Performance and results of the triple buffering built-in in a Raspberry PI to optimize the distribution of information from a Smart Sensor

11th International Symposium on Distributed Computing and Artificial Intelligence.Salamanca, 4nd-6th Juny, 2014

Performance and results of the triple buffering built-in in a Raspberry PI to optimize the distribution of information from a Smart SensorJose-Luis Jimenez-Garcia, Jose-Luis Poza-Lujan, Juan-Luis Posadas-Yagüe, David Baselga-Masia, José-Enrique Simó-TenSchool of Engineering in Computer Science (ETSINF)University Institute of Control Systems and Industrial Computing (ai2)Universitat Politècnica de València (UPV) (Spain


Why smart sensors?Use of sensors in robot navigation:

Survival behaviours reactive navigation simple sensorsComplex behaviours deliberative navigation has been used information from reactive information sensors

Currently, robots need sensors associated to behaviours.

However, this information is useful to build an environment map or to locate specific objects during the navigationThe information that a sensor produces is interesting it to be distributed to different behavioural processes


ComponentsFrom sensor to smart (intelligent) sensor (device)

Arduino

Intel Galileo

Raspberry PI

Reliability (and price)

Computing

Computing

Reliability (and price)

Temperature

PIR RGB-DSENSORS

CONTROLLERS+


ProblemsIntelligent sensor : pre-processing and Distributing the sensor data

Intelligent Sensor

RGB image

Depth map

Acquisition Process

···

Distribution

···

···

···

···

Clie

nts

Smart Resource

QoS


System

Real Robots

xTion

Raspberry Pi

USB

OpenNI

OpenCV

TCP Server

Ethernet

Smart Resource

Robots

TCP Client

Control

Simulation

Real implementation


Buffering techniquesSensor acquisition

Sensor distribution

Solution

1: Wait()2: Swap()3: Send()

1: I 0 2: Adquisition() frame3: while I < frame.MaxPixel do4: frame.Process()5: end while6: Swap()7: Signal()


Buffering

tacc < tdistributionAcquisition()

Process Thread()Process()

signal()

Send Thread()wait()swap() swap() send()

Clients

A1(fi+1)

A3(fi)

swap() & signal()

swap()

acquisition & process() send()

Intelligent Sensor

send()

send()swap() & signal()

send()

swap() & signal() send()

acquisition & process()


Frame A3 is last frame,

Frame A2 is not sent swap()acquisition & process()

send()swap() & signal()

..., fi, fi+1, fi+2, fi+3, fi+4, ...

A3(fi)

A3(fi)

A3(fi)

A1(fi+1)

A1(fi+1)

A1(fi+1)

A1(fi+1)

A1(fi+1)

A1(fi+1)

A1(fi+1)

A2(fi+2)

A2(fi+2)

A2(fi+2)

A3(fi+3)

..., fi, fi+1, fi+3, ...

A2(fi+2)

A3(fi+3)

A2(fi+4)

A2(fi+4)

A3(fi+3)

A3(fi+3)

A2(fx)

A2(fx)


Buffering

tacc > tdistribution

A1(fi+1)

A3(fi)

swap() & signal()

acquisition & process() swap() & send()

swap() & signal()



A3(fi)

A3(fi)

A1(fi+1)

A1(fi+1)

A2(fi+2)

A2(fi+2)

A2(fi+2)

A3(fi+3)

A3(fi+3)

A2(fx)

A2(fx)

wait()acquisition & process() A1(fi+1)

A2(fx)

A3(fi)

A3(fi)


acquisition & process() A2(fi+2)

A3(fi)

A1(fi+1)

wait()

swap() & signal() A1(fi+1)

wait()

swap() & send()

wait()

A1(fi+1)


A3(fi+3)

A1(fi+1)

A2(fi+2)

wait()

A1(fi+1)

A3(fi+3)

A2(fi+2)

wait()

swap() & send()

swap() & send()A1(fi+4)

A2(fi+2)

Acquisition()Process Thread()

Process()signal()

Send Thread()wait()swap() swap() send()

Intelligent Sensor

..., fi, fi+1, fi+2, fi+3, fi+4, ... ..., fi, fi+1, fi+2, fi+3, ...

Clients


Double buffer in front of triple buffering

Triple There is always a frame ready to be sentDouble Always sends the last frame

OptimizationTime

Triple buffer Send i

Acquisition & Process

Frame delay (i+2)

Frame Period

i+2 i+5

i i+3Double buffer Send

i+8

i+10 i+11i+9i+8i+7i+6i+5i+4i+3i+2i+1i

Frame delay (i+3)

i+9i+6


Real system to measure double vs triple buffering methods

Experiments

ControlDistributing


Smart sensor introduces a frame delay

Buffering vs number of clients

Results

1 client 2 clients 4 clients

Variables PC RPI PC RPI PC RPI

Simple buffer 67350 3176925 66936 592390 66945 1293636

Double buffer 67350 203086 66936 334824 66945 640506

Triple buffer 66940 199647 67386 332900 66930 611752

𝑇 𝑓𝑟𝑎𝑚𝑒𝑑𝑒𝑙𝑎𝑦=𝑡𝑎𝑑𝑞+𝑡𝑤𝑝+𝑡𝑝+𝑡𝑤𝑠+𝑡 𝑠


ConclusionsPowerful computer (PC) differences between the types of buffer are not significant.An embedded system provides less efficient results (delay times) but… Double buffer offers the last frame with some delay time. In triple buffering there is always a frame available to be sent.


Future workHow the buffer used affects to robot navigation? Reactive behaviours require information as quickly as possible so the triple buffer seems the most appropriate method. However, the immediacy of the double buffer, can improve certain non-critical behaviours as tracking paths, due to they provide latest information, but with less immediacy.As future work, it is planned to adapt the triple buffer to a system where the obtained data from the intelligent sensor would have several distinct parallel processes, in example, locating free paths to the robot trajectory at the same time that interesting objects to surrounding maps generation are detected like corners, walls or door steps.


Thanks for your attention