November 18, 2004 Embedded System Design Flow Arkadeb Ghosal Alessandro Pinto Daniele Gasperini Alberto Sangiovanni-Vincentelli We present a design flow for the design of embedded systems with control emphasis including software and the underlying computing platform and a case study for its application to a multi-media design: an MP3 player. We use Metropolis as integration environment and xGiotto as software design tool. Metropolis allows representing the functionality of the design and the architecture of the implementation platform in the same environment so that design exploration can be done quickly and efficiently. xGiotto provides a number of facilities that make software analysis and design easier by using a rigorous semantic approach that eliminates some of the most prominent reasons for errors and facilitates the correct implementation of the original control algorithm. The flow starts with xGiotto that is used as an input to the Metropolis environment. xGiotto designs are mapped to the Metropolis MetaModel. Platform architectures are directly input into Metropolis using the MetaModel natively. Mapping of the functionality to the architecture is performed in the Metropolis environment. The analysis of the mapped architecture can be used to feed back performance and other quantities related to the platform of interest to the software designer who then can modify the software to improve its design and to meet constraints. Functionality Capture Functional Simulation Quantity Estimation Formal Analysis Platform Selection Code Synthesis Platform Modeling Constraints Generation Mapping xGiotto Formal Verification xGiotto functional description xGiotto-to- Metropolis MMM functional description Mapping1 Mapping2 Mapping3 Platform1 Metropolis Description Platform2 Metropolis Description Platform3 Metropolis Description WCET Estimator Schedulability Results Simulator Platform Selection xGiotto Code Verification Code for the Target platform Platform Estimation External Storage Environment xGiotto Run-time System Task 1 xGiotto Program Description Task n Task 1Task n RTOS CPU BUS MEM Process Medium Quantity Manager CPU Arbitrator BUS Arbitrator Power Time Execution Time Task 1 Execution Time Task n Functional Mapping Architectural Event Filter Modified Embedded Machine Scheduler Environment SensorsActuators Platform active scope task completion execute E code task release xGiotto Reactions xGiotto Program Compiler Possible Execution Traces Code Generator Check Time Safety Check Race Safe Scheduling Strategy Not Safe Race Exists No Race xGiotto Tasks WCET map Run Time Implementation Compile Time Implementation Case Study (mp3 player) xGiotto-on-Metropolis Power and Energy estimation is done by Simplescalar-Arm Power Modeling Project Real-Time Operating System User Interface xGiotto Metropolis Framework Proposed Design Flow Integrating xGiotto and Metropolis in the Flow CPU BUS Memory Abstract Functionality Capture The embedded system application is captured using a real-time programming language Constraints Generation The constraints for execution are generated Platform Modeling The real-time platform characteristics are modeled Functional Simulation The functionality of the applications is studied to verify for desired behavior under test-case scenarios Quantity Estimation Platform dependent quantities (e.g. execution time) are estimated Formal Analysis Properties like races and schedulability are formally verified for the designed system Platform Selection Different platforms are explored and one of them is chosen based upon optimization criteria such as power and cost that involve the results of the estimation phase Code Synthesis Code generator produces code for the target platform xGiotto operational Semantics Denotational framework equivalent (using Tagged Signal Model) Equivalent Action Automata Model Equivalent MMM Language Model Basic Functionality Interaction Functionality Reaction Blocks - Basic programming blocks in xGiotto - Consists of release statements and trigger statements and a termination event - Releases tasks and invokes triggers » react {reaction block} until [event]; Schedule Instruction – Schedule tasks – Tasks are released with the invocation of the reaction block – Tasks are terminated with the termination of the reaction block » release task (input ports) (output ports); Trigger Statements – Defines the invoking action associated with an event » when [event] reaction block; – Repetition construct using whenever active releasestartpreemptionresumecompletiontermination running release eventtermination event completion event Logical Execution Time (LET) { { Physical Logical Race Condition Detection Verifying whether a program variable is updated with multiple values and thus leading to non-determinism Resource Size Analysis Predicting run-time memory requirements for executing an xGiotto program Schedulability Analysis Ensuring that all task invocations get access to the executing platform at least equal to their worst-case- execution-times before their termination Programming language targeted towards event driven control applications The language is based on Logical Execution Time (LET) model of tasks The programmer specifies when the output of a task becomes available Event Scoping Events are the main structuring principle Event can be implicitly scoped by program definition A scope can be active: events are handled as soon as they occur passive: events are ignored or remembered so that the related action is taken when the surrounding scope becomes active again Language Features LET model Analysis xGiotto Run-time and Compile Time Implementation Implemented on Lego Mindstorm RCX unit Two different hardware configuration are tested: -- ARM processor using simplescalar ISS -- PowerPC 750 processor using ppc750sim ISS Flash Memory task dac -- reads buffer with the decoded stream task read -- accesses the external storage task decode -- decodes the stream stored in buffer task battchk -- checks battery life task tempo -- modifies the speed of the song task pitch -- modifies the pitch and key task rate -- changes both the tempo and pitch task vol -- updates the volume task editlist -- edits the list of songs to be played task skip -- skips songs to be played task usb -- downloads songs into the player xGiotto run-time system is implemented on Motorola coldfire m68k Execution time analysis and power measurements for the tasks on different platforms