Lab. 2 Overview Move the tasks you developed in Lab. 1 into the more controllable TTCOS operating system Manual control of RC car

Lab. 2 Overview

Move the tasks you developed in Lab. 1 into the more controllable TTCOS operating system

Manual control of RC car

Lab 1 Task 4AUncontrolled switch copy

04/20/23TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada 2 / 28

How would you handle a more complex set of embedded tests

Echo switches 1 and 2 in LED’s 1 and 2Flash LED 3 every 2 secondsFlash LED 5 every ½ secondFlash LED 6 every ¼ secondDo something else for 4 seconds, then

something else for 12 and then something else for 5 – Assignment 1

Etc


If we used the “super-loop idea”

int main( ) {

InitLED( );

while (1) {

if CorrectTIme(time1) then TaskFlashLED3( );

I if CorrectTIme(time 2) then TaskFlashLED3( ); value = ReadSwitches( ); WriteLED(value >> 8);

}

Actual code on next slide


QUESTONS TO ASNWER

1.We need the processor to switch LED every 2 seconds

2.How do you handle the timing?

3.How can you get the processor to go to sleep to save battery power at other times?

Super loop – Lab 1 Task 4B


From Pont’s bookControl of an aeroplane


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

www.tte-systems.com/downloads/pttes_0408a.pdf

The code in the book was for the 8051 processor and I have modified the code to run on Blackfin Processor


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 -- discussed FridayTasks run as random events

Co-operative Scheduler -- discussed FridayTasks run at predictable intervals


Lab. 2 Task 2 – Download TTCOS and validate the install

Check the web pages for install detailsTTCOS511.h file

all the prototypes for the TTCOS functionsTTCOS511.dlb

the TTCOS library for the BlackfinExample_TTCOSmain.c

Use this as a template for all TTCOS programs in Labs, assignment and quizzes and exams)


Example_TTCOS main.cpp


The only lines of codethat ever change

FOR OTHER LAB 2 partsreplace these lines

The total code for Lab. 2 Task 2


First task – name -- Task_SayGreetingRuns with no delay

Runs only once

Second task – name -- Task_SayHiOccasionallyRuns with no delay

Runs every 5 seconds, and then allows processor to sleep

Lab. 2 – Task 3: Reuse Lab. 1 Functions within TTCOS


Step 1 in processRecognize the tasks that are needed

3 RUN_ONCE2 PERIODIC

Step 1 – Add TTCOS task to initialize system

One TTCOS task activates many others


So this is the code we need to replace – Lab 1 Task 4B


Lets add the flashing LED tasks

For predictability – each task runs in its own time slot 1 / 48000 apart


Uncoupling actions -- Use two task to do copy of switches to LEDs

Later will have a task that copies switch values to RC car


Final task is more difficult

In Lab 1 Task 4B - Controlled echo (copy) of switches to LED we simply had DO CheckSwitch4PressedAndReleased( ) stop the loop.


We can't stop the operating system -- so we much use a KILL task based on the old CheckSwitch4 task


New switch 4 task – calls a kill task

Possible error messages from ‘task race’


Halloween – so we bring the killed tasks back to life


Lab 2 Task 4 -- Make PF lines INPUT and OUPUT at same time


ChristineTask -- Step 1


Christine Task – step 2

Control the wheels to turn the car left and right

Use AND and OR instructions, otherwise you will destroy the input switch values


ChristineTask( ) – Step 3

Run these task every 1/ 4 second – no more often – the car will not respond any faster


Major milestone (B- on Lab)


Task 5 -- totally automated


What does code look like on pre-emptive scheduler?

int main( ) {Setup LED, SwitchesSet Up interrupts( ) and start them

while (1 ) { // Lab. 1 Task 7 Read Switches and Write to LED;

}

}

Timer1_ISR( ) { // Only happens when Timer1 alarm rings

Flash LED 3( );}

Timer2_ISR( ) { // Only happens when Timer1 alarm rings

Flash LED 4( );}


Problem is “what happens ifboth alarms ring at same time

(with larger ISR code)

InterruptServiceRoutine

“Subroutine activated by hardware”not by “code” -- unpredictable

ENCM Real time course Pre-emptive scheduler

Lab. 2 problemsTask to Flash LED 3 every 2 secondsTask to Flash LED 4 every one second

Both tasks want to use same resourceWhat happens if one task starts to save

something and gets interrupted?


We think we can solve this problem using “locks” and “semaphores”

#define UNLOCKED 0

#define LOCKED 1

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( )




lock = UNLOCKED;

}04/20/23

TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada 29 / 28

Solve this problem using “lock”#define UNLOCKED 0

#define LOCKED 1

Bit lock = UNLOCKED ; // Global Lock

void LED3_Task( )




lock = UNLOCKED;

}

void LED4_Task( )




lock = UNLOCKED;

}04/20/23

TDD-Core Timer Library, Copyright M. Smith, ECE, University of Calgary, Canada 30 / 28

Suppose LED3_Task

gets switched out hereand LED4_Task runs

LED4_Task thinks the resource

is free to use


Need to know in future lectures

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


Documents

Lab. 2 Overview Move the tasks you developed in Lab. 1 into the more controllable TTCOS operating system Manual control of RC car