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A File System for System
Programming in Ubiquitous
Computing
Christian Decker, Michael
Beigl, Albert Krohn
TecO, University of Karlsruhe
Institut for Telematics
Telecooperation Office (TecO)
www.teco.edu
Outline
Ubiquitous Computing and Devices
Development on Ubicomp Devices
File System Approach
Applications
Related Work
Conclusion
TecO File System for System Programming in Ubicomp, ARCS 2005 2
Ubiquitous Computing - Ubicomp
… building aware environments
AwareHome
(GATech)
Other areas
Safety applications AwareOffice
(TecO)
Military applications
TecO File System for System Programming in Ubicomp, ARCS 2005 3
Embedded Sensor Devices in
Ubicomp
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 File System for System Programming in Ubicomp, ARCS 2005 4
Ubicomp Development –
State-of-the-Art
Manage a variety of resources, esp. sensors
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 File System for System Programming in Ubicomp, ARCS 2005 5
Ubicomp Development –
Case Study
Study comprising of various students, practical courses and
projects
Findings
Experience lack
Huge number of various sensor interfaces
Developers are stuck to the well-known
Application complexity
Developer focus on distributed application logic
Rich sensor interfaces, poorly used
Interface breach
Sensor interfaces similar, only slight difference
Hard to realize -> debugging
TecO File System for System Programming in Ubicomp, ARCS 2005 6
File System Approach
Design principles Application
Developer in the center
Support developer to Name File System Type
follow the simplest way Space Operations File System 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 File System for System Programming in Ubicomp, ARCS 2005 7
Resources
Application
Name File System Type
Space Operations File System System
Direct Resources Mediated Resources
Detection
Actuators
unication
Sensors
Memory
Volume
Comm-
Battery
Status
Shock
Audio
...
Hardware
Microphone
Frontend
Memory
Radio
LEDs
TecO File System for System Programming in Ubicomp, ARCS 2005 8
Resources cont.
Application
Name File System Type
Space Operations File System System
Direct Resources Mediated Resources
Detection
Actuators
unication
Sensors
Memory
Volume
Comm-
Battery
Status
Shock
Audio
...
Hardware
Microphone
Frontend
Memory
Radio
LEDs
TecO File System for System Programming in Ubicomp, ARCS 2005 9
Name Space Name
Space
File System
Operations File System
Type
System
File = entity identifying a resourceDirect Resources Mediated Resources
Detection
Actuators
Directory = special file identifying collections of files
unication
Sensors
Memory
Volume
Comm-
Battery
Status
Shock
Audio
...
Uniform, hierarchical namespace
/dev/- direct resources, e.g. sensors, memory, power
supply, communication interfaceHardware
Microphone
/context/ - mediated resources, access direct
Frontend
Memory
Radio
LEDs
resources, application functions, algorithms
/usr/ - data files
TecO File System for System Programming in Ubicomp, ARCS 2005 10
Access Model Name
Space
File System
Operations File System
Type
System
Fundamental operations Direct Resources Mediated Resources
read(..) and write(..) – data transfer operations
Detection
Actuators
unication
Sensors
Memory
Volume
Comm-
Battery
Status
Shock
Audio
Resources are coupled with specific r/w methods ...
Resource Resource name Type Read Write VoltageSensorGet(int &v)
identifier
{
1 /dev/voltage 3 pFunc pFunc
Hardware ...
...
}
Example: read(1, buf, 1)
Microphone
Frontend
Memory
Radio
LEDs
NOP()
Additional operations {
open(..)
;
mount(..)/umount(..)
}
getType(..)
Type System
Type of resource, developer decides
Compatibility in resource combinations
TecO File System for System Programming in Ubicomp, ARCS 2005 11
Particle File System
File system for Particle platform
(Ubicomp device, sensor network)
18f6720 PIC microcontroller
128KB FlashROM, 4KB RAM,
512KB external Flash
Resources
Memory – 512KB Flash
Power supply – AAA battery
Wireless communication
Sensors – acceleration, light, force, temperature, audio,
ball switch
Actuators – LEDs, speaker
TecO File System for System Programming in Ubicomp, ARCS 2005 12
Application: Telnet
“/context/telnet/less /usr/file1“ Command Telnet Server Command
Parser Interpreter
Telnet Client
/context/telnet/less
ParticleFS
/usr/file1
Telnet Proxy /dev/comm /dev/eMem
Command
Parser
Communication Memory
file1 less
Particle Wireless
Wireless Stack Driver
Communication Network
PC Module
Network Direct
Resources Mediated Resources
UDP Network
... ... External
RF Frontend
Flash
Bridge Hardware
Particle
TecO File System for System Programming in Ubicomp, ARCS 2005 13
Application: Telnet cont.
Telnet application
Command Telnet Server Command combines resources
Parser Interpreter
“context/telnet/less“ is
/context/telnet/less a resource
ParticleFS
/usr/file1 Application function
/dev/comm /dev/eMem represented in the file
system
Communication Memory
“less” checks for type of
argument
file1 less
Wireless Stack Driver
Network Direct
Resources Mediated Resources “less” denies access to
/dev/accl, but grants
External
access to /usr/file1
RF Frontend
Flash
Hardware
TecO File System for System Programming in Ubicomp, ARCS 2005 14
Application: Over-the-Air-
Programming
Programming is file copy!
FTP Proxy
Compiled
Program
Network
Bridge
Particle
TecO File System for System Programming in Ubicomp, ARCS 2005 15
Performance
File system
~1900 bytes RAM
~2100 bytes ROM
File library
~10 kilobytes ROM
Access overhead
*buf = f()
Call + store result
26 instruction cycles
read(fd,buf,1)
lookup for function pointers + call + store result
More parameters
100 instruction cycles
TecO File System for System Programming in Ubicomp, ARCS 2005 16
Related Work
Plan9
All resources are files and accessed like files
Client/server concept
Dynamo, Context-aware file system (CFS)
Middleware and infrastructure solutions
Context-based sharing and visibility of data
PDA like devices
MatchBox, Micro-ROM
File systems for small embedded sensor devices
Only for data storage in files
TecO File System for System Programming in Ubicomp, ARCS 2005 17
Conclusion and Outlook
File system
Uniform resource representation (direct/mediated)
Uniform access on resources (read/write)
Combining resources (compatibility by type system)
Implementation on embedded sensor system (ParticleFS)
Applications: Telnet + Over-the-Air-Programming
Future work
Unblocking resource access
Represent remote resources
Shell/Macroprogramming
TecO File System for System Programming in Ubicomp, ARCS 2005 18
Thank you
Q&A
TecO File System for System Programming in Ubicomp, ARCS 2005 19
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