embedded system hardwarewatis/courses/198420/slide005.pdfusb, firewire, isdn ethernet (stp/utp cat 5...

Embedded System Hardware

Peter MarwedelInformatik 12

Univ. DortmundGermany

- 2 - P. Marwedel, Univ. Dortmund, Informatik 12, 2006/7

Universität DortmundUniversität Dortmund

Simplified design flowfor embedded systems

Embedded System Hardware

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

actuators

Many examples of such loops

Heating Lights Engine control Power supply … Robots

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.

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

http://www.schulen.regensburg.de/hhgs/klassen/2001a/feuerwehr/kette2.jpg

Corresponding to “bucket brigade device” (German: “Eimerkettenschaltung”)

CMOS image sensors

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

Comparison CCD/CMOS sensors

Source: B. Diericks: CMOS image sensor concepts. Photonics West 2000 Short course (Web)

CMOS: low cost devices + digital SLR cameras (due to large size, …)

CCD: medium to high end non-SLR cameras

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

Show movie from www.dobelle.com (e.g. blind person driving a car)

Artificial eyes (2)

He looks hale, hearty, and healthy — except for the wires. They run from the laptops into the signal processors, then out again and across the table and up into the air, flanking his face like curtains before disappearing into holes drilled through his skull. Since his hair is dark and the wires are black, it's hard to see the actual points of entry. From a distance the wires look like long ponytails.

Other sensors

Rain sensors for wiper control Pressure sensors Proximity sensors Engine control sensors Hall effect sensors

Discretization

Discretization of time

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

Aliasing

Impossible to reconstruct fast signals after slow sampling:multiple fast signals share same sampled sequence; Example: Signal: 5.6 Hz; Sampling: 9 Hz

More info at end of chapter.[http://www.cise.ufl.edu/~prabhat/Teaching/cis6930-f04/comp1.ppt]

Discretization of values: A/D-converters1. Flash A/D converter (1)

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

Encodes input number of most significant ‘1’ as an unsigned number, e.g.“1111” -> “100”,“0111” -> “011”,“0011” -> “010”,“0001” -> “001”,“0000” -> “000”(Priority encoder).

Discretization of values: A/D-converters1. Flash A/D converter (2)

Parallel comparison with reference voltage

Speed: O(1)

Hardware complexity: O(n)

with n= # of distinguished voltage levels

Applications: e.g. in video processing

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

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

Successive approximation (2)

Application areas for flash and successive approximation converters

[Gielen et al., DAC 2003]

Effective number of bits at bandwidth

(using single bit D/A-converters;common for high quality audio equipments)[http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html]

(Pipelined flash converters)

(used in multimeters)

Quantization Noise

N = (approximated - real signal) called quantization noise.Example: quantization noise for sine wave

* [http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html]

Quantization noise for audio signal

Signal to noise for ideal n-bit converter : n * 6.02 + 1.76 [dB]

e.g. 98.1 db for 16-bit converter, ~ 160 db for 24-bit converter

signal to noise ratio (SNR )[ db ]= 20 log (effective signal voltageeffective noise voltage )

Additional noise for non-ideal converters Source: [http://www.beis.de/Elektronik/ DeltaSigma/DeltaSigma.html]

e.g.: 20 log(2)=6.02 decibels

Communication

Communication:Hierarchy

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

Safety

Basic techniques:Electrical robustness

Single-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 speed

Disadvantages: Requires negative voltages Increased number of wires and connectors

Applications: 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 bussesCarrier-sense multiple-access/collision-avoidance

(CSMA/CA)• WLAN techniques with request preceding 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

Sensor/actuator busses

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

Many wires less wires expensive & flexible

Field busses: Profibus

More powerful/expensive than sensor interfaces; mostly serial. Emphasis on transmission of small number of bytes.

Examples:

1.Process Field Bus (Profibus) Designed for factory and process automation.Focus on safety; comprehensive protocol mechanisms.Claiming 20% market share for field busses.Token passing.≦93.75 kbit/s (1200 m);1500 kbits/s (200m);12 Mbit/s (100m)Integration with Ethernet via Profinet.

[http://www.profibus.com/]

Controller area network (CAN)

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

Time-Triggered-Protocol (TTP)

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

FlexRay

4. FlexRay: developed by the FlexRay consortium(BMW, Ford, Bosch, DaimlerChrysler, …)Combination of a variant of the TTP and the Byteflight [Byteflight Consortium, 2003] protocol.Specified in SDL.

• Improved error tolerance and time-determinism

• Meets requirements with transfer rates >> CAN std.High data rate can be achieved:

– initially targeted for ~ 10Mbit/sec;

– design allows much higher data rates

• TDMA (Time Division Multiple Access) protocol:Fixed time slot with exclusive access to the bus

• Cycle subdivided into a static and a dynamic segment.

TDMA in FlexRay

Exclusive bus access enabled for short time in each case.Dynamic segment for transmission of variable length information.Fixed priorities in dynamic segment; transmissions starts at end of slot of lower priority bus node. Bandwidth used when it is actually needed.

Static segment

Channel 1

Channel 2

Channel 1

Channel 2

Communication cycle

Dynamic segment

show flexray animationfrom dortmund

Structure of Flexray networks

Bus guardian protects the system against failing processors, e.g. so-called “babbling idiots”

Other field busses

• 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.• Attempts to use standard Ethernet.

However, timing predictability remains a serious issue.

Wireless communication

Wireless communication: Examples

IEEE 802.11 a/b/g UMTS DECT Bluetooth ZigBee

Seminar "wireless communication" am LS12: 14/15.2.2006

Summary

Hardware-in-the loop Sensors (robots) Discretization

• Sample-and-hold (S/H) circuit• A/D-converters

– Flash converter– Successive approximation– Other converters– Discretization noise

Communication• Requirements• Sensor/actor-busses• Field busses

embedded system hardwarewatis/courses/198420/slide005.pdfusb, firewire, isdn ethernet (stp/utp cat 5...

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