University of Kansas Douglas Niehaus Information and Telecommunication Technology Center Electrical Engineering and Computer Science Department University of Kansas Current Research Efforts in Real-time and Embedded Systems

University of Kansas Overview Real-time and Embedded Systems KURT-Linux Real-Time in Linux Component support for embedded configuration HW/SW Co-Design for Real-Time Future Integrated HW/SW Implementation Environment Group Scheduling Distributed Real-Time and Embedded Services

University of Kansas Real-Time and Embedded Systems Change many of the assumptions underlying conventional computer system design Real-time requires finer resolution time keeping and resource allocation because they must control when actions occur Precise control of events on real-time line When a computation executes is part of its correctness Execution time predictions are required in many cases Embedded systems are often special purpose Application semantics differ widely Specialized & Restricted semantics  specialized programming models No single programming model is best match for all application semantics  multiple models or lowest common denominator Majority of all computers (80%+) are embedded, increasing number must satisfy real-time constraints

University of Kansas Collaborators Douglas Niehaus Real-time, distributed, programming environments, systems David Andrews Real-time, embedded, architecture, HW design, sensor webs Jerry James Distributed, programming environments and models, formal methods Perry Alexander Formal Methods Rosetta (Modeling) Engineering of Computer Based Systems

University of Kansas KU Real-Time (KURT) Linux Long term effort to improve the suitability of Linux for real-time applications Modification for real-time within Linux Not a separate underlying executive as RTLinux and RTAI Three parts Time keeping and event scheduling (UTIME) KURT programming model Interrupt service (recent extension) Linux patch size is minimized

University of Kansas UTime: Time Keeping & Event Scheduling Portable High Resolution API Time Standard: Pentium Time Stamp Counter –CPU clock (nanosecond) resolution Next Event Interrupt: microsecond resolution –PC timer Chip (8159) or Pentium PIC Useful in its own right Often used without KURT component Starting point of Linux High Resolution Timers Project Multiple Platforms StrongARM, XScale/FPGA SBC, AMD Elan (x86+), Power PC (PPC) Virtex II Pro SBC (future) Time Standard and Next Event Interrupt methods vary

University of Kansas Data Streams Resolution of performance data must exceed that of the desired system behavior, not true of most aggregate data General method for representing and gathering data related to system status and performance Originally conceived for OS performance data (DSKI) Generalized to application programs (DSUI) Applications present significant interface challenges Data sources: Several types, multiple groupings Data Stream is generated by selected data sources Users choose which data sources to activate for a given experiment Configuration options on some data sources

University of Kansas DSKI Control and Data Flow

University of Kansas KURT: Programming Model Simple: explicitly designate execution intervals Using UTIME capabilities for time keeping and next event scheduling Primary Interface: Cyclic real-time execution plan Cyclic schedule repeats until deleted or replaced Easy to implement periodic computations Used to provide CPU percentage in a specific usage pattern (ANTS) Useful to guarantee event response times KURT module can switch dynamic schedules RTSS Scheduling server builds and submits new schedules in response to computation requests Conventional Linux Scheduler for non-real-time tasks Dynamically generated events in general timer queue

University of Kansas Basic KURT Architecture Hardware UTime KURT Programming Model OS User RT Scheduling Service Application Logging DSKI Plan Scheduler

University of Kansas Programming Model Framework Single programming model insufficient for the full range of real-time and embedded systems’ semantics Recent KURT-Linux extensions support creation of multiple components and configuration selection Scheduling decision functions Programming models Interrupt handling semantics System architects can select among existing components or implement their own Set of selected components determines system behavior

University of Kansas Programming Model Framework Hardware UTime OS User Logging DSKI Schedulers S1 S2S3S4S5 KURT Programming Models M1 M2M3M4M5 AAAAAAAA Real-TimeNon-Real-Time Interrupts DF1 DF2

University of Kansas Improving Interrupt Handling As Fast As Specified Rather than as fast as possible Interrupt handling currently manifests as noise in many RT programming models Interrupts are “always” enabled Handler notes which interrupts occurred Interrupt Decision function decides when handlers run Existing interrupt handlers supported for compatibility Exposes concurrency among interrupt handlers Currently one semaphore, but could be per-driver or per-data structure

University of Kansas Kernel Handler-Without ISR Mods

University of Kansas Kernel Handler – With ISR Mods

University of Kansas HW/SW Co-Design Supporting OS Functions Moving low level OS functions into hardware can: Increase quality of service, while Decreasing system overhead, and Increasing accuracy/predictability Several stages of CPU  FPGA migration Targets: Time Keeping and Event Scheduling (working) Event Queue (current) Thread scheduling (future) Interrupt Processing (future)

University of Kansas CPU-FPGA Cooperation for OS Support CPU FPGA JiffySub-Jiffy Time Standard Next Event INTR Jiffy Match Sub-Jiffy Match Memory Event Data Thread Data Event Queue Thread Scheduling Interrupt Subsystem

University of Kansas Conclusion System support for real-time and embedded programming environments is lacking in many ways KURT-Linux development has improved programming model support in several ways and improvement is continuing along several paths Current and future proposals in several areas DARPA PCES II award beginning now

University of Kansas Future Extend and generalize interrupt processing Minimize interrupt response time Parameterize speed/generality tradeoffs Modularize interrupt decision function –EDF for as fast as specified FPGA support HW/SW Co-Design programming environment NSF E&HS Proposal Group Scheduling DARPA PCES II Award Middleware System State Information Service Data Streams extension for OS and application state data DARPA PCES II Award

University of Kansas Future: HW/SW Co-Design Programming Integrated HW/SW programming environment Computations can flow easily across the HW/SW boundary FPGA based threads of computation have a simple standard interface for I/O and control Standard atomic semaphore operations are key CPU  FPGA FPGA  CPU Programming model will (largely) conceal support for a thread by CPU or FPGA HW/SW support choice can move later in the design and implementation flow

University of Kansas Future: Group Scheduling Generalized decision procedure for choosing a process (thread) to run next Linux uses one decision function and one group Our approach Decision function chooses among group members Threads are members of one or more groups Groups can be members of groups Decision Tree Start at the top and continue running group decision functions until next thread selected Should be able to integrate thread and interrupt scheduling in the operating system: fully integrated computation scheduling

University of Kansas More Information KURT-Linux Home Page: Data Streams Home Page: My Home page: Several Posters in ITTC Lobby