Lab 3

Real-Time Control of a Hot Air Plant using RTOS µC/OSII

Due Date: Week of Nov. 2nd, 2010

Today's Activities

Lab 3 Presentation Special topic presentation

Rate Monotonic Scheduling (RMS) Lab 2 demos.

Lab 1 Development Environment

LabVIEW 2009 software Nios II IDE Altera Nios II Embedded Evaluation

Kit

Simple Hot Air BlowerPT 326 Process Trainer

Lab 1 Architecture

UART Write Serial Read

UART Read Serial Write

LabVIEWAltera Nios II

Plant ModelPlant Comm.

PID Controller

Operator Input

Feedback Signal

Control Signal

Input Voltage

Measured Voltage

Plant/Controller Features

Lab Requirements

Plant interface Input from plant Output to plant

PID control system Operator Interface

LCD display Operator input

Plant Interface

Input from plant Plant output voltage (from LabVIEW)

Output to plant Heater control (manipulated variable)

Communication implemented using serial communication with termination character.

Operator Interface - Inputs

Input from LCD touch screen ON/OFF signal Auto/Manual mode control Setpoint voltage (Auto Mode) Voltage input (Manual Mode)

Operator Interface - Outputs Output to LCD

Voltage/Time graph (Lab 1) + voltage setpoint

Current sampling time Voltage reference Voltage output (output to plant) Proportional gain (Kc) Integral time (Ti) Derivative Time (Td) Current time (HH:MM:SS)

Operator Display

PID Control System

m(t) = manipulated variable (output to plant) r(t) = plant setpoint c(t) = controlled variable (voltage from LabVIEW) e(t) = plant error = r(t) – c(t) Kp= Proportional gain Ti = Integral time Td = Derivative time

]/)(()(/1)([)(0

dttedTdtteTteKtm d

t

ip

PID Control Discrete Time Implementation

)]1()([)()()(

)()1()(

neneKnsKneKnm

nensns

dip

sdpd

ispi

TTKK

TTKK

/

/

Where s(n) is the sum of errors Ts = sampling time = ∆t

Implementation Requirements LabVIEW model

Two tasks: Plant Model task, communication task. Data communication between tasks using queues. Serial communication using termination character

Altera implementation Must employ at least three tasks PID controller must have a dedicated task Semaphores used for data synchronization

Note that ALL timing requirements discussed in the lab manual MUST be implemented.

Task priorities MUST be discussed and justified in your report Time delays on time critical tasks MUST be discussed and

justified in your report

Real-Time System Implementation – pg. 58-59 of lab manual

Real-Time Constraints Control system must operate with a sampling rate

of [100-500] ms ON/OFF buttons

Sampled every 2-5 seconds Auto/Manual controls

Sampled every 2-5 seconds Vinput and Vref buttons

Sampled every 1-2 seconds Clock/Time

Must execute every 1 second Operator display must be updated every 5 seconds

Task Priorities uC/OS II can manage up to 63 tasks OS has it’s own system tasks

It is recommended that you DON’T use priorities 0-5 (Highest priority = 6)

Each task must be assigned a unique priority level.

The lower the priority number the higher the priority of the task

uC/OS II will always execute the highest priority task ready to run.

Assigning Task Priorities Assigning task priorities in complex real-

time systems is a difficult job Noncritical tasks should obviously be given low

priorities Most real-time systems have a

combination of soft and hard requirements Soft RT systems: tasks are performed as quickly

as possible but they don’t have to finish by specific times

Hard RT systems: tasks must be performed correctly within the required time

Rate Monotonic Scheduling (RMS)

Priorities are assigned based on how often the tasks execute Tasks with the highest rate of execution are

given the highest priorities

Task Execution Rate (HZ)

High

Pri

ori

ty

Low

RMS Theorem– cont… RMS makes a number of assumptions

All tasks are periodic (occur at regular intervals) The CPU must always execute the highest priority

task that is ready to run Given a set of n tasks that are assigned RMS

priorities, the basic RMS theorem states that all task hard-real time deadlines are always met if the following inequality holds

i

n

i

i nT

E)12( /1

Where Ei= maximum execution time of task i Ti= execution period of task i Ei/Ti = the fraction of CPU time required to execute task i

Note: CPU use of all time-critical tasks should be less than 70%

Cont…

i

n

i

i nT

E)12( /1

Number of Tasks

1 1.000

2 0.828

3 0.779

Inf 0.693

)12( /1 nn

Deadlines and Marking Lab 3 is worth 12%. 6% for the report, and 6% for the

demo The Demo is due Nov. 2nd, 2010 in the

Lab. The Report is due Nov. 2nd, 2010 in

the Lab. A signed group evaluation sheet must

be submitted with the lab report