ABS 4

1
Anti-Lock Braking System

• ABS 4
• Presenters
• Hong Jung, Binh Lai, Matthew Martin, Joe Mongiat,
  and Travis Ratcliff

2
ABS

• System Provides Anti-Lock Braking
• Wheels are prevented from locking up in hard
  braking situations
• Motivation for ABS
• Safety
• Increased control of vehicle
• Selling point
• Appeal to customer

3
Features

• Wheel Speed Sensors
• Constantly evaluate the speed of each wheel
• Information is sent to the controller upon
  request

• ABS Controller
• Calculates the deceleration rate for each wheel
• Determines when to engage the ABS for each wheel
  independently
• Sends messages to other components to activate
  them

• System Tests
• Evaluate the system upon start-up and with each
  application of the brakes

• Secondary Brake Fluid Reservoirs and Valves
• Hold fluid that is diverted from main reservoir
• Increase / Decrease interface

4
Overview of Requirements Derivation

• Rapid Prototyping - java applets
• UML Analysis - Dome
• Peer review
• Model Checking
• Xspin
• promela

5
UML Analysis
6
Use Case Diagram
7
Use case

• Problems
• Brakes in system or not
• Technician interface and actor
• Brake pressure valve actor name
• Solutions
• Brakes not in system
• Added technician actor and reset use case
• Proper naming for actor, consistent

8
Class Model
9
Class Diagram

• Problems
• Independent control of each wheel with one ABS
  controller
• Is Brake a class in model?
• How to model the pressure valve interface
• Solutions
• Methods have associated wheel
• Brake is viewed as external signal
• Simple interface, increase and decrease

10
State Diagram
11
State Diagram

• Problems
• Incorporating our concurrency ideas into model
• Brake out/in model
• Solutions
• One concurrent state machine model
• Brake is left out, viewed as a external signal

12
Sequence Diagrams
13
Power-Up/Power-Off
14
Braking
15
Model Checking
16
Promela and XSpin

• Model Analysis
• Encoded State Diagram into Promela
• Performed system simulation using XSpin

17
XSpin Simulation Results

1. Power is turned On
2. Test is run and passes
3. Brake is applied
4. Test is run and passes again
5. Brake is released
6. Brake is applied again
7. Test runs and passes
8. ABS engages and then disengages
9. Brake is released
10. Brake is applied once again
11. Test runs and fails this time
12. Fail light is turned on
13. Then technician reset is issued
14. Power is turned on again
15. Test runs and passes
16. Etc

18
Critical Properties

• Safety Properties
• If the system has a failure it shall not engage
  until fixed by a technician
• If the speed of the vehicle is below 15 MPH the
  system shall not engage
• Liveness Properties
• If wheel-lockup is imminent the ABS will
  eventually engage
• If a failure occurs within the system the
  dashboard failure light will eventually be turned
  on

19
Summary

• What is ABS?
• System Provides Anti-Lock Braking.
• Its embedded system.
• UML Analysis
• We tried to all diagrams simple and precise, but
  still making sure that we captured all
  requirements.
• Dome is good, but sometimes difficult to
  manipulate.
• Model Checking
• Verification is coming.