Transcript Embedded System Hardware - University of Saskatchewan

Simplified design flow
for embedded systems
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Embedded System Hardware
Embedded system hardware is frequently used in a loop
(“hardware in a loop”):
actuators
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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.
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Example: Acceleration Sensor
Courtesy & ©: S. Bütgenbach, TU Braunschweig
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Charge-coupled devices (CCD) image sensors
Based on charge transfer to next pixel cell
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CMOS image sensors
Based on standard
production process
for CMOS chips,
allows integration
with other
components.
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Example: Biometrical Sensors
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.
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Artificial eyes
© Dobelle Institute
(www.dobelle.com)
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Other sensors
• Rain sensors for wiper control
(“Sensors multiply like rabbits” [IIT automotive])
• Pressure sensors
• Proximity sensors
• Engine control sensors
• Hall effect sensors
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Discretization of time
Ve is a mapping R  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
Vx is a sequence of values or a mapping Z  R
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Discretization of values: A/D-converters
1. Flash A/D converter
Digital computers require digital form of physical values
A/D-conversion; many methods with different speeds.
Example: 1. Flash A/D converter:
Parallel comparison
with reference
voltage
Speed:
O(1)
Hardware complexity:
O(n)
with n= # of distinguished voltage
levels
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Discretization of values
2. Successive approximation
Key idea: binary search:
Set MSB='1'
if too large: reset MSB
Set MSB-1='1'
if too large: reset MSB-1
Speed:
O(ld(n))
Hardware complexity:
O(ld(n))
with n= # of distinguished
voltage levels;
slow, but high precision possible.
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Successive approximation (2)
V
1100
Vx
1011
1010
1000
V-
t
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Application areas for flash
and successive approximation converters
Effective number of bits at bandwidth
[Gielen et al., DAC 2003]
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Communication
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Communication:
Hierarchy
Inverse relation between volume and urgency quite common:
Sensor/actuator busses
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Communication
- Requirements •
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Real-time behavior
Efficient, economical (e.g. centralized power supply)
Appropriate bandwidth and communication delay
Robustness
Fault tolerance
Maintainability
Diagnosability
Security
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Basic techniques:
Electrical robustness
Single-ended vs. differential signals
ground
Voltage at input of Op-Amp positive  '1'; otherwise  '0'
Local ground
Local ground
Combined with twisted pairs; Most noise added to both wires.
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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
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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.
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Other basic techniques
• Fault tolerance:
error detecting and error correcting bus protocols
• Privacy:
encryption, virtually private networks
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Sensor/actuator busses
1. Sensor/actuator busses: Real-time behavior very
important; different techniques:
Many wires
less wires
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expensive & flexible
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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.
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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
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Field busses (3)
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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.
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Field busses (4)
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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.
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Wireless communication
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Wireless communication: Examples
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IEEE 802.11 a/b/g
UMTS
DECT
Bluetooth
UWB
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