Embedded Systems Engineering Armin Wasicek fileOne active master per cluster ... Each node has its own RODL (part of a ‘big picture’) RODL must be consistently defined over all

Smart Transducer Networks

Embedded Systems EngineeringArmin Wasicek

Overview

Motivation & Design Principles TTP/A Fieldbus Protocol Implementation Requirements Smart Transducer Interface Standard Conclusion

TTP/A Smart Transducer Networks 2

Definition

A smart transducer is the integration of an analog or digital sensor or actuator element, a processing unit, and a communication interface.


MCU

NetworkInterfacePhysical

TransducerDigitalCommunicationSystem

Smart Transducer

Motivation

Sensor/Actuators become more complex (e.g. providing various modes of interfacing, operation...)

Requirement for fault-tolerant and distributed systems -> networked sensors and actuators

Embedded microcontrollers can handle complexity at a fair price

Cheap mass-production of flexible general purpose smart transducers


Design Principles for ST (1)Two-Level Design Approach


• Node level:

– Transducer developer handles sensor- and actuator-specific details

– Functionality of transducer is exported via well-specified interface

• System level:

– System integrator can handle node as black boxes and build on exported services

• Composability principle guarantees that services, which are established at node level are maintained at system level

Three Interfaces of a Node


SPLIF … Service Providing Linking Interface

SRLIF … Service Requesting Linking Interface

Design Principles for ST (2)Real-Time Service

Knowledge about the exact instant of an event Predictable timing with low jitter (control loops) Guaranteed timing behavior under load and fault

hypotheses


Design Principles for ST (3)Diagnosis & Management Support

Diagnosis access to ST internals Not necessarily real-time capable Monitoring support without a probe effect on real-time

service


Design Principles for ST (4)Configuration & Planning Support

Machine-readable description of ST properties Automated configuration saves time Required qualification of personal can be lower Fewer configuration faults, since monotone and error-

prone tasks are done by computer


Overview

Motivation & Design Principles TTP/A Fieldbus Protocol Implementation Requirements Smart Transducer Interface Standard Conclusion


TTP/A Protocol (1)

One active master per cluster Up to 250 slaves Communication organized in rounds TDMA bus allocation


For details see:

TTP/A Smart Transducer Programming –A Beginner’s Guide

Available at: (http://www.vmars.tuwien.ac.at/)

Publication & Research Reports

TTP/A Smart Transducers 12Time Division Multiple Access

TTP/A Protocol (2)

Interface File System (IFS) (1) Hierarchical distributed data structure Source and sink of each communication Unique addressing scheme:

Cluster (0..255)Node (0..255)

File (0..63)Record (0..255)

Byte (0..3) IFS maps all relevant properties (sensor and actuator

data, calibration parameters, configuration data, serial number, …)


Interface File System (IFS) (2)

Header Record

First record of each file contains status information (access permissions, file length, etc)

Special Files

Documentation file: physical name of node (similar to MAC address)

Configuration file: logical name of the node, current fireworks-byte, epoch-counter etc.

Round Descriptor List (RODL): holds information about actions performed by a node for a particular round

Round Sequence file (ROSE): specifies sequence of rounds, only implemented in the TTP/A master


Round Types Master-slave round: Master accesses a record by broadcasting its IFS address and a

tag indicating operation (read, write, …) Master-slave address (MSA) and master-slave data (MSD) part

Multipartner round: TDMA communication is predefined by RODL Up to 6 different modes (predefined schedules)


Round Description List (RODL)

For each slot in each round:

Operation (receive, send, receive and synchronize clock, execute)

Data source/sink (IFS address + message length)

Each node has its own RODL (part of a ‘big picture’)

RODL must be consistently defined over all nodes

RODL itself is accessible via IFS


Common Communication and Action Schedule


1 2 3 4

A Send Receive Receive ExecuteB Receive Send Receive SendC Receive Receive Send ReceiveD Receive Receive Execute Receive

slotnode

t

Realization of Three Interfaces (1) Real-Time Service (RS): Multipartner rounds

Configuration and Planning (CP) Interface Master-Slave rounds accessing RODL

Diagnostic and Maintenance (DM) Interface Master-Slave Rounds during operation


Realization of Three Interface (2)

RS Interface: IFS realizes Service Requesting Linking Interface (SRLIF) and Service Providing Linking Interface (SPLIF)

CP Interface: access via RODL

DM Interface: local data of individual TTP/A tasks (stored in service file)

SRLI

F SPLIF

CP DM

ServiceRT Input RT Output

Local Interfaces


TTP/A Example Three TTP/A nodes

Node 0 is the TTP/A master (synchronization of slaves via fireworks byte)

Node 3 executes in slot 0x03 a counter and broadcasts the actual value in slot 0x01

Node 2 receives the counter value in slot 0x01 and displays the new value in slot 0x03 (also by executing a TTP/A task)

Inter-round gap (end of round) in slot 0x07

In the following the code of node 3 is illustrated

The example is available on the Lab homepageTTP/A Smart Transducer Networks 20

TTP/A Example: IFS Layout


TTP/A specific include files

e.g. IFS access macros

name of the IFS file for the application

(suggested range 0x30 to 0x3d)

memory section for IFS storage (ifs_int_eep

… EEPROM)

(ifs_int_0 … zero initialized SRAM)

layout of the application file

IFS address

signed 8-bit int value for incr. value

unsigned 8-bit value for error code

declaration of TTP/A task

TTP/A Example: RODL Layout


TTP/A specific include files

e.g. IFS access macros

layout of the RODL (for node 3 only)

RODL filename (0x00 to 0x07); length of RODL; memory

section for storage (EEPROM)

operation: send

slot: 0x01

IFS addr: I/O file record 0x01, byte 0

length: 1 (len – 1 is stored)

operation: execute

slot: 0x03

IFS addr: specifies the task to execute

end of round: slot 0x07

TTP/A Example: Node Source-Code


application file with initialization

pointer to I/O file = I/O file

increment value = 1; error flag = 0

I/O file

parameters for file definition:

file number, variable name, TTPA/task, file length, memory section, and access mode

code for TTP/A task

code for initialization function

adding an initialization function:

task handle, function pointer to task, order, execution states

adding a background task is similar

Overview

Motivation & Design Principles TTP/A Fieldbus Protocol TTP/A Implementation / Case Study Smart Transducer Interface Standard Conclusion


Architectural Requirements

Standard UART (may be also a software UART)

About 2KB ROM for protocol code

About 32 byte RAM for protocol-specific variables (e.g., RODL memory)

Supports any serial bus


Case Study Hardware


Atmel AVR TTP/A nodes

PCMCIA Master/Gateway

Case Study Software

RODL design tool Written in Java => Platform-independent Connects to cluster via CORBA interface

Monitoring tool Displays contents of node’s IFS Refreshes data periodically Connects directly via RS232 Important for lab course


Overview

Motivation & Design Principles TTP/A Fieldbus Protocol TTP/A Implementation / Case Study Smart Transducer Interface Standard Conclusion


OMG Smart Transducer Standard

Specifies a CORBA interface for accessing the IFS contents of a TTP/A cluster remotely

Specifies IFS addressing scheme

Specifies real-time communication

CORBA can be used for configuration and monitoring

Access to real-time service interface possible, when a RT-CORBA is used


Example Architecture


Overview

Design Principles TTP/A Fieldbus Protocol Implementation Requirements Smart Transducer Interface Standard Conclusion


Conclusion Two-level design for ST applications

Node level: transducer details System level: integration to overall system

TTP/A: Master/Slave protocol supporting periodic real-time

traffic and sporadic diagnostic and management communication

Low-cost, highly-efficient (no addressing overhead)

Standardized CORBA interface supports remote tool access


Vielen Dank für Ihre Aufmerksamkeit!

Fragen?


Documents

Embedded Systems Engineering Armin Wasicek fileOne active master per cluster ... Each node has its own RODL (part of a ‘big picture’) RODL must be consistently defined over all