01oc2000 slide 1 © 2000 general motors corporation james b. kolhoff [email protected] real time...
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01OC2000 Slide 1© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Real Time Scheduling Issues in Powertrain Controls
James B. KolhoffEngineering Group Manager
Front Wheel Drive Controller TeamGeneral Motors Powertrain
01OC2000 Slide 2© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Overview of Presentation
GMPT Electronics Integration & SW - Group & Product Scheduling Requirements and Problem Solution Distributed architecture Next step
01OC2000 Slide 3© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Group and Product Background
GroupGMPT 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
ProductEI&S end product is an embedded microprocessor control module(s) that
controls and diagnoses engine, transmission, and vehicle functions. Multiple end products (ECM, TCM, PCM) with different feature content
(internal GM and external customers) Multiple controller and compiler suppliers Other vehicle module interfaces Development and production tool interfaces Controller: 32bit uc, 1Mb ROM, 150+ pins
01OC2000 Slide 4© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Scheduling requirements
Two categories of task - time synchronous, engine event synchronous
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
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
01OC2000 Slide 5© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Task scheduling
ISRs
ENGINE POSITION TASK
PERIODIC TASK 1
PERIODIC TASK 2
BACKGROUND
OS & HWIO OVERHEADGMPT CODEPRE-EMPTION TIME
EVENT
01OC2000 Slide 6© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Scheduling Problems
Most critical scheduling problem was task deadlines missed at higher engine speeds
Basic root cause: Limited processing power Using low cost microprocessor Low clock speed for EMC performance Too late in program to make processor change
ROM limited so we can’t do ROM tradeoffs for thruput Fixed point math operations
Library not optimized for performance Requirement of ANSI-C for code portability
Not designed for performance SW Design and Coding Standards
Designed for reuse and readability, not performance
01OC2000 Slide 7© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Solutions applied
Re-design software for improved efficiency Significant work effort, potential loss of function, repeat verification
Optimize libraries to take advantage of processor specifics Significant work effort, reduces reuse, increases verification
requirements Revise coding standards to maximize efficiency
At the expense of portability and reuse Rework and revalidation across large number of engineers
Biggest bang for the buck - dynamic scheduling Can localize redesign at areas of maximum benefit Time tasks slower than 25ms rates are insignificant to the problem
01OC2000 Slide 8© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Dynamic scheduling
Objective: Reduce execution requirements at higher engine speeds
Difficult to individually disable or redesign functions Developed engine speed zones approach
Different function level in each zone Simplifies coordination of scheduling change
In middle engine speed range, divide function across multiple engine events
Balance load across multiple cylinder events At highest engine speeds, significantly simplify some functions
Engine states don’t change every cylinder
01OC2000 Slide 9© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Effect of Dynamic Scheduling
Processor Utilization
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Engine Speed (RPM)
Uti
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01OC2000 Slide 10© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Controller System Topologies
PCMVehicle
ElectricalSystem
EngineElectricalSystem
TransmissionElectricalSystem
ECM
TCM
VehicleElectricalSystem
EngineElectricalSystem
TransmissionElectricalSystem
Legend
Electrical System
Control Module
Electrical Interface
Powertrain Control Module Engine/Transmission Control Modules
01OC2000 Slide 11© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Distributed architecture
Controller systems architecture for GMPT is changing to separate engine controller / transmission controller
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
System partitioning plays a key role Inter-module Communications uses some of the freed up thruput
01OC2000 Slide 12© 2000 General Motors CorporationJames B. Kolhoff [email protected]
Future
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