Advanced Embedded Systems Design

1
Advanced Embedded Systems Design

• Lecture 3 Time triggered tasking and controlling
  timing and
• BAE 5030 - 003
• Fall 2004
• Instructor Marvin Stone
• Biosystems and Agricultural Engineering
• Oklahoma State University

2
Goals for Class Today

• Questions over reading
• Priority inversion (Carol Jones)
• Time triggered tasking and use of hardware delay
• Keil Compiler
• ISRs
• Profiling
• Set assignment

3
Delay Hardware Timer/Counter peripherals

• Typically provide
• Counter that can be read from the microcontroller
• 8 to 32 bits wide
• Pre-loaded from microcontroller or auto-reload
• Driven by
• Microcontroller clock (Timer)
• External source (Counter)
• Interrupts on
• Overflow
• Input transition (Pulse width measurement)
• Edge and level
• Enable
• Timer run
• Interrupt

4
Additional Timer/Counter peripheral features

• Functional tasks addressed by counter / timer
  devices
• Time triggering interrupt or polled timing
• Pulse counting External input, read at period
  of interest, may provide gated counting
• Duty cycle measurement pulse count high and low
• Pulse width measurement
• PWM generation
• Advanced features
• PWM facilities duty cycle / period control,
  write on the fly
• Auto-reload after timeout
• Match and latch - accumulate time or count then
  latch another timer
• Stepper motor control

5
Example 8051 Timer Mode 0,1

• 8051 timer 0,1 in Mode 0
• 8051 timer 0,1 in Mode 1

6
Example 8051 Timer Mode 0,1

• 8051 timer 0,1 in Mode 2
• Mode 3 TL0 is an 8-bit Timer/Counter. TH0 is an
  8-bit Timer using Timer 1s TR0 and TF0 bits.
  Mode 3 for Timer 1 halts timer 1
• Timer 2 (3) Generally has a 16 bit auto-reload
  mode

7
Use of hardware to control timing

• General structure of a hardware timed loop
• For a manually read timer, provision should be
  made to detect timer overflow
• If task is too long, a timer cycle may be missed
• Review code for hardware delay (Chapter 11 code)
• Review code for ISR on web
• Coding rules
• Timer setup
• ISR
• Multi-Tasking

8
Assignment

• Recode the time tasking example to
• 1) Print Hello World as the task
• 2) Lengthen the task period to 10 ms.
• Read Pont, Chapters 13,14
• Tutorial 30 min
• Explain a pre-emptive two three task scheduler