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Department of Computer Science University of Virginia
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CS686 - DEPENDABLE COMPUTING
ASSIGNMENT 2
DUE: FEBRUARY 12
Please type the Reading and Individual Activity parts of the assignment single spaced, 12pt type
with 1” margins, and indented paragraphs with no space between paragraphs. Be sure to include a
face page with course number and course name, assignment number, date, and your name.
For the project part, follow the project document guidelines.
The numbers after each question are the points allocated to that question.
Individual Reading
Read papers 4, 5, 6 and 7 on the class Web site. For papers 4 and 5, prepare a half-page summary.
Turn in your summaries. (20)
Individual Activity
1. A simple anti-lock braking system (ABS) for an automobile uses the following design:
Each wheel incorporates a sensor to detect wheel rotation and an actuator to release the brake
on that wheel. A computer is used to monitor wheel rotation and vehicle speed. If a wheel is
not rotating but the vehicle is moving, then the wheel is skidding and so the actuator is used to
release the brake for a very brief time, typically about 50 milliseconds. The system cycles at a
rate of about 20Hz.
The system performs numerous self checks on the hardware whenever the brakes are not being
used. If a self check fails, the system is disabled (but normal mechanical braking remains oper-
ational) and a light is illuminated to inform the driver of the system’s non-operational status. It
is not considered dangerous for the system to fail provided the failure does not occur during
braking and provided the driver’s warning light is illuminated and remains so.
Identify the degradation faults that need to be anticipated in this system. (20)
2. Identify the design fault that need to be anticipated in this system. (20)
Wheel Rotation
Sensor
Vehicle Speed
Sensor
Computer
Brake Release
Actuator
Driver’s
Warning Light
Vehicle
Wiring
