Real Time Scheduling Issues in
Powertrain Controls
James B. Kolhoff
Engineering Group Manager
Front Wheel Drive Controller Team
General Motors Powertrain
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 1
Overview of Presentation
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GMPT Electronics Integration & SW - Group & Product
Scheduling Requirements and Problem
Solution
Distributed architecture
Next step
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 2
Group and Product Background
Group
GMPT is a division of General Motors, responsible for engine,
transmission, powertrain controls engineering and manufacture
Electronics Integration & Software (EI&S) is a product engineering team
responsible for the electronics and software for powertrain controls
Product
EI&S end product is an embedded microprocessor control module(s) that
controls and diagnoses engine, transmission, and vehicle functions.
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Multiple end products (ECM, TCM, PCM) with different feature content
(internal GM and external customers)
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Multiple controller and compiler suppliers
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Other vehicle module interfaces
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Development and production tool interfaces
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Controller: 32bit uc, 1Mb ROM, 150+ pins
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 3
Scheduling requirements
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Two categories of task - time synchronous, engine event
synchronous
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Time: 3.125ms, 6.25, 12.5, 25, 100 ms
Engine: crankshaft synchronous, cam synchronous
The engine event tasks cause the processing power to be
consumed in direct proportion to engine speed
Engine event synchronous tasks have harder deadlines and
higher priorities than time based tasks
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8 cylinder engine engine, event sw task execution time 1ms
600 rpm: 25ms event rate, 4% available processor thruput
7000 rpm: 2.1ms event rate, 48% available processor thruput
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 4
Task scheduling
ISRs
ENGINE POSITION TASK
PERIODIC TASK 1
PERIODIC TASK 2
BACKGROUND
OS & HWIO OVERHEAD
GMPT CODE
PRE-EMPTION TIME
EVENT
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 5
Scheduling Problems
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Most critical scheduling problem was task deadlines missed at
higher engine speeds
Basic root cause: Limited processing power
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ROM limited so we can’t do ROM tradeoffs for thruput
Fixed point math operations
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Library not optimized for performance
Requirement of ANSI-C for code portability
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Using low cost microprocessor
Low clock speed for EMC performance
Too late in program to make processor change
Not designed for performance
SW Design and Coding Standards
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Designed for reuse and readability, not performance
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 6
Solutions applied
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Re-design software for improved efficiency
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Optimize libraries to take advantage of processor specifics
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Significant work effort, reduces reuse, increases verification
requirements
Revise coding standards to maximize efficiency
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Significant work effort, potential loss of function, repeat
verification
At the expense of portability and reuse
Rework and revalidation across large number of engineers
Biggest bang for the buck - dynamic scheduling
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Can localize redesign at areas of maximum benefit
Time tasks slower than 25ms rates are insignificant to the
problem
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 7
Dynamic scheduling
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Objective: Reduce execution requirements at higher engine
speeds
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Developed engine speed zones approach
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Different function level in each zone
Simplifies coordination of scheduling change
In middle engine speed range, divide function across multiple
engine events
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Difficult to individually disable or redesign functions
Balance load across multiple cylinder events
At highest engine speeds, significantly simplify some functions
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Engine states don’t change every cylinder
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 8
Effect of Dynamic Scheduling
Engineering
Processor Utilization
110.00
100.00
90.00
Utilization
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
0
1000
2000
3000
4000
5000
6000
7000
8000
Engine Speed (RPM)
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 9
Controller System Topologies
Powertrain Control Module
Engine/Transmission Control Modules
Engine
Electrical
System
Vehicle
Electrical
System
ECM
PCM
Transmission
Electrical
System
Engine
Electrical
System
Vehicle
Electrical
System
TCM
Transmission
Electrical
System
Legend
Electrical System
Control Module
Electrical Interface
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 10
Distributed architecture
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Controller systems architecture for GMPT is changing to
separate engine controller / transmission controller
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For reasons of powertrain portfolio management
This architecture reduces the computing power needed in any
single controller
Scheduling and thruput still needed to be carefully managed
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System partitioning plays a key role
Inter-module Communications uses some of the freed up thruput
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 11
Future
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Microprocessor power has grown dramatically over the past 5
years
At the same time, costs have fallen dramatically for this power
With the microprocessors available for the projects planned,
thruput will not be the significant problem it has been in the
past
Simulation and schedule/thruput budgets are the next steps
James B. Kolhoff james.kolhoff@gm.com
© 2000 General Motors Corporation
01OC2000
Slide 12