- 1 - Embedded Systems – sensors-comm Simplified design flow for embedded systems

- 1 -Embedded Systems – sensors-comm

Simplified design flowfor embedded systems


Embedded System Hardware

Embedded system hardware is frequently used in a loop(“hardware in a loop”):

Embedded system hardware is frequently used in a loop(“hardware in a loop”):

actuators


Sensors

Processing of physical data starts with capturing this data.

Sensors can be designed for virtually every physical and

chemical quantity• including weight, velocity, acceleration, electrical current,

voltage, temperatures etc.• chemical compounds.

Many physical effects used for constructing sensors.

Examples:• law of induction (generation of voltages in an electric field),• light-electric effects.

Huge amount of sensors designed in recent years.

Processing of physical data starts with capturing this data.

Sensors can be designed for virtually every physical and

chemical quantity• including weight, velocity, acceleration, electrical current,

voltage, temperatures etc.• chemical compounds.

Many physical effects used for constructing sensors.

Examples:• law of induction (generation of voltages in an electric field),• light-electric effects.

Huge amount of sensors designed in recent years.


Example: Acceleration Sensor

Courtesy & ©: S. Bütgenbach, TU Braunschweig


Charge-coupled devices (CCD) image sensors

Based on charge transfer to next pixel cellBased on charge transfer to next pixel cell


CMOS image sensors

Based on standard production process for CMOS chips, allows integration with other components.

Based on standard production process for CMOS chips, allows integration with other components.


Example: Biometrical Sensors

Example: Fingerprint sensor (© Siemens, VDE):Example: Fingerprint sensor (© Siemens, VDE):

Matrix of 256 x 256 elem.Voltage ~ distance. Resistance also computed. No fooling by photos and wax copies.Carbon dust?

Integrated into ID mouse.


Artificial eyes

© Dobelle Institute(www.dobelle.com)


Other sensors

• Rain sensors for wiper control(“Sensors multiply like rabbits” [IIT automotive])

• Pressure sensors• Proximity sensors• Engine control sensors• Hall effect sensors

• Rain sensors for wiper control(“Sensors multiply like rabbits” [IIT automotive])

• Pressure sensors• Proximity sensors• Engine control sensors• Hall effect sensors


Discretization of time

Vx is a sequence of values or a mapping Z R Vx is a sequence of values or a mapping Z R

In this course: restriction to digital information processing; Known digital computers can only process discrete time series Discrete time; sample and hold-devices.

Ideally: width of clock pulse -> 0

In this course: restriction to digital information processing; Known digital computers can only process discrete time series Discrete time; sample and hold-devices.

Ideally: width of clock pulse -> 0

Ve is a mapping R RVe is a mapping R R


Discretization of values: A/D-converters1. Flash A/D converter

Parallel comparison with reference voltage

Speed: O(1)

Hardware complexity: O(n)

with n= # of distin-guished voltage levels

Parallel comparison with reference voltage

Speed: O(1)

Hardware complexity: O(n)

with n= # of distin-guished voltage levels

Digital computers require digital form of physical valuesA/D-conversion; many methods with different speeds.Example: 1. Flash A/D converter:

Digital computers require digital form of physical valuesA/D-conversion; many methods with different speeds.Example: 1. Flash A/D converter:


Discretization of values2. Successive approximation

Key idea: binary search:Set MSB='1'if too large: reset MSBSet MSB-1='1'if too large: reset MSB-1

Key idea: binary search:Set MSB='1'if too large: reset MSBSet MSB-1='1'if too large: reset MSB-1

Speed: O(ld(n))Hardware complexity: O(ld(n))with n= # of distinguishedvoltage levels;slow, but high precision possible.

Speed: O(ld(n))Hardware complexity: O(ld(n))with n= # of distinguishedvoltage levels;slow, but high precision possible.


Successive approximation (2)

1100

1000

1010

1011

t

V

Vx

V-


Application areas for flash and successive approximation converters

[Gielen et al., DAC 2003]

Effective number of bits at bandwidth


Communication


Communication:Hierarchy

Inverse relation between volume and urgency quite common: Inverse relation between volume and urgency quite common:

Sensor/actuator busses


Communication- Requirements -

• Real-time behavior• Efficient, economical (e.g. centralized power supply)• Appropriate bandwidth and communication delay• Robustness• Fault tolerance• Maintainability• Diagnosability• Security

• Real-time behavior• Efficient, economical (e.g. centralized power supply)• Appropriate bandwidth and communication delay• Robustness• Fault tolerance• Maintainability• Diagnosability• Security


Basic techniques:Electrical robustness

Single-ended vs. differential signalsSingle-ended vs. differential signals

Voltage at input of Op-Amp positive '1'; otherwise '0'

Combined with twisted pairs; Most noise added to both wires.

ground

Local groundLocal ground


Evaluation

Advantages:• Subtraction removes most of the noise• Changes of voltage levels have no effect• Reduced importance of ground wiring• Higher speedDisadvantages:• Requires negative voltages• Increased number of wires and connectorsApplications:• USB, FireWire, ISDN• Ethernet (STP/UTP CAT 5 cables)• differential SCSI• High-quality analog audio signals

Advantages:• Subtraction removes most of the noise• Changes of voltage levels have no effect• Reduced importance of ground wiring• Higher speedDisadvantages:• Requires negative voltages• Increased number of wires and connectorsApplications:• USB, FireWire, ISDN• Ethernet (STP/UTP CAT 5 cables)• differential SCSI• High-quality analog audio signals


Real-time behavior

Carrier-sense multiple-access/collision-detection (CSMA/CD, Standard Ethernet) no guaranteed response time.

Alternatives:• token rings, token busses• Carrier-sense multiple-access/collision-avoidance (CSMA/CA)

– WLAN techniques with request preceeding transmission– Each partner gets an ID (priority). After each bus transfer,

all partners try setting their ID on the bus; partners detecting higher ID disconnect themselves from the bus. Highest priority partner gets guaranteed response time; others only if they are given a chance.

Carrier-sense multiple-access/collision-detection (CSMA/CD, Standard Ethernet) no guaranteed response time.

Alternatives:• token rings, token busses• Carrier-sense multiple-access/collision-avoidance (CSMA/CA)

– WLAN techniques with request preceeding transmission– Each partner gets an ID (priority). After each bus transfer,

all partners try setting their ID on the bus; partners detecting higher ID disconnect themselves from the bus. Highest priority partner gets guaranteed response time; others only if they are given a chance.


Other basic techniques

• Fault tolerance:error detecting and error correcting bus protocols

• Privacy:encryption, virtually private networks

• Fault tolerance:error detecting and error correcting bus protocols

• Privacy:encryption, virtually private networks


Sensor/actuator busses

1. Sensor/actuator busses: Real-time behavior very important; different techniques:

1. Sensor/actuator busses: Real-time behavior very important; different techniques:

Many wires less wires expensive & flexible


Field busses

More powerful/expensive than sensor interfaces; serial busses preferred. Examples:

1. Process Field Bus (Profibus) (see //www.profibus.com)Token passing;9.6 kbit/s (1200 m) to 500 kbits/s (200m);to slow to be used for hard time constraints.

More powerful/expensive than sensor interfaces; serial busses preferred. Examples:

1. Process Field Bus (Profibus) (see //www.profibus.com)Token passing;9.6 kbit/s (1200 m) to 500 kbits/s (200m);to slow to be used for hard time constraints.


Field busses (2)

Controller area network (CAN)• Designed by Bosch and Intel in 1981;• used in cars and other equipment;• differential signaling with twisted pairs,• arbitration using CSMA/CA,• throughput between 10kbit/s and 1 Mbit/s,• low and high-priority signals,• maximum latency of 134 µs for high priority signals,• coding of signals similar to that of serial (RS-232) lines of

PCs, with modifications for differential signaling.• See //www.can.bosch.com

Controller area network (CAN)• Designed by Bosch and Intel in 1981;• used in cars and other equipment;• differential signaling with twisted pairs,• arbitration using CSMA/CA,• throughput between 10kbit/s and 1 Mbit/s,• low and high-priority signals,• maximum latency of 134 µs for high priority signals,• coding of signals similar to that of serial (RS-232) lines of

PCs, with modifications for differential signaling.• See //www.can.bosch.com


Field busses (3)

• The Time-Triggered-Protocol (TTP) [Kopetz et al.]• for fault-tolerant safety systems like airbags in cars.

• FlexRay: TDMA (Time Division Multiple Access) protocol, developed by the FlexRay consortium (BMW, Ford, Bosch, DaimlerChrysler, General Motors, Motorola, Philips).Combination of a variant of the TTP and the byteflight [Byteflight Consortium, 2003] protocol.- Designed to meet key automotive requirements- Complements the major in-vehicle networking standards- A high data rate can be achieved: initially targeted for a data rate of approximately 10Mbit/sec; however, the design of the protocol allows much higher data rates to be achieved.

• The Time-Triggered-Protocol (TTP) [Kopetz et al.]• for fault-tolerant safety systems like airbags in cars.

• FlexRay: TDMA (Time Division Multiple Access) protocol, developed by the FlexRay consortium (BMW, Ford, Bosch, DaimlerChrysler, General Motors, Motorola, Philips).Combination of a variant of the TTP and the byteflight [Byteflight Consortium, 2003] protocol.- Designed to meet key automotive requirements- Complements the major in-vehicle networking standards- A high data rate can be achieved: initially targeted for a data rate of approximately 10Mbit/sec; however, the design of the protocol allows much higher data rates to be achieved.


Field busses (4)

• MAP:MAP is a bus designed for car factories.• EIB:The European Installation Bus (EIB) is a bus designed

for smart homes.European Installation Bus (EIB)Designed for smart buildings; CSMA/CA; low data rate.

• IEEE 488: Designed for laboratory equipment.

• MAP:MAP is a bus designed for car factories.• EIB:The European Installation Bus (EIB) is a bus designed

for smart homes.European Installation Bus (EIB)Designed for smart buildings; CSMA/CA; low data rate.

• IEEE 488: Designed for laboratory equipment.


Wireless communication


Wireless communication: Examples

• IEEE 802.11 a/b/g• UMTS• DECT• Bluetooth• UWB

• IEEE 802.11 a/b/g• UMTS• DECT• Bluetooth• UWB

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- 1 - Embedded Systems – sensors-comm Simplified design flow for embedded systems