Announcements Reprogramming HW2: Due on 3/16 (Wed), 2:30pm Mat: - - PDF document

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Announcements

• HW2: Due on 3/16 (Wed), 2:30pm
• Hard deadline!
• Midterm
• Open book, note

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Middleware for Wireless Reprogramming

• Maté: mobile code
• Agilla: mobile agent

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Motivation for Mobile Code

• Need to reprogram sensors after deployment
• Change parameters
• Change/add/remove modules
• Change whole program
• Manual installation on a large number of nodes

is impractical

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Summary: Maté

• Instruction Set
• Concise: utilizes the least amount of network

bandwidth

• Tailorable: can be modified for special operations
• Virtual Machine
• Small footprint: fits in rene2 (1KB data, 16KB code)
• Resilient: cannot crash the mote
• Energy: tradeoff between deployment and execution

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Limitations of (Just) Mobile Code

• Whole network runs one application
• Cannot adapt to changes in
• Goals
• Environment
• Network
• Lack coordination between nodes

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Mobile Agents : A Motivation Example

1 2 3 4

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Agilla Approach

• Agent mobility
• Clone and move to designated physical

locations

• Inter-agent coordination
• Operations on local and remote tuple

spaces

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System Architecture

TinyOS

Node (1,1)

Tuplespace Neighbors

Agilla Middleware MICA2 Mote Agents TinyOS

Node (2,1)

Tuplespace Neighbors

Agilla Middleware MICA2 Mote Agents

migrate remote access Chenyang Lu CSE 467S 9

Location-Based Addressing

(3,1) (3,2) (3,3) (2,2) (1,1) (1,3)

clone(3,3) clone(3,1)

Fire Detection Agent

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Agent Migration

• Two types of migration instructions:
• Move: smove, wmove
• Clone: sclone, wclone
• Two variants of each:
• Strong
• Weak

move(3,4)

clone(4,6) clone(3,5)

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Tuplespace-based Coordination

• Inter-agent coordination done through tuple spaces
• Shared memory interface
• Pattern matching using tuples
• Shared locally, accessible remotely

Tuplespace

OUT(< string: fir> ,< loc: 1,1> ) IN(< type: string> ,< loc: 1,1> )

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Tuplespace Instructions

• out: insert
• in: remove
• rd: read
• inp: probing remove
• rdp: probing read
• rout: insert
• rinp: probing remove
• rrdp: probing read
• rrdpg: probing group

read of all neighbors Local Remote Note: all are non- blocking, rrdpg saves results on heap blocking

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Examples

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Example: Fire Tracking Agent

• If a neighbor is on fire
• Clone to all neighbors within 1.4 grid hops
• f the fire
• Periodically repeat to maintain dynamic

perimeter

• Sleeps 1.25 – 6 seconds during each epoch

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Agilla Conclusions

• New paradigm for programming sensor

networks

• flexible coordination
• adaptive and open software structure
• reasonable performance
• Demonstrated feasibility of mobile agents in

sensor networks

• Todos
• Better programming models
• More real-world experience
• Security

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Readings

• P. Levis and D. Culler, “Maté: a Virtual Machine for Tiny

Networked Sensors.” ASPLOS, Dec 2002.

• (Strongly recommend) C.-L. Fok, G.-C. Roman, and C. Lu, "Rapid

Development and Flexible Deployment of Adaptive Wireless Sensor Network Applications," ICDCS, June 2005.

• Chien-Liang Fok, Gruia-Catalin Roman, and Chenyang Lu, "Mobile

Agent Middleware for Sensor Networks: An Application Case Study," IPSN/SPOTS, April 2005.

• Agilla Project: http://www.cs.wustl.edu/mobilab/projects/agilla/

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Operating Systems

• TinyOS
• Real-time POSIX
• Real-time schedulability analysis

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Real-Time POSIX

• Standard of UNIX
• Supported by many operating systems
• Variants of UNIX
• Linux
• Many commercial RTOS, e.g., VxWorks
• Windows provides similar services

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To Be Covered

• Supervisor mode
• Process management
• Scheduling
• Race condition

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Supervisor mode

• On processors with supervisor mode, you can do the

following only in supervisor (kernel) mode

• Execute privileged instructions and access special hardware
• Set real-time priority
• Device driver
• Access to a separate address space (the kernel space)
• This is the mode in which the operating system usually runs.
• Provide protective barriers between programs.
• Prevent applications from corrupting OS data.

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Supervisor Mode (2)

• Careful about memory access (e.g.,

pointers) when

• programs run in supervisor mode
• Or processor has no supervisor mode
• Support supervisor mode?
• SHARC, ATMEL: No
• Pentium, ARM: Yes

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ARM supervisor mode

• Use SWI instruction to enter

supervisor mode, similar to subroutine:

SWI CODE_1

• Sets PC to 0x08.
• Argument to SWI is passed to

supervisor mode code.

• Saves CPSR in SPSR.

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Trap

• Trap (software interrupt): an exception

generated by an instruction.

• Ex. enter supervisor mode.
• Ex. call a service routine
• ARM uses SWI instruction for traps.
• SHARC offers three levels of software

interrupts.

• Called by setting bits in IRPTL register.

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Exception

• Exception: internally detected error.
• Exceptions are caused by instruction

execution

• unpredictable
• Build on top of interrupt mechanism.
• Exceptions are usually prioritized and

vectorized.

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Terms

• Interrupt: generate by external devices
• Exception: generate by CPU due to

software errors

• Ex. div by 0
• Trap: generate by software using

instructions (enter supervisor mode:

• pen file, read from network etc.)