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The Simple Scheduler in Embedded System @ OSDC.TW 2014
The document describes a simple scheduler module implemented in C for embedded systems. It breaks processes into small jobs represented by functions that are scheduled in a first-in, first-out queue without preemption. This allows embedding an operating system concept into simple systems using only functions and a ready queue. Interrupts can add jobs to the queue. The scheduler and example oscilloscope application demonstrate scheduling without process state using only callbacks.
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Similar to The Simple Scheduler in Embedded System @ OSDC.TW 2014
The Simple Scheduler in Embedded System @ OSDC.TW 2014
- 1. The Simple Schedulerin Embedded System A simple scheduler module implemented in C StarNight @ OSDC.TW 2014
- 2. Who am I? 潘建宏/ Jian-Hong Pan (StarNight) About Me : http://about.me/StarNight 出沒在～ GitHub : starnight PTT : zack2004 plurk : StarNight Facebook : Jian-Hong Pan 目前繼續在種花店當個打雜園丁 ～
- 3. Outline ● History ● OSconcepts learned from textbooks ● Process & Scheduler ● What if … ● Simple Scheduler ● Simple Oscilloscope
- 4. 很久很久以前～ Long Long timeago ~ 很久很久以前～ Long Long time ago ~
- 5. There is arobot in every boy’s mind ~ 每個男孩心中， 都有一個機器人～
- 6. There is anoperating system in every computer scientist’s mind ~ 上了大學之後， 同學告訴我每位資工人的 心中都有個 OS OS ~
- 7. However, I amgraduated from department of mechanical engineering ~ 但我是機械系畢業的~
- 8. For the expectationin my childhood, not only I attended the required classes, but also I sat in the operating system class ~ 為了男孩心中的機器人 所以除了本科外，我旁聽 ~
- 9.
- 10.
- 11. My First Impressionof OS Operating System Input Output keyboard mouse microphone touchpad comunication (in) ... screen headset comunication (out) ...
- 12. There could bean OS in a robot, too! Operating System Input Output GPI sensors command (in) comunication (in) ... GPO motors command (out) comunication (out) ...
- 13. Thinking furthermore Apps Operating System Input Output driversscheduler etc ... ETC ready queue data structure Simple Data Structure @ lightning talk COSCUP 2013
- 14. Data Text Heap Stack max base 0 Process inMemory Temporary data Dynamic allocated memory Global variables Program code Reference: Figure 3.1 of Operating System Concept, 8th
- 15. Usual Diagram ofProcess State new ready terminated running Waiting admitted exit interrupt scheduler dispatch I/O or event wait I/O or event completion Reference: Figure 3.2 of Operating System Concept, 8th
- 16. Process Control Block(PCB) Process State Process Number Program Counter Registers Memory Limits List of Open Files Reference: Figure 3.3 of Operating System Concept, 8th
- 17. Scheduling when 4Events Occurs new ready terminated running Waiting admitted exit interrupt scheduler dispatch I/O or event wait I/O or event completion Reference: Figure 3.2 of Operating System Concept, 8th 1 2 34 For Multitasking For Multiprogramming
- 18. Scheduling Algorithms ● First-Come,First-Served (or FIFO) ● Round Robin ● Shortest Job First ● Shortest Remaining Time First ● Priority Scheduling ● Multilevel Queues
- 19. What if ... ●The scheduled job (process) is as small & simple as a function, even is a function. ● Because of being small, the job will not be interrupted by timeout. ● Because of being simple, the job will not wait for the I/O or event. There is another job for I/O or event completion.
- 20. Running Waiting Ready Before I/Oor event During I/O or event After I/O or event Compare Jobs’ Status Changing Job #1 Job #2 Job #3 General Simple Scheduler Time ToDoAsync DoAsync AfterAsync
- 21. In other words ●Break a single process into several jobs. ● Each job will not be interrupted. ● A job terminate immediately if it is finished. ● Do not save job’s state during context switching.
- 22. This is notnew idea Related concepts: ● Functional programming ● Asynchronous function in Javascript ● Events of GUI programs ● Function pointer in C ToDoAsyncFunc(pArgument, pAfterFunc)
- 23. How do itkeep the jobs until they are executed? Save the jobs in somewhere, maybe a queue. How about make it like the ready queue of scheduler !?!?
- 24. What is SimpleScheduler ● Simple Scheduler does "First In, First Out" (FIFO) scheduling works with no priority and non-preemptive scheduling scheme. ● It is the "Functions", which could also be called callback functions or jobs, that Simple Scheduler schedules.
- 25. You can haveit from GitHub → StarNight → simple scheduler https://github.com/starnight/simple-scheduler PS. Wiki included
- 26. Job’s State inSimple Scheduler new ready terminated running admitted exit scheduler dispatch Ready Queue interrupt scheduler dispatch Waiting I/O or event wait I/O or event completion Small & non-preemptive Simple & non-blocking I/O
- 27. Job’s State inSimple Scheduler new ready terminated running scheduler dispatch Ready Queue admitted exit Do scheduling
- 28. Timing Diagram Job #1Job #2 Ready Queue: First In, First Out (FIFO)
- 29. Timing Diagram Job #1Job #2 Ready Queue: Job #1
- 30. Timing Diagram Job #1Job #2 Ready Queue: Job #1 admits one Job #2Job #2 Job #2
- 31. Timing Diagram Job #2Job #2 Ready Queue:
- 32. Timing Diagram Job #2Job #2 Ready Queue: Job #2
- 33.
- 34. Timing Diagram Job #2 ReadyQueue: An interrupt occurs during scheduling
- 35. Timing Diagram Job #2 ReadyQueue: The interrupt admits one Job #3 Job #3 Job #3
- 36. Timing Diagram Job #2 ReadyQueue: Job #3
- 37. Timing Diagram Job #2Job #3 Ready Queue: Job #2
- 38. Timing Diagram Job #2 ReadyQueue: Job #3 Another interrupt occurs during Job #2 executing
- 39. Timing Diagram Job #2 ReadyQueue: Job #3 The interrupt admits one Job #1 Job #1 Job #1
- 40. Timing Diagram Job #2Job #1 Ready Queue: Job #3
- 41. Timing Diagram Job #3 ReadyQueue: Job #1
- 42. Timing Diagram Job #1 ReadyQueue: Job #3 Job #3
- 43.
- 44. Timing Diagram Ready Queue: Job#1 Job #1
- 45. Timing Diagram Job #1 ReadyQueue: Job #1 admits one Job #2 Job #2 Job #2
- 46.
- 47. Timing Diagram Job #2 ReadyQueue: Job #2
- 48.
- 49.
- 50. When does itadmit job? ● Booting (Before scheduler start to run) ● A Job is running ● During interrupt
- 51. 哥schedule的不是Process, 是Function It isthe functions, not the processes, that simple scheduler schedules.
- 52. typedef void (*SS_CB)(void*); ● The job could be pass one parameter's pointer or NULL representing no parameter. ● The pointer of the parameter could be a native variable pointer or even a struture pointer. Prototype of the Scheduled Function
- 53. /* Packaged callbackfunction (PCB). */ typedef struct _SS_PACKAGED_CALLBACK { SS_CB cb; void *p; } SS_PCB; PCB Structure Type ● cb : The callback function pointer of the job. ● p : The argument pointer going to be passed into the job. Ready Queue PCB of Job #3 PCB of Job #2 PCB of Job #1 FI FO
- 54. PCB vs PCB ProcessState Process Number Program Counter Registers Memory Limits List of Open Files SS_CB cb Callback function pointer void *p Parameter pointer for the callback function Original PCB Simple Scheduler PCB
- 55. Public Functions ● SSInit: Initial the scheduler. ● SSAdmitJob : Admit a job (callback function) into the ready queue. ● SSMainLoop : Main loop for system scheduling. ● SSBreak : Break scheduling. ● SSConsumeLeft : Consume left jobs in ready queue. ● SSDebug : Have the debug information of the scheduler.
- 56. SSBreak(BC) SSBreak(B) Scheduler’s State inSimple Scheduler Boot Run Break & Consume Left SSConsumeLeft(n) or SSBreak(BC) SSBreak(B) Break B: SS_BREAKSCHEDULING BC: SS_BREAKANDCONSUMELEFT SSMainLoop()
- 57.
- 58. ADC & UART& Timer Labs + Scheduler 實作一個窮到只剩下 $$ Scheduler的OS kernel Simple OS for Simple Oscilloscope https://github.com/starnight/Simple-Oscilloscope
- 59. 樸實無華 X 極簡 Assimple as possible ~
- 60. Architecture Scheduler Direvers Timer App #1App #N Kernel User
- 61. Fill Modules intoArchitecture Simple Scheduler ADC USART SysTimer ADCSample Process Kernel User Timer USARTCommunicate MODBUS - like Platform Dependent Drivers
- 62. Usage of SimpleScheduler ● SSInit() ● Admit leading jobs, ex: Wait command job. ● SSMainLoop() ● Interrupts admit jobs ○ USART RX: ■ Admits a job when predefined RX queue is full. ○ USART TX: ■ Admits a job when predefined TX queue is empty.
- 63. Usage of SimpleScheduler (Cont.) ● Jobs admit jobs (Ex: Modbus-like package) ○ Wait Commad: ■ Admits a wait command job if there is no command. ■ Admits a check station job if there is a command. ○ Check station job: ■ Admits a wait command job if not matched address. ■ Parses commad and admits a corresponding job. ○ Corresponding job: ■ ...
- 64. Simple Oscilloscpe -MCU Side
- 65. Simple Oscilloscpe -Wave Gen. Side
- 66.
- 67. Oscilloscope Console bypython + pyserial + matplotlib
- 68.
- 69. ● MVMC &ACAL Labs @ NCU ○ 老師們與歷屆學長、同學和學弟們 ● 作業系統Operating Systems on Share Course ● 我旁聽的作業系統課 @ NCU ● Textbook: Operating System Concepts ● Open Source Groups Thanks to
- 70. Thank you ~ andQ & A GitHub → starnight → simple-scheduler
- 71. Between Running andReady State ready running interrupt scheduler dispatch Ready * NRunning Running Job’s state according to time: Time Interrupted by timeout For Multitasking
- 72. The Waiting State Waiting I/O event waitI/O event completion WaitingRunningReady Job’s state according to time: Time For Multiprogramming
- 73. Diagram showing CPUswitch from process to process Reference: Figure 3.4 of Operating System Concept, 8th
- 74. ● SS_READYQUEUEOK ○ Theready queue works fine. ● SS_READYQUEUEEMPTY ○ The ready queue is empty. ● SS_READYQUEUEFULL ○ The ready queue is full. Ready Queue Status Ready Queue PCB of Job #3 PCB of Job #2 PCB of Job #1 FI FO
- 75. Job’s State inSimple Scheduler new ready terminated running admitted exit scheduler dispatch Ready Queue SSAdmitJob SSMainLoop
- 76. Scheduler Status ● SS_RUNSCHEDULING ○The scheduler is running. ● SS_BREAKSCHEDULING ○ The scheduler is or is going to be broken into stop. ● SS_BREAKANDCONSUMELEFT ○ The scheduler is or is going to be broken into stop and consume the left jobs in ready queue. Represented by SS_SSTATUS → run
- 77. Recall thinking furthermore Apps Operating System InputOutput drivers scheduler etc ... ETC ready queue data structure