Introduction to Real-Time Systems ECE 397-1

Transcription

1 Introduction to Real-Time Systems ECE Northwestern University Department of Computer Science Department of Electrical and Computer Engineering Teachers: Robert Dick Peter Dinda Office: L477 Tech 338, 1890 Maple Ave. Phone: Webpage: 1

2 Homework index 1 Lab six

3 Goals for lecture Lab four? Lab six Simulation of real-time operating systems Impact of modern architectural features 3

4 Lab four Please or hand in the write-up for lab assignment four Problems? See me. Will need everything from lab four working for lab six 4

5 Lab six Develop priority-based cooperative scheduler for TinyOS that keeps track of the percentage of idle time. Develop a tree routing algorithm for the sensor network. Send noise, light, and temperature data to a PPC, via the network root. Have motes respond to send audio samples and buzz commands. Play back or display this data on PPCs to verify the that the system functions. 5

6 Outline Introduction Role of real-time OS in embedded system Related work and contributions Examples of energy optimization Simulation infrastructure Results Conclusions 6

7 Introduction Real-Time Operating Systems are often used in embedded systems. They simplify use of hardware, ease management of multiple tasks, and adhere to real-time constraints. Power is important in many embedded systems with RTOSs. RTOSs can consume significant amount of power. They are re-used in many embedded systems. They impact power consumed by application software. RTOS power effects influence system-level design. 7

8 Introduction Real Time Operating Systems important part of embedded systems Abstraction of HW Resource management Meet real-time constraints Used in several low-power embedded systems Need for RTOS power analysis Significant power consumption Impacts application software power Re-used across several applications 8

9 Role of RTOS in embedded system Applications MPEG encoding ABS Communication Micro browser etc. Organizer IPC Timer Memory manager RTOS services Task manager Basic IO ISR Processor Memory Timer Other hardware Message composer Tasks Database Network interface Hardware 9

10 Related work and contributions Instruction level power analysis V. Tiwari, S. Malik, A. Wolfe, and T.C. Lee, Int. Conf. VLSI Design, 1996 System-level power simulation Y. Li and J. Henkel, Design Automation Conf., 1998 MicroC/OS-II: J.J. Labrosse, R & D Books, Lawrence, KS, 1998 Our work First step towards detailed power analysis of RTOS Applications: low-power RTOS, energy-efficient software architecture, incorporate RTOS effects in system design 10

11 Simulated embedded system IBM PT3 60 DRAM IBM PT3 60 DRAM EPROM LEDs Processor bus Fujitsu SPARClite On chip cache Timer UART Interrupts Other ASICs and peripherals Easy to add new devices Cycle-accurate model Fujitsu board support library used in model µc/os-ii RTOS used 11

12 Single task network interface Get packet Compute checksum Procure Ethernet controller Transfer packet Release Ethernet controller Checksum computation and output Procuring Ethernet controller has high energy cost 12

13 TCP example Checksum computation Get packet Compute checksum Buffer management Get packet Compute checksum Procure Ethernet controller Transfer packet Release Ethernet controller Output Procure Ethernet controller Transfer packets Release Ethernet controller Checksum computation and output Straight-forward implementation Multi-task implementation 13

14 Multi-tasking network interface Checksum computation Get packet Compute checksum Buffer management Output Procure Ethernet controller Transfer packets Release Ethernet controller RTOS power analysis used for process re-organization to reduce energy 21% reduction in energy consumption. Similar power consumption. 14

15 ABS example Y Sense speed and pedal conditions Timer transition? N Compute acceleration Brake decision Sleep Actuate brake 15

16 ABS example timing Timer Brake pedal ABS process Wheel sensor Brake action Time 16

17 Straight-forward ABS implementation Timer Y Timer transition? N Sleep Sense speed and pedal conditions Compute acceleration Brake decision Actuate brake Brake pedal ABS process Wheel sensor Brake action Time 17

18 Periodically triggered ABS Y Sense speed and pedal conditions Timer transition? N Compute acceleration Brake decision Sleep Actuate brake 18

19 Periodically triggered ABS timing Timer Brake pedal ABS process Wheel sensor Brake action Time 19

20 Selectively triggered ABS Pedal pressed? N Y Sense speed and pedal conditions Sleep Compute acceleration N Timer transition? Brake decision Actuate brake Y 20

21 Selectively triggered ABS timing Timer Brake pedal ABS process Wheel sensor Brake action Time 63% reduction in energy and power consumption 21

22 Power-optimized ABS example Timer Pedal pressed? N Y Sense speed and pedal conditions Brake pedal Sleep Compute acceleration ABS process N Brake decision Wheel sensor Timer transition? Y Actuate brake Brake action Time 22

23 ! k Infrastructure Application code OS code External stimulus SPARClite compiler Energy by call tree position for task A OSSched() main() OSSem() Timer model UART model Models for other peripherals SPARClite cache simulator SPARClite ISS Instruction level energy model Memory model Memory energy model Cache controller model Bus interface unit model 1s1s1s./ Energy by call tree position for task B 1B1B 23

24 À È Ž Experimental results Energy (mj) œ À ÀÀ È È Ç ÈÈ Ç È Ç ABS 1 ABS 2 Mailbox Semaphore Application Floating point Initialization Input/output Interrupt Mailbox Memory Misc. Scheduling Semaphore Sleep Synchronization Task control Net 1 Net 2 24

25 Ö Õ Ø è è è è Ú Ú è è Ú Ú è è Ú Ú è è Ú Ú è è Þ ÝÞ è è â ä ä Time (ms) TCP/IP 2 TCP/IP 1 ABS 1 ABS 2 Mailbox Semaphore ç ç ç ç ç ç ç Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë Ë ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÏÐ ÓÔ ÓÔ Ö Ø Ù Ù Ù Ù à ß à áâ ã Experimental results time Application Floating point Initialization Input/output Interrupt Mailbox Memory Misc. Scheduling Semaphore Sleep Synchronization Task control 25

26 Agent example Key Broadcast Price advertisement Sale Agent 1 Money Commodity 1 Commodity 2 Commodity 3 Commodity 4 Agent 6 Agent 3 Agent 2 Agent 5 Agent 4 26

27 ú ù þ ý ü ü Experimental results 8000 Energy (mj) ñòó ô óô Time (ms) õö ø ø ú þ û ÿ ÿ Application Floating point Initialization Input/output Interrupt Mailbox Memory Misc. Scheduling Semaphore Sleep Synchronization Task control (a) (b) 27

28 Experimental results Agent Application Floating point Initialization Input/output Interrupt mail tuned Ethernet Energy (mj) non buf buf Mailbox Memory Misc. Scheduling Semaphore Sleep Synchronization Task control (a) (b) 28

29 TCP example: 20.5% energy reduction 0.2% power reduction Optimization effects RTOS directly accounted for 1% of system energy ABS example: 63% energy reduction 63% power reduction RTOS directly accounted for 50% of system energy Mailbox example: RTOS directly accounted for 99% of system energy Semaphore example: RTOS directly accounted for 98.7% of system energy 29

30 Partial semaphore hierarchical results Function Energy/invocation (uj) Energy (%) Time (ms) Calls realstart init tvecs mj total init timer liteled % 5.51 mj total 1.74 % startup do main mj total save data % init data init bss cache on Task1 win unf trap mj total OSDisableInt % OSEnableInt sparcsim terminate OSSemPend win unf trap mj total OSDisableInt % OSEnableInt OSEventTaskWait OSSched OSSemPost OSDisableInt mj total OSEnableInt % OSTimeGet OSDisableInt mj total OSEnableInt % CPUInit BSPInit mj total exceptionhandler % printf win unf trap mj total vfprintf % 30

31 Energy per invocation for µc/os-ii services Service Minimum energy (µj) Maximum energy (µj) OSEventTaskRdy OSEventTaskWait OSEventWaitListInit OSInit OSMboxCreate OSMboxPend OSMboxPost OSMemCreate OSMemGet OSMemInit OSMemPut OSQInit OSSched OSSemCreate OSSemPend etc. etc. etc. 31

32 Conclusions RTOS can significantly impact power RTOS power analysis can improve application software design Applications Low-power RTOS design Energy-efficient software architecture Consider RTOS effects during system design 32

33 Impact of modern architectural features Memory hierarchy Bus protocols ISA vs. PCI Pipelining Superscalar execution SIMD VLIW 33

34 Summary Labs Simulation of real-time operating systems Impact of modern architectural features 34