Hệ thống nhúng - Chương 2 ppt

Preflight checklist• MPLAB IDE, Integrated Development Environment • MPLAB SIM, software simulator • MPLAB C30 compiler Student Version... Create a new folder and name it “Loop.” name th

Hệ thống nhúng

Thạc sĩ Lê Mạnh Hải

Embedded Systems

Lesson 2 : A loop in the pattern

Flight plan:

• Embedded-control programs need a

framework, similar to the pilots’

pattern, so that the flow of code can be managed

• Loops syntax in C

• The 16-bit Timer1

• Two new MPLAB® SIM

– “Animate”

– “Logic Analyzer.”

Preflight checklist

• MPLAB IDE, Integrated Development Environment

• MPLAB SIM, software simulator

• MPLAB C30 compiler (Student Version)

The flight

1 Select “Project→Project Wizard”, to start creating a new project.

2 Select the PIC24FJ128GA010 device, and click Next.

3 Select the MPLAB C30 compiler suite and click Next.

4 Create a new folder and name it “Loop.” name the project “A Loop in the Pattern,” and clickNext.

5 There is no need to copy any source fi les from the previous lessons; click Next once more.

6 Click Finish to complete the Wizard set-up.

7 Open a new editor window.

Type the main program header:

2 added to the project source fi les list.

3 Save the project.

== the “equal-to” operator; notice it is composed of two equal signs to distinguish it from the “assignment” operator we used in the previous lesson,

!= the “NOT-equal to” operator,

> the “greater-than” operator,

>= the “greater-or-equal to” operator,

< the “less-than” operator,

<= the “less-than-or-equal to” operator

Real program

1 #include <p24fj128ga010.h>

2 main()

3 {

4 // init the control registers

5 TRISA = 0xff00; // PORTA pin 0 7 as output

6 // application main loop

7 while( 1)

8 {

9 PORTA = 0xff; // turn pin 0-7 on

10.PORTA = 0; // turn all pin off

11.}

12.}

Please guess how can we know the system is working or not?

An animated simulation

• To test the code in this example with the simulator, I

recommend you use the “Animate” mode

(Debugger→Animate) In this mode, the simulator

executes one C program line at a time, pausing for ½

second after each one to give us the time to observe the

immediate results If you add the PORTA special-function register to the Watch window, you should be able to see its value alternating rhythmicallybetween 0xff and 0x00

• In practice, if our example code was to be executed on an Explorer16 demonstration board (where the PIC24 is

running at 32 MHz), the LEDs connected to the PORTA output pins would blink too fast for our eyes to notice In fact, each LED would be turned on and off several million times each second!

• How to slow things down to a point where the LEDs would blink nicely just a couple

of times per second?

The solutions are:

• Function delay() – software solution

• Timer – hardware solution

Software solution

1 #include <p24fj128ga010.h>

2 main()

3 {

4 // init the control registers

5 TRISA = 0xff00; // PORTA pin 0 7 as output

6 // application main loop

Hardware solution- Timer

Timer1 registers

• TMR1, which contains the 16-bit counter value

• T1CON, which controls activation and the operating mode of the timer

• PR1, which can be used to produce a periodic reset of the timer

• (not required here)

• We can clear the TMR1 register to start counting from zero

• TMR1 = 0;

• Then we can initialize T1CON so that the timer will operate in a simple confi guration where:

• Timer1 is activated: TON = 1

• The main MCU clock serves as the source (Fosc/2): TCS = 0

• The prescaler is set to the maximum value (1:256): TCKPS = 11

• The input gating and synchronization functions are not required, since we use the MCU internal clock directly as the timer clock:

1 #include <p24fj128ga010.h>

2 #define DELAY 16000

3 main()

4 {

5 // init the control registers

6 TRISA = 0xff00; // PORTA pin 0 7 as output

7 T1CON = 0x8030; // TMR1 on, prescaler 1:256 Tclk/2

8 while( 1) // main application loop

9 {

10 PORTA = 0xff; // turn pin 0-7 on and wait for ¼ second

11 TMR1 = 0; // restart the count

12 while ( TMR1 < DELAY)

13 {

14 // just wait

15 }

16 PORTA = 0x00; // turn all pin off and wait for ¼ second

17 TMR1 = 0; // restart the count

18 while ( TMR1 < DELAY)

19 {

20 // just wait

21 }

Logic Analyzer

• The logic analyzer gives you a graphical and

extremely effective view of the recorded values for any number of the device output pins, but it requires a little care in the initial set-up.

• Before anything else, you should make sure that

the Tracing function of the simulator is turned on.

1 Select the “Debug→Settings” dialog box and

then choose the Osc/Trace tab.

2 In the Tracing options section, check the Trace

All box.

3 Now you can open the Analyzer window, from

4 Then click on the channel button, to bring

up the channel-selection dialog box.

5 From here, you can select the device output pins you would like to visualize.

In our case, select RA0 and click “Add =>”.

6 Click on OK to close the channel-selection dialog box.

Post-flight briefing

• MPLAB C30 compiler deals with program termination

• For the first time, we gave our little project a bit of

structure—separating the main() function in an

initialization section and an infinite loop To do so, we

learned about the while loop statements and we took the opportunity to touch briefly on the subject of logical

expressions evaluation

• We closed the lesson with a final example, where we used

a timer module for the first time and we played with the Logic Analyzer window to plot the RA0 pin output

1 Output a counter on the PORTA pins

instead of the alternating on and off

patterns.

2 Use a rotating pattern instead of

alternating on and off.

3 Readding at home CHAPTER 3: More

pattern work, more loops: Do loop, for loop, variable, array (pg 29-40)

What is next?

• CHAPTER 4: NUMBERS

– List all number types?

• CHAPTER 5: Interrupts (pg 53 - pg68)

– What is it? (what for?)

– How does it work?

– Benefits? Problems?