Idea Transcript
Department of Electronics School of Informatics, Electronics, and Telecommunication AGH Univ. of Science & Technology in Krakow
Embedded Systems in Industrial Automation from single node to networked embedded systems Richard Zurawski
Lulea, February 18, 2015
Outline Embedded systems in industrial automation Networked embedded systems Design issues Node design & technologies Network design & technologies Timing & schedulability Wireless Sensor Networks and technologies
Richard Zurawski, Lulea, Feb. 18, 2015
Embedded Nodes
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Embedded Nodes
Richard Zurawski, Lulea, Feb. 18, 2015
Embedded Nodes
point-to-point
multidrop Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Outline Embedded systems in industrial automation Networked embedded systems Design issues Node design & technologies Network design & technologies Timing & schedulability Wireless Sensor Networks and technologies
Richard Zurawski, Lulea, Feb. 18, 2015
Networked Embedded Systems
There have been various reasons for the emergence of networked embedded systems, influenced largely by their application domains. Some of the most important ones: ● the benefits of using distributed systems ● evolutionary need to replace pointto-point wiring connections in these systems by a single bus
Richard Zurawski, Lulea, Feb. 18, 2015
Richard Zurawski, Lulea, Feb. 18, 2015
Networked Embedded Systems
A networked embedded system is a collection of spatially and functionally distributed embedded nodes interconnected by means of wireline or/and wireless communication infrastructure and protocols, interacting with the environment (via a sensor/actuator elements) and each other (peer-to-peer), and, possibly, a master node performing some control and coordination functions to coordinate computing and communication in order to achieve certain goal(s).
Richard Zurawski, Lulea, Feb. 18, 2015
Networked Embedded Systems
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Networked Embedded Systems
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Elements & Aspects ● ● ●
Nodes Communication Links (Specialized Communication Networks) Real-time
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Smart Transducers
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Specialized Communication Networks
wireline networks; using media such as: ● ● ●
twisted pair cables, fiber optic cables, power lines
currently in wide use tens of specialized communication networks and protocols developed for a variety of application areas with functionalities dictated by different requirements on payload, speed and bandwidth, delay and jitter, dependability, …
Richard Zurawski, Lulea, Feb. 18, 2015
Wireline Networks
wireline networks; using media such as: ● ● ●
twisted pair cables, fiber optic cables, power lines
currently in wide use tens of specialized communication networks and protocols developed for a variety of application areas with functionalities dictated by different requirements on payload, speed and bandwidth, delay and jitter, dependability, …
Richard Zurawski, Lulea, Feb. 18, 2015
Wireless & Hybrid Networks wirelss networks; supporting radio frequency channels (EMF), and infrared connections ● ●
IEEE 802.11/WLAN, IEEE 802.15.1/Bluetooth, IEEE 802.15.4/ZigBee, …
hybrid networks; wireline extended by wireless links
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Real Time ... real-time systems (real-time operation) - in which systems are required to respond to changes in the environment the system is embedded in, or interacts with, within a predefined period of time mandated by the dynamics of that environment Response: ● ● ●
periodic aperiodic sporadic
System classification: ● ● ●
soft real-time hard real-time safety critical hard real-time
Richard Zurawski, Lulea, Feb. 18, 2015
Outline Embedded systems in industrial automation Networked embedded systems Design issues Node design & technologies Network design & technologies Timing & schedulability Wireless Sensor Networks and technologies
Richard Zurawski, Lulea, Feb. 18, 2015
Design Issues
1) Node(s) design 2) Network design 3) Timing and Scheduleability Analysis
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues - Modularity Modularity – to improve maintainability: ● ●
Modifications fixing bugs
● ●
Implementations of new functionality upgrades to new SW/HW versions
Pros
Cons
Re-use elements
Minimized development effort due to reuse of HW/SW design (and code)
Lower performance (footprint, response time, power consumption, etc.) due to increased overhead
Risk reduction
Design based on well-proven and tested components
Integration of several components can result in unclear/untested behavior
Migration
Minimized effort to migrate to other (newer) SW/HW versions
Lower performance due to “wrappers” needed to maintain system interfaces
Aspect
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues - Modularity
HW vs. SW Components Single vs. multiple chips
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues - Modularity
IC Interfaces: Exchanging integrated circuits (ICs) requires their interfaces to be compatible - pin compatibility: ●
●
●
functional compatibility - two ICs have the same functions (inputs, outputs, power supply, ground, etc), assigned to the same pins. mechanical compatibility - ICs can be inserted into the same socket or soldered to the same footprint. electrical compatibility - components work with the same supply and signaling voltage levels.
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design Important for wireless sensor nodes Microcontroller - several controllable low power modes. External Real-Time Clock (RTC) - can be powered on and off Radio chip - provides on/off control, as well as a reset possibility. Analog filter electronics can be powered on and off. sleep/wakeup mode – transmission only on the “delta” change Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design
Texas Instruments MSP430 variant can be operated at voltage levels ranging from 1.8 to 3.6 V, and supports five low power modes. When operating at a 3.0 V supply level: ●
in the lowest power-saving mode (the CPU is practically turned off) typically requires 0.1 µA,
●
in standby mode (next lowest) it requires 1.6 µA,
●
in active mode it requires 400 µA.
The drawback with the “off” mode is that the CPU can only wake up from an externally generated interrupt
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design
MSP430 settling time - the time it takes for the CPU to become fully operational when waking up from a power save mode: ● ●
“off” mode - 6 µs standby mode - 6 µs
the “off” mode allows to further decrease power consumption by shutting off the RTC However, without the RTC signal, the CPU will default to an inaccurate, internal, lower frequency clock. Thus, when waking up from the “off” mode, the RTC oscillator signal has to be activated before the CPU will stabilize, which adds to the 6 µs wakeup time.
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design
HMI local HMI may be required to: check the status, calibrate, command the device to perform a measurement. Depending on the requirements on packaging, or the available power budget, several alternatives are used in the industry ranging from simple LEDs and buttons to LCDs.
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design Energy Efficient Protocols communication protocol has a major impact on the final power consumption of the system Media access scheme: ●
●
TDMA – no collisions, or minimized – no need for retransmission due to collisions CSMA - the node first has to listen before it can send its data, which degrades rapidly when there is lots of communication
Data package size
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design Energy Efficient Protocols Topology:
Single-hop topology - avoids delays in intermediate nodes
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Low Power Design Energy Efficient Protocols Topology: Multi-hop topology: a node may have to wake up to forward data from other nodes intermediate nodes don’t know when they may be called upon to route packets for others intermediate nodes (router nodes) to be mains powered Security: adds overhead to the packets and to the computation performed at the devices Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Power Supply (WSN) Requirements ● ● ●
Power demand assessment Energy buffer Lifetime operation
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Power Supply (WSN) Energy Sources Permanent storages: ●
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Primary batteries - energy density of around 1.2 Wh/cm³. Chemical storage / fuel cells - currently limited to hydrogen, methane or methanol; energy densities in the range of around 2 Wh/cm³. Heat storage - make use of the latent heat involved in melting or evaporation of phase change materials (PCM); melting energies of up to 0.14 Wh/cm³.
Source: Industrial Information Technology Handbook, 2nd ed., CRC Press
Richard Zurawski, Lulea, Feb. 18, 2015
Node(s) Design Issues – Power Supply (WSN) Energy Conversion Photovoltaic cells sunlight illumination density ~100mW/cm2 office lighting