Embedded OS
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Creating an Embedded Operating System 2 Super Loop Limitations The super loop cannot be used to periodically execute a function at fixed intervals unless: We know the precise execution time for the function The execution time is fixed and never varies 3 Sample Situations with Periodic Timing Needs A music sample must be converted every 20 ms. The current speed of the vehicle must be measured at 0.5 second intervals. The display must be refreshed 40 times every second. The calculated new throttle setting must be applied every 0.5 seconds. A time-frequency transform must be performed 20 times every second. The engine vibration data must be sampled 1000 times per second. The frequency-domain data must be classified 20 times every second. The keypad must be scanned every 200 ms. The master (control) node must communicate with all other nodes (sensor nodes and sounder nodes) once per second. The new throttle setting must be calculated every 0.5 seconds. The sensors must be sampled once per second.
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This document is lecture note about embedded operating system
Transcript of Embedded OS
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Creating an Embedded Operating System
2
Super Loop Limitations
| The super loop cannot be used to periodically execute a function at fixed intervals unless:zWe know the precise execution time
for the functionz The execution time is fixed and never
varies
3
Sample Situations with Periodic Timing Needs
| A music sample must be converted every 20 ms.| The current speed of the vehicle must be measured at 0.5 second
intervals.| The display must be refreshed 40 times every second.| The calculated new throttle setting must be applied every 0.5
seconds.| A time-frequency transform must be performed 20 times every
second.| The engine vibration data must be sampled 1000 times per second.| The frequency-domain data must be classified 20 times every
second.| The keypad must be scanned every 200 ms.| The master (control) node must communicate with all other nodes
(sensor nodes and sounder nodes) once per second.| The new throttle setting must be calculated every 0.5 seconds.| The sensors must be sampled once per second.
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4A Simple Embedded OS
| Use a timer in conjunction with an interrupt to periodically run an interrupt service routine
| The interrupt signal is often referred to as the system tick
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Modified Super Loop
void main(void){
Timer_2_Init(); // Set up Timer 2EA = 1; // Globally enable interruptswhile(1); // An empty Super Loop
}
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Interrupt Sources
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7Automatic Timer Reloads
| Timers 0 and 1 can be automatically reloaded in 8-bit mode
| Timer 2 is automatically reloaded every time it overflows
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Timer-driven vs. Event-driven
| In a timer-driven system, the system relies on a fixed system tick to run tasks
| In an event-driven system, the systems depends on external interrupts to run tasks
Which is more reliable? Why?
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Co-operative vs. pre-emptive Scheduling| A co-operative schedule lets tasks run
to completion before switching to another task
| A pre-emptive scheduler runs multiple tasks in a round-robin fashion
Which is more reliable? Why?
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Design Considerations
| It is important that the total time of all tasks not exceed the system tick
| It is prudent to not use any other interrupts in conjunction with the timer interrupt in order to avoid conflict between interrupt service routines
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Measuring Flow
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Embedded vs. Real-Time OS
