Ubiquitous Resources Abstraction using a File System Interface on Sensor Nodes
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Ubiquitous Resources Abstraction using a File System Interface on Sensor Nodes

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  • - computation embedded in the physical world

Ubiquitous Resources Abstraction using a File System Interface on Sensor Nodes Ubiquitous Resources Abstraction using a File System Interface on Sensor Nodes Presentation Transcript

  • Ubiquitous Resources Abstraction using a File System Interface on Sensor Nodes Till Riedel, Christian Decker TecO, University of Karlsruhe Institut for Telematics Telecooperation Office (TecO) www.teco.edu
  • Outline Analysis Design of a Resource Abstraction Evaluation Applications TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 2
  • Embedded Sensor Devices inUbicomp Motes Particles Telos Limited computing power, 8-bit microcontroller Few kilobytes … 512 kilobytes of Flash memory Customized radio protocols Battery powered Extensible by various sensors TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 3
  • Analysis Big variety of sensors Growing APIs Experiences with developers  Hesitate to develop code for „new“ sensors  Stick to the stuff they know  Use example program TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 4
  • Ubicomp Development –State-of-the-Art Lightweight OS (e.g. TinyOS)  OS shields resources, e.g. sensors  No direct access  Communication through events -> event dispatching Library based access models  Abstract access functions  Direct access, virtually no overhead But… shielding/abstraction causes still confusion TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 5
  • File System for Sensor NodesDesign principles Application Developer in the center Support developer to Name File System Type File System follow the simplest way Space Operations System Easy-to-understand interfaces -> generic Direct Resources Mediated Resources Detection Actuators unication Sensors Memory Volume Comm- Battery Status Shock Audio ...Support in two ways Uniform representation of all resources Uniform access model Hardware Microphone Frontend Memory Radio LEDs TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 6
  • File System InterfaceOperation Explanationsize_t read Reads n data bytes from the resource identified by fd (int fd, void* buf, size_t n) to buf; returns number of bytes or -1 if error occurredsize_t write writes n data bytes from buf to the resource fd; returns (int fd, void* buf, size_t n) number of bytes or -1 if an error occurredint open(char* resource_path) Returns a descriptor for the resource; -1 if it is not valid.int close(int fd) Frees the descriptor of a resource; -1 if fd is not validint getType(int fd) Returns the type of a resource fd; -1 if fd is not valid.int mount Creates a resource in the name space. Type and (char* resource_path, int type, function pointers to their specific read and write (*pFunc) read, (*pFunc) operations are given. -1 is returned if thewrite) resource_path already exists.int umount(char* resource_path) Removes a resource; -1 is returned if it is not valid. TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 7
  • Namespace and Ressources Mount Table name type read* write* Name Space Table 0 audio 6 readMic setRate0 /dev 1 audiovolume . calcVol setRange1 /light ... ... 3 ... ...2 /audio n-1 light readLight nop3 /usr n [free]4 /file15 /subdir6 /file27 /audiolib Storage Table8 /audiovolume name type read* write*9 [free] 0 file1 writeFile readFile 1 file2.frag ... 1 2047 [free] 2048 file2 TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 8
  • File System – Access ModelName space Hierarchical Textual representation of fd= o p en(”/ com /rf”) resources read write state typ e com rf Combine freely resource fil desc rip tor e rf d river and specific behaviorStreams write(fd ,...) Access functions “read”, “write” read write state typ e Sequential access  enforced by state rf_ read rf_ write 0 21 3 Pass data between streams -> Stacking of streams TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 9
  • Hardware TecO Particle Computer 18f6720 PIC microcontroller 128KB FlashROM, 4KB RAM, 512KB external FlashResources Memory – 512KB Flash Power supply – AAA battery Wireless communication Sensors – acceleration, light, force, temperature, audio, ball switch Actuators – LEDs, speaker TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 10
  • Optimization Paralallize write operations (Flash Buffer, Flash, EEPROM) 13 ms Flash, 4 ms EEPROM, assynchronously programmable Mimimize writes on Flash/EEPROM only 50.000-100.000 erase/write cycles per page Minimize read times for sensor devices support relatively high sampling rates / bytewise sampling Minimize RAM consumption only 4K of RAM available TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 11
  • PerformanceAccess overhead cycles PIC18F6720Table look up function 15 cycles 3 µsDereferencing state 4 cycles 0.8 µsPassing Parameters 10 cycles 2 µsFunction pointer call 26 cycles 5.2 µsAccessing Parameters 10 cycles 2 µsWriting the buffer 15 cycles 3 µsReturning 13 cycles 2.6 µsOverhead of file system read 93 cycles 18.6 µsOverhead of simple Library call 26 cycles 5.2 µsRelative overhead 67 cycles 13.2 µsTecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 12
  • PerformanceMemory Consumption File library  2 byte on flash per resource (129 per page)  12 byte per file descriptor (3 byte state)  Non-Persistent ressources ▫ 6 byte + name in RAM + Library Code in internal flash ▫ about 12 KB (10%) ▫ 6K without persistent storage TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 13
  • Integration of persistent storage Simple flash FS Sequential append-only files Non-blocking operation Uncontrolled extrusionTecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 14
  • Application - Integration CompiledFTP Proxy Program Seamless transfer of data between backend infrastructure PC and sensor nodes Composition of name spaces using URI scheme ste;1;33 ^C FTP Proxy Network Programming is file copy Sensor logging is downloading Bridge Particle TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 15
  • POSIX interfaceApplications can be easily portedlibc standard I/O  fprintf  stdoutcompliant C Programming EnvironmentTecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 16
  • Application - ShellFile system as interactive runtime environment“cat audiovolume“ Application Command Shell ParticleFS Reources cat audio audioVolume Direct Resources Mediated Resources Hardware Microphone TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 17
  • Application - ShellFile system as interactive runtime environment Standard output as context Popping stack elements from pipe stack TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 18
  • Asynchronous InteractionService /service/ resultClientSimple IPC mechanism TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 19
  • Dynamic Loadable Modules No linking of function calls needded Specify fixed location for  file descriptor table  open  mountFunctionality instantly available after mountHot code replacement TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 20
  • Thank you.TecO KuVs FG System Software für Pervasive Computing 2005, October 12, 2005 21