Support for a reconfiguration DSL in highly constrained embedded systems. Juraj Polakovic, Sebastien Mazaré, Jean-Bernard Stefani Séminaire SARDES

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1 Support for a reconfiguration DSL in highly constrained embedded systems Juraj Polakovic, Sebastien Mazaré, Jean-Bernard Stefani Séminaire SARDES

2 Dynamic Reconfiguration in constrained embedded systems Dynamic Reconfiguration modifying a system s architecture and behavior during its execution error-prone - architectural and behavioral integrity must be guaranteed OS for small ( deeply ) embedded devices memory size (~4-8kb RAM, kb Flash, Harvard architecture) computing power (cpu ~ 8-16Mhz) -> strong interrupt timing contraints flash for kernel code power consumption (ex. standalone system on batteries) maintainance can be difficult (ex. deployed in the nature) How to provide safety of reconfigurations in constrained OS? France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

3 Our approach Fractal/Think for building OS component as run-time entities model is hierarchical -> variable granularity of reconfigurations dynamic reconfiguration mechanisms ADL reperesentation of the running OS (other binary meta-data could be included in this ADL) FScript for writing reconfiguration programs based on the ADL France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

4 Use a native FScript interpreter (ie in C) Problem : cost of the interpreter memory + code size too prohibitive dependent on the nature of the verifications inflexible (eg if we want to add a supplementary verif, we have to change the interpreter) France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

5 Offload the FScript compilation to a remote host 2 other alternatives: France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

6 From an FScript reconfiguration program to its execution Compile Fscript reuse the original FScript interpreter, integrated to FractalADL run the reconfig. program on a representation of the target system (=initial ADL) log the actual results, corresponding to the reconfiguration actions transform the log into C reconfiguration code => reconfiguration component Packaging: Reconfiguration component + new components reconfiguration component compiled with the Think compiler packaged as a loadable ELF file (gcc + ld) Load and Execute the reconfiguration component - minimal support on the target device communication link dynamic loader, linker FScript helper functions (code factorisation) France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

7 Results Run-time on the target platform minimal communication link loader FScript helper functions Reconfiguration code is minimal only log from FScript, thus real reconfiguration actions Component packaging (new components + reconfiguration code) relatively important overhead due to the ELF format due to the structure of the C code generated by the Think compiler thanks to optimizations, this could be solved Last minute result Reconfiguration with dynamic loading on an AVR platform (8k RAM) Binary meta-data from the initial kernel image Pre-linked object files sent to the device (no ELF, linking thanks to meta-datas) France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

8 Conclusion We did it! internship of Sebastien Mazare prototype on ipaq, prototype on an AVR should be finished until end 2006 submitted to EuroSys2007 Difficulties to support this approach on a severely constrained flashbased architecture problem: dynamic linker for a flash-based system requires either too much memory to link (we do not have) or to pre-link the code (could require a complex meta-data retrieval protocol to determine the link adress) Lots of open issues external configuration representation and meta-data packaging format (ELF, binary ) France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

9 Travaux en cours Objectif thèse: Fournir un modèle de programmation de systèmes reconfigurables Eléments du modèle Fractal/Think pour construire des OS reconfigurable ADL élément pivot Spécification de parties de l OS reconfigurable et avec quels mécanismes Spécification du mapping au modèle d exécution (multi-thread vs. event-based) FScript pour écrire des programmes reconfigurables Travaux en cours Optimisations architecturalles Modèle événementiel (mapping vers le eventscheduler existant) en attente d optimisations pour faire les benchmarks (Réversibilité des optimisations?) France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/

10 France Telecom R&D Division Support for a reconfiguration DSL in highly constrained embedded systems, Seminaire SARDES 22/11/