Hệ thống nhúng - Chương 2 ppt

1 Hệ thống nhúng Thạc sĩ Lê Mạnh Hải Embedded Systems 2 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.” 3 Preflight checklist • MPLAB IDE, Integrated Development Environment • MPLAB SIM, software simulator • MPLAB C30 compiler (Student Version) 4 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: // // A loop in the pattern // 1. Select “Project→AddNewFiletoProject”, to save the fi le as: “loop.c” and have it automatically 2. added to the project source fi les list. 3. Save the project. 5 The flight “What happens when all the code in the main() function has been executed?” The device will reset, and the entire program will execute again…and again. In fact, the compiler puts a special software reset instruction right after the end of the main() function code How to keep the system alive? While loops In C there are at least three ways to code a loop; here is the fi rst—the while loop: while ( x) { // your code here } 6 Operators ( a || b) is true, ( a && b) is true ( !a) is false There are, then, a number of operators that compare numbers (integers of any kind and fl oating-point values, too) and return logic values. == 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. 7 While pattern 1. while ( 1) 2. { 3. // your code here 4. } 8 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? 9 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! 10 Problem! • 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 [...]... // TMR1 on, prescaler 1 :25 6 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 } 22 } // main loop 23 } // main 14 Logic...Software solution 1 #include 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 Delay(); 11 PORTA = 0; // turn all pin off 12 } 13 } Delay() { //Code for delay } What is code for delay 1/2s, system frequency is 32Mhz 11 Guess the system’s respond to these... plot the RA0 pin output 20 Exercises 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 2 9-4 0) 21 What is next? • CHAPTER 4: NUMBERS – List all number types? • CHAPTER 5: Interrupts (pg 53 - pg68) – What is it?... MCU clock serves as the source (Fosc /2) : TCS = 0 • The prescaler is set to the maximum value (1 :25 6): TCKPS = 11 • The input gating and synchronization functions are not required, since we use the MCU internal clock directly as the timer clock: TGATE = 0, TSYNC = 0 • We do not worry about the behavior in IDLE mode: TSIDL = 0 13 (default) 1 #include 2 #define DELAY 16000 3 main() 4 {... 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 the “View→Simulator” Logic Analyzer menu 15 16 4 Then click on the channel button, to bring up the channel-selection... 12 } 13 } Delay() { //Code for delay } What is code for delay 1/2s, system frequency is 32Mhz 11 Guess the system’s respond to these code? Software problem? Hardware solution- Timer 12 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... channel-selection dialog box 17 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 18 19 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... loop, variable, array (pg 2 9-4 0) 21 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? 22 . 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. . 1 Hệ thống nhúng Thạc sĩ Lê Mạnh Hải Embedded Systems 2 Lesson 2 : A loop in the pattern Flight plan: • Embedded-control programs need a framework, similar. pin off 12. } 13. } Delay() { //Code for delay } What is code for delay 1/2s, system frequency is 32Mhz Guess the system’s respond to these code? Software problem? 12 Hardware solution- Timer