Machine (JVM) runs Java byte code The Common Language Runtime (CLR) of the.NET framework runs an Intermediate Language –Again, the benefits are reduced development costs and further increased run times The Programmer's Abstract Machine 5

6 Cloud Computing Even more recent is the advent of cloud computing –Now even the individual machines are abstracted away –Computing becomes a service which is seamlessly distributed to available resourcesincluding the possibility of multiple remote processors As always, the benefits are reduced development costs and further increased run times The Programmer's Abstract Machine 6

7 Computing Resources Moores law allows us to afford the additional costs The Programmer's Abstract Machine User: Wgsimon 7

8 Computing Resources Other resources are also increasing exponentially: –Hard drive capacity is following a similar curve to Moores law Kyders law –Butters law makes similar predictions about network capacity –Nielsen's law says bandwidth doubles each year –Headys law observes that pixels-per-dollar also follows Moores law Caveat: –Moores Second Law says that the capital costs for semiconductor fabrication also increases exponentially... The Programmer's Abstract Machine 8

9 Hint for Fame An engineers recipe for fame (if not fortune): 1.Find an exponentially increasing process 2.Call it a law 3.Publicize it 4.Get it named after you... The Programmer's Abstract Machine 9

10 Computing Resources Not all resources improve so quickly: –Seek time has only halved from 20 ms in 1990 to 9 ms today Down to 3 ms for high-end server drives –Transfer rates depend on rotational speed The 7200 rpm Barracuda was introduced in rpm hard drives became available in –300 MB/s transfer rates –Cost: 5¢/GB – 10¢/GB Solid state drives improve on this –Transfer rates of 100–500 MB/s –Cost: $1/GB – $2/GB The Programmer's Abstract Machine 10

11 Computing Resources Clock speed used to follow Moores law –It doubled every two years –It reached a plateau in 2002 at 3 GHz –The best available today is 4 GHz There are other solutions –Using multiple processors –Multi-core processors –Distributed computing The Programmer's Abstract Machine Multiple serial processing elements (SPEs) 11

12 Computing Resources There were concerns over a memory wall in the 1990s: –CPU speed was following Moores law –The speed of RAM increased more slowly: 10 % per annum –Memory was becoming the bottleneck With the CPU clock rates plateau, RAM has caught up: –DDR SDRAM started at 100 MHz –DDR4 SDRAM capable of 4 GHz There are other solutions –More registers in the processor –Multiple levels of caching on the processor On multi-core machines, each core may have a L1 cache while the cores may share L2 and L3 caches The Programmer's Abstract Machine 12

13 Consequences Despite the additional levels of abstraction being placed on top of the hardware, hardware improvements more than make up for this additional cost To benefit from multiple serial processing elements, we first need to look at our execution model The Programmer's Abstract Machine 13

14 Computation There are two techniques for execution: –Sequential execution –Parallel sequential execution The Programmer's Abstract Machine 14

15 Sequential Computation In a sequential execution, programs follows a predictable sequence of instructions –Branching and jumps are defined by conditional and looping statements as well as function calls Given a problem: –An algorithm is designed to solve that problem –It is implemented in a high-level programming language: source –It is compiled into machine instructions: binary program –The binary program is executed It requests and frees resources and determines the solution The Programmer's Abstract Machine 15

16 Sequential Computation In a sequential execution, the sub-problems are solved through function calls –Functions have a well defined entrance and exit points –The calling function halts execution until the function returns The Programmer's Abstract Machine 16

17 Parallel Sequential Computation As an alternative, consider the following modification: –Break the base problem into independent tasks –For each task, determine an algorithm that solves it –Implement the solutions as source code There is one base task –Compile the solutions into a binary program –When executed, the binary program begins a sequential execution of the base task If another task must be executed, it begins execution as a sequential computation parallel to the base task The Programmer's Abstract Machine 17

18 Parallel Sequential Computation There is a hierarchical relationship between tasks –There is one base task –Each other task is forked as the parallel execution of another executing task –This creates a tree structure –We will refer to parent tasks and child tasks The Programmer's Abstract Machine 18

19 Parallel Sequential Computation In a parallel execution, the tasks are forked from another tasks, however, the original continues executing –Child tasks have well defined entrance points relative to the parent task –The parent task continues execution This can happen when: –The parent does not require an immediate result from the child –It does not matter in which order the parent or child are executed The Programmer's Abstract Machine 19

20 Example: Quick Sort Consider quick sort: –Select a pivot point in the list –Distribute the entries relative to the pivot –Recursively call quick sort on each of the two sub-lists When quick sort returns, that sub-list is sorted –We only have to know when all recursive tasks are complete Each recursive call could occur in parallel –If so, the run-time can be reduced from (n ln(n)) to (n) The Programmer's Abstract Machine 20

21 Example: Merge Sort Consider merge sort: –Divide the list into two –Recursively sort each of the sub-lists –Merge the results Problem: –We can apply merge sort on each sub-list in parallel –The parent task, however, must know when the two child tasks are complete before the sorted sub-lists can be merged The Programmer's Abstract Machine 21

22 How are Tasks Implemented? How are the parent and child tasks related? –Is the memory shared or distributed? –Is the data shared or distributed? There are numerous models: –The thread model has the executing tasks share memory and resources –The message passing model has each task executing as an independent process with an inter-process message passing interface –The data parallel model has each task accessing the same memory, but memory is partitioned between the tasks The Programmer's Abstract Machine 22

23 The CMSIS Interface ARM Holdings, as well as specifying –The ARMv7 architecture –The Cortex-M3 microcontroller interface also specifies an interface to an RTOS: CMSIS –Any application using this interface can be compiled to a platform which implements this interface –All images and interfaces based on 23 The Programmer's Abstract Machine

24 CMSIS The Cortex TM Microcontrol Software Interface Standard (CMSIS) is an interface to the underlying microcontroller 24 The Programmer's Abstract Machine

25 CMSIS The user can access the hardware either through the interface or through direct calls 25 The Programmer's Abstract Machine

26 CMSIS CMSIS specifies data structures, defines, typedefs, enumerations and functions –You can download the specifications from the ARM website: cortex-microcontroller-software-interface-standard.php 26 The Programmer's Abstract Machine

27 CMSIS RTOS functions defined in CMSIS include: –Kernel status –Thread management –Waiting on events –Timer management –Sending and receiving signals –Mutual exclusion and semaphores for concurrency –Memory pool management –Message handling –Mail queue management 27 The Programmer's Abstract Machine

28 CMSIS Kernel status: –Start the kernel and check its status osStatus osKernelStart ( osThreadDef_t *thread_def, void *argument ) int32_t osKernelRunning ( void ) 28 The Programmer's Abstract Machine

29 CMSIS Thread management: –Create or terminate a thread, get or set a threads priority, and accessing this threads ID or forcing it to yield the processor osThreadId osThreadCreate ( osThreadDef_t *thread_def, void *argument) osStatusosThreadTerminate ( osThreadId thread_id ) osStatus osThreadSetPriority ( osThreadId thread_id, osPriority priority ) osPriority osThreadGetPriority ( osThreadId thread_id ) osThreadId osThreadGetId ( void ) osStatusosThreadYield ( void ) 29 The Programmer's Abstract Machine

30 CMSIS Timer management: –Create, start or restart, and stop a timer osTimerId osTimerCreate ( osTimerDef_t *timer_def, os_timer_type type, void *argument ) osStatus osTimerStart ( osTimerId timer_id, uint32_t millisec ) osStatus osTimerStop ( osTimerId timer_id ) 30 The Programmer's Abstract Machine

31 CMSIS Waiting on events: –Wait for a time delay or wait for any event (signal, message, mail, or time delay) osStatus osDelay ( uint32_t millisec ) osEvent osWait ( uint32_t millisec ) 31 The Programmer's Abstract Machine

32 CMSIS Sending and receiving signals: –Set, get, clear, or wait on a signal of an executing thread int32_t osSignalSet ( osThreadId thread_id, int32_t signal ) int32_t osSignalGet ( osThreadId thread_id ) int32_t osSignalClear ( osThreadId thread_id, int32_t signal ) osEvent osSignalWait ( int32_t signals, uint32_t millisec ) 32 The Programmer's Abstract Machine

33 CMSIS Mutual exclusion and semaphores for concurrency: –Create and initialize, wait on, and release a mutual exclusion flag osMutexId osMutexCreate ( osMutexDef_t *mutex_def ) osStatus osMutexWait ( osMutexId mutex_id, uint32_t millisec ) osStatus osMutexRelease ( osMutexId mutex_id ) –Create and initialize, wait on, and release a semaphore osSemaphoreId osSemaphoreCreate ( osSemaphoreDef_t *semaphore_def, int32_t count ) int32_t osSemaphoreWait ( osSemaphoreId semaphore_id, uint32_t millisec ) osStatus osSemaphoreRelease ( osSemaphoreId semaphore_id ) 33 The Programmer's Abstract Machine

34 CMSIS Memory pool management: –Create and initialize, allocate (possibly zeroing), and free memory within a pool osPoolId osPoolCreate ( osPoolDef_t *pool_def ) void * osPoolAlloc ( osPoolId pool_id ) void * osPoolCAlloc ( osPoolId pool_id ) osStatus osPoolFree ( osPoolId pool_id, void *block ) 34 The Programmer's Abstract Machine

35 CMSIS Message handling: –Creating, sending, and waiting on a message osMessageQId osMessageCreate ( osMessageQDef_t *queue_def, osThreadId thread_id ) osStatus osMessagePut ( osMessageQId queue_id, uint32_t info, uint32_t millisec ) osEvent osMessageGet ( osMessageQId queue_id, uint32_t millisec ) 35 The Programmer's Abstract Machine

36 CMSIS Mail and mail queue management: –Create and initialize a mail queue and allocate memory for (possibly zeroing), send, receive, and free memory for mail osMailQId osMailCreate ( osMailQDef_t *queue_def, osThreadId thread_id ) void * osMailAlloc ( osMailQId queue_id, uint32_t millisec ) void * osMailCAlloc ( osMailQId queue_id, uint32_t millisec ) osStatus osMailPut ( osMailQId queue_id, void *mail ) osEvent osMailGet ( osMailQId queue_id, uint32_t millisec ) osStatus osMailFree ( osMailQId queue_id, void *mail ) 36 The Programmer's Abstract Machine

37 CMSIS CMSIS is an interface for a real-time operating system –Any vendor could implement additional functions –An interface that implements all CMSIS-defined algorithms is said to be CMSIS compliant 37 The Programmer's Abstract Machine

38 Summary This topic covered the abstract machine –Abstract and virtual machines –Cloud computing –Computing resources over time Consequences –Sequential and parallel computation Examples: quick sort and merge sort –Implementation details of CMSIS The Programmer's Abstract Machine 38

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