1. Lab. 2 Overview

2. Echo Switches to LED Lab1 Task 7
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

3. How would you handle a more complex set of embedded tests
Echo switches 1 and 2 in LED’s 1 and 2
Flash LED 3 every 2 seconds
Flash LED 4 every 1 second
Flash LED 5 every ½ second
Flash LED 6 every ¼ second
Etc
etc
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

4. If we used the “super-loop idea”
int main( ) { InitLED( ); while (1) { TaskFlashLED3( ); TaskFlashLED2( ); value = ReadSwitches( ); WriteLED(value >> 8); }
Questions
We need the processor to switch LED every 2 seconds
How do you handle the timing?
How can you get the processor to go to sleep to save battery power at other times?
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

5. Auto control of an aeroplane
Lists the tasks
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TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

6. From Pont’s book
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TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

7. Need a systematic way of programming such a system
These ideas and the following slides are based on the book by M. J. Pont – “Patterns for Time-Triggered Embedded Systems”
Down load a free copy from
The code in the book was for the 8051 processor and I have modified the code to run on Blackfin Processor
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

8. Scheduler
The idea is to make a list of all the tasks that you need to make the embedded system to work
Then you use a “scheduler” to cause the tasks to run
Pre-emptive scheduler
Co-operative Scheduler
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

9. 11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

10. ENCM Real time course
Previous classes have used Analog Devices VDK Kernel which has a pre-emptive scheduler.
Lab. 2 problems
Task to Flash LED 3 every 2 seconds
Task to Flash LED 4 every one second
Both tasks want to use same resource
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

11. Solve this problem using “lock”
#define UNLOCKED 0
#define LOCKED
Bit lock = UNLOCKED ; // Global Lock
void LED3_Task( )
while (lock == LOCKED) /* Wait for lock to be released */ ;
lock = LOCKED; // Indicate using LEDs
WriteLEDASM(LED3_ON);
lock = UNLOCKED; }
void LED4_Task( )
WriteLEDASM(LED4_ON);
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

12. Pre-emptive scheduler
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

13. Solve this problem using “lock”
#define UNLOCKED 0
#define LOCKED
Bit lock = UNLOCKED ; // Global Lock
void LED3_Task( )
while (lock == LOCKED) /* Wait for lock to be released */ ;
lock = LOCKED; // Indicate using LEDs
WriteLEDASM(LED3_ON);
lock = UNLOCKED; }
void LED4_Task( )
WriteLEDASM(LED4_ON);
Suppose LED3_Task gets switched out here and LED4_Task runs
LED4_Task thinks the resource is free to use
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TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

14. 11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

15. Scheduler code looks like this
int main( ) { Init_Scheduler( ); Add_Task(LED3_Task, 0, 2000); Add_Task(LED4_Task, 0, 1000); StartScheduler( ); while (1) { time = ReadCycleCounter( ); Dispatch_Tasks(time); } } Dispatch_Tasks(time) { if time to run LED3_Task then run LED3_Task( ); if time to run LED4_Task then run LED4_Task( ); }
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

16. Power saving code
int main( ) { Init_Scheduler( ); Add_Task(LED3_Task, 0, 2000); Add_Task(LED4_Task, 0, 1000); StartScheduler( ); -- this activates a “timer” while (1) { GoToSleepUntil_InterruptOccurs( ); time = ReadCycleCounter( ); Dispatch_Tasks(time); } } Dispatch_Tasks(time) { if time to run LED3_Task then run LED3_Task( ); if time to run LED4_Task then run LED4_Task( ); }
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

17. Lab. 2
I have found a “co-operative scheduler” that works for the 8051 using the 8051 timer interrupts. The scheduler is easy to use and the tasks are easy to write (using existing Lab. 1 code)
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

18. Task are easy to develop
void LED3_Task( ) Uses Read LED( ) and WriteLED( ) from Lab. 1 if LED3 is on turn it off if LED3 is off turn it on } void LED4_Task( ) if LED4 is on turn it off if LED4 is off turn it on
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

19. Scheduler functions SCH_Add_Task(TaskName, Delay, Period)
Thus SCH_Add_Task(Led3, 0, 1000);
Means “run” LED3 task with “no delay” the first time it is run, and then run it again after “1000 clock-ticks”. This will cause LED3 to turn on for 1000 ticks and off for 1000 ticks
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

20. Scheduler functions SCH_Add_Task(TaskName, Delay, Period)
Thus SCH_Add_Task(Led3, 0, 1000); SCH_Add_Task(Led4, 0, 2000);
Now Led3 task runs for a short time every 1000 ticks, and Led4 task runs for a short time every 2000 ticks
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

21. Other Scheduler Functions
#define MICROSECS_BETWEEN_INTERRUPTS 1000 static unsigned int tickTime = MICROSECS_BETWEEN_INTERRUPTS; SCH_Init_Scheduler(tickTime); -- Initializes the timer so that the tick time is 1 ms SCH_Start_Scheduler( ); -- Start the scheduler SCH_Dispatch_Tasks( ); -- Causes the tasks to run at the required times
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

22. Lab. 2 code looks like this
int main(int) { SCH_Init_Scheduler(tickTime); SCH_Add_Task(InitFlash_Task, NO_DELAY, RUN_ONCE); SCH_Add_Task(InitPF_Task, NO_DELAY, RUN_ONCE); SCH_Add_Task(LED3_Flash, NO_DELAY, EVERY_2000_TICKS); SCH_Add_Task(LED4_Flash, NO_DELAY, EVERY_2000_TICKS / 2); SCH_Start_Scheduler( ); while (1) { // Super loop // Wait, in low power mode, for an interrupt SCH_EnterLowPowerMode( ); // Run all the tasks in the system according to timing information SCH_Dispatch_Tasks( ); } return 0;
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

23. Lab. 2 – what’s missing
I have found a “co-operative scheduler” that works for the 8051 using the 8051 timer interrupts. We need to change this to work with the Blackfin interrupts – 5 routines needed InitializeTimer( ); StartTimer( ); StopTimer( ); EnterLowPowerMode( ); -- Enter low power mode until woken up by interrupt TimerISR( ); -- What to do when the timer interrupt occurs
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada

24. Need to know Need to understand “interrupts” on the Blackfin
Need to understand how the “core timer” and “watch dog timer” work and are programmed.
Useful to understand how the scheduler works – but not necessary unless we plan to change it
11/15/2018
TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada