1. 1 of 14 1/15 Schedulability-Driven Frame Packing for Multi-Cluster Distributed Embedded Systems Paul Pop, Petru Eles, Zebo Peng Embedded Systems Lab (ESLAB) Linköping University, Sweden

2. 2 of 14 2/15... Factory Systems Heterogeneous Networks Distributed Heterogeneous System... Heterogeneous Networks Multi-Cluster Systems... NoCs Automotive Electronics...

3. 3 of 14 3/15 Distributed Safety-Critical Applications... Unsolved problems Gateway  Applications distributed over heterogeneous networks are difficult to...  Analyze (e.g., guaranteeing timing constraints)  Design (e.g., efficient implementation)  Applications distributed over the heterogeneous networks  Reduce costs: use resources efficiently  Requirements: close to sensors/actuators

4. 4 of 14 4/15  Design optimization  Several design problems can be addressed once an analysis is available. Contributions  Analysis and design of Multi-Cluster Embedded Systems  Analysis  Proposed a schedulability analysis for safety-critical hard real-time applications mapped on multi-cluster distributed embedded systems  Is the application schedulable? (Are deadlines satisfied?)  Bounds on the communication delays and communication buffer sizes  Design optimization  In this paper we have addressed the issue of packing application messages into frames (frame packing) for  Improving the degree of schedulability of an application  Reducing the hardware costs needed to run a schedulable application

5. 5 of 14 5/15 Outline  Motivation  Contributions  System architecture and application model  Related work  Schedulability analysis for multi-clusters  Frame packing for multi-custers  Experimental results  Message and future work

6. 6 of 14 6/15 S0S0 S1S1 S2S2 SGSG S0S0 S1S1 S2S2 SGSG TDMA Round Cycle of two rounds Slot Time Triggered Protocol (TTP)  Bus access scheme: time-division multiple-access (TDMA)  Schedule table located in each TTP controller: message descriptor list (MEDL) Controller Area Network (CAN)  Priority bus, collision avoidance  Highest priority message wins the contention  Priorities encoded in the frame identifier Hardware Architecture Gateway... Time-triggered cluster  Static cyclic scheduling  Time-triggered protocol Event-triggered cluster  Fixed priority preemptive scheduling  Controller area network protocol

7. 7 of 14 7/15 CPU NGNG Out CAN TTP Controller S1S1 SGSG Round2 P4P4 P1P1 CPU N1N1 TTP Controller MBI CPU MBI CAN Controller CPU N2N2 CAN Controller T m1m1 m2m2 m1m1 S1S1 SGSG Out TTP T P2P2 P3P3 Out N2 m3m3 m3m3 Software Architecture... Time-triggered cluster Event-triggered cluster Gateway

8. 8 of 14 8/15 Related Work  Frame packing for TT systems using TTP  H. Kopez, R. Nossal, The Cluster-Compiler – A Tool for the Design of Time Triggered Real-Time Systems, Workshop on Languages, Compilers, and Tools for Real-Time Systems, 1995  Frame packing for ET sytems using CAN  K. Sandström, C. Norström, Frame Packing in Real-Time Communication, Real-Time Computing Systems and Applications Conference, 2000  A. Rajnak, K. Tindell, L. Casparsson, Volcano Communications Concept, Volcano Communication Technologies AB, 1998  Frame packing for multi-clusters (ET + TT)  Has not been addressed previously  Cannot be solved separately for each cluster as inter-cluster communication creates a circular dependency

9. 9 of 14 9/15 Problem Formulation  Input  An application modeled as a set of process graphs  Each process has an worst case execution time, a period, and a deadline  Each message has a known size  The system architecture and the mapping of the application are given Application: set of process graphs... Architecture: Multi-clusterMapping  Output  Worst-case response times  A mapping of application messages to frames (frame packing) such that the application is schedulable  Mapping of ET messages to frames  Priorities for ET messages  Mapping of TT messages to frames  TDMA slot sequence

10. 10 of 14 10/15  Scheduling event-triggered activities:  Response time analysis: calculate worst case response times for each process  Schedulability test: response times smaller than the deadlines Schedulability Analysis  Scheduling time-triggered activities:  Building a schedule table: static cyclic scheduling (e.g., list scheduling)  Communication delays  Bounds on the buffer sizes  Response times depend on the communication delay between sending and receiving a message  Communication delays depend on the type of message passing 1.TTC  TTC 2.TTC  ETC 3.ETC  ETC 4.ETC  TTC

11. 11 of 14 11/15 Multi-Cluster Scheduling  Scheduling cannot be addressed separately for each type of cluster  The inter-cluster communication creates a circular dependency:  TTC static schedules (offsets)  ETC response times  ETC response times  TTC schedule table construction Application, Mapping, Architecture TT Bus Configuration Priorities Schedule Tables Response times Static Scheduling Multi-Cluster Scheduling Offsets Response Times Offset earliest possible start time for an event-triggered activity Bounds on the buffer sizes Response Time Analysis

12. 12 of 14 12/15 TTC TTP Gateway CAN ETC m 1 and m 2 packed in f 1, m 3 and m 4 not packed, deadline missed Frame Packing Example... TTC TTP Gateway CAN ETC Messages not packed deadline missed TTC TTP Gateway CAN ETC m 1 and m 2 packed in f 1, m 3 and m 4 packed in f 2, deadline met deadline

13. 13 of 14 13/15 Frame Packing Optimization Strategies  Simulated Annealing  Based on a simulated annealing approach  Cost function: degree of schedulability  Obtains near-optimal values for the degree of schedulability  OptimizeFramePacking  Based on a greedy approach  Cost function: degree of schedulability  Straightforward solution  Finds a schedulable application  Does not consider the packing of messages to frames

14. 14 of 14 14/15 Can We Improve Schedulability? 0 20 40 60 80 100 80160240320400 Average Percentage Deviation [%] Number of processes Simulated Annealing Near-optimal values for the degree of schedulability Straightforward solution Does not perform optimizations Cost function: degree of schedulability OptimizeFramePacking? OptimizeFramePacking

15. 15 of 14 15/15 Message and Future Work  Future Work  Explore more design problems  Mapping for multi-clusters  How to partition an application in ET and TT activities? Analysis and optimization methods are needed for the efficient implementation of applications distributed over interconnected heterogeneous networks.