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Chapter 11 - The C Language. BYU CS/ECEn 124The C Language2 Topics to Cover… ISR’s High Level Languages Compilers vs. Interpreters The C Language 1 st.

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Presentation on theme: "Chapter 11 - The C Language. BYU CS/ECEn 124The C Language2 Topics to Cover… ISR’s High Level Languages Compilers vs. Interpreters The C Language 1 st."— Presentation transcript:

1 Chapter 11 - The C Language

2 BYU CS/ECEn 124The C Language2 Topics to Cover… ISR’s High Level Languages Compilers vs. Interpreters The C Language 1 st C Program C Style C Preprocessor printf Function eZ430X Header Files 2 nd C Program

3 BYU CS/ECEn 124The C Language3 Interrupt Service Routines Well-written ISRs: Should be short and fast Should affect the rest of the system as little as possible Require a balance between doing very little – thereby leaving the background code with lots of processing – and doing a lot and leaving the background code with nothing to do Applications that use interrupts should: Disable interrupts as little as possible Respond to interrupts as quickly as possible Communicate w/ISR only through global variables (never through registers!!!) Interrupt Service Routine

4 BYU CS/ECEn 124The C Language4 Main Routine Interrupt Service Routines Who empties the trash? Disable Interrupts Global Variable Interrupt Service Routine Interrupt Service Routine

5 BYU CS/ECEn 124The C Language5 Levels of Abstraction Problems Algorithms Language Machine (ISA) Architecture Microarchitecture Circuits Devices Transistors Logic gates, multiplexers, memory, etc. MSP430 Architecture Machine code Assembly code High Level Languages

6 BYU CS/ECEn 124The C Language6 High Level Languages The closer a language is to your original specification, the easier the program is to write. Many, many programming languages LISP - LISt Processing PROLOG - logic programming MATLAB - matrix and vector manipulations BASIC – interpreter for small computers APL – matrix and vectors FORTRAN – formula translation COBOL – business and accounting PASCAL - procedural …. High Level Languages

7 BYU CS/ECEn 124The C Language7 High Level Languages During the part of our course, you will be introduced to fundamental high-level programming constructs: Variables Control structures Functions Arrays and Pointers Simple data structures Recursion High Level Languages

8 BYU CS/ECEn 124The C Language8 High Level Languages Allow us to use symbolic names for values Programmer simply assigns each value a name Allow us to ignore many memory details, the compiler takes care of … register usage variable allocation loads and stores from memory callee/caller protocol stack management for subroutine calls High Level Languages

9 BYU CS/ECEn 124The C Language9 High Level Languages Provide abstraction of underlying hardware Hide low level details (ISA) from programmer Uniform interface (not tied to ISA) to program Portable software (works on different ISAs) The compiler generates the machine code High Level Languages if ((a >= '0') && (a <= '9')) { sum = sum * 10; sum = sum + (a - '0'); } else... if ((a >= '0') && (a <= '9')) { sum = sum * 10; sum = sum + (a - '0'); } else...

10 BYU CS/ECEn 124The C Language10 High Level Languages Provide expressiveness Human-friendly orientation Express complex tasks with smaller amount of code English-like and human readable if-then-else… while… for... switch… High Level Languages if(isCloudy) get(umbrella); else get(sunglasses); if(isCloudy) get(umbrella); else get(sunglasses);

11 BYU CS/ECEn 124The C Language11 High Level Languages Enhance code readability Can read like a novel… if written with readability in mind Readability.. is very important life cycle costs are more important than initial programming costs Easier to debug Easier to maintain High Level Languages main() { readInput(); checkForErrors(); doCalculation(); writeOutput(); } main() { readInput(); checkForErrors(); doCalculation(); writeOutput(); }

12 BYU CS/ECEn 124The C Language12 High Level Languages Provide safeguards against bugs Rules can lead to well-formed programs structured programming (no GOTO statements) Compilers can generate checks array bounds checking data type checking Many languages provide explicit support for assertions something that should be true - if it isn’t, then error High Level Languages assert(accountBalance >= 0);

13 BYU CS/ECEn 124The C Language13 Compilation vs. Interpretation Interpretation: An interpreter reads the program and performs the operations in the program The program does not execute directly, but is executed by the interpreter. Compilation: A compiler translates the program into a machine language program called an executable image. The executable image of the program directly executes on the hardware. The interpreter and compiler are themselves programs Compilers vs Interpreters

14 BYU CS/ECEn 124The C Language14 Interpretation Algorithm High-Level Language Program c = a + b; by hand Interpreter read & execute program text Compilers vs Interpreters

15 BYU CS/ECEn 124The C Language15 Interpretation Program code is interpreted at runtime lines of code are read in interpreter determines what they represent requested function is performed interpret() { while(1) // do forever { readInputLine(); if(line[0..3] == "mult") doMultiply(); else if(line[0..2] == "add") doAdd(); else... } interpret() { while(1) // do forever { readInputLine(); if(line[0..3] == "mult") doMultiply(); else if(line[0..2] == "add") doAdd(); else... } Interpretation is common: + LISP + BASIC + Perl + Java + Matlab + LC-2 simulator + UNIX shell + MS-DOS command line Interpretation can be slow... Compilers vs Interpreters

16 BYU CS/ECEn 124The C Language16 Compilation Algorithm C-language program c = a + b; by hand Machine language programs assembler Assembly language program ADD r0,r1,r2 compiler to machine for execution The assembly language stage is often skipped… Compiler often directly generates machine code. Compilers vs Interpreters

17 BYU CS/ECEn 124The C Language17 Compilation Compilers convert high-level code to machine code compile once, execute many times resulting machine code is optimized may include intermediate step (assembly) slower translation, but higher performance when executed Is an assembler considered a compiler? assemblers do convert higher level code to machine code, but… they are usually in a class by themselves Compilers vs Interpreters

18 BYU CS/ECEn 124The C Language18 The C Programming Language Developed 1972 by Dennis Ritchie at Bell Labs C first developed for use in writing compilers and operating systems (UNIX) A low-level high-level language Many variants of C 1989, the American National Standards Institute standardized C (ANSI C, most commonly used C) “The C Programming Language” by Kernighan and Ritchie is the C “Bible” C is predecessor to most of today’s procedural languages such as C++ and Java. The C Language

19 BYU CS/ECEn 124The C Language19 Compiling a C Program The C Language Object Code Assembler Code C/C++ Code Machine Code

20 BYU CS/ECEn 124The C Language20 Compiling a C Program C Source Code C Preprocessor Library & Object Files Executable Image C Compiler The C Language Preprocessed source code Source Code Analysis 1 st Pass Symbol Table Code Generation 2 nd Pass Linker Object module

21 BYU CS/ECEn 124The C Language21 A First Program //************************************ // blinky.c: Software Toggle P1.0 //************************************ #include "msp430x22x4.h" void main(void) { int i = 0; WDTCTL = WDTPW + WDTHOLD; // stop WD P1DIR |= 0x01; // P1.0 output for (;;) // loop { P1OUT ^= 0x01; // toggle P1.0 while (--i); // delay } Tells compiler to use all the definitions found in the msp430x22x4.h library. A.h file is called a header file and contains definitions and declarations. All programs must have a main() routine. This one takes no arguments (parameters). Set P1.0 as output Loop forever Toggle P1.0 Delay 65,536 1 st C Program Stop WD w/Password

22 BYU CS/ECEn 124The C Language22 Comments Use lots of comments /* This is a comment */ // This is a single line comment Comment each procedure telling: /* * * ProcedureName – what it does * * Parameters: * * Param1 – what param1 is * * Param2 – what param2 is * * Returns: * * What is returned, if anything * * */ Use lots of white space (blank lines) C Style

23 BYU CS/ECEn 124The C Language23 Indenting Style Each new scope is indented 2 spaces from previous Put { on end of previous line, or start of next line Line matching } up below Style is something of a personal matter. Everyone has their own opinions… What is presented here is similar to that in common use and a good place to start... if(a < b) { b = a; a = 0; } else { a = b; b = 0; } if(a < b) { b = a; a = 0; } else { a = b; b = 0; } Style 1 if(a < b) { b = a; a = 0; } else { a = b; b = 0; } if(a < b) { b = a; a = 0; } else { a = b; b = 0; } Style 2 C Style

24 BYU CS/ECEn 124The C Language24 More On Indenting Style For very long clauses, you may want to add a comment to show what the brace is for: if(a < b) { /* Lots of code here... */ } // end if(a < b) else { /* Lots of code here... */ } // end else if(a < b) { /* Lots of code here... */ } // end if(a < b) else { /* Lots of code here... */ } // end else C Style

25 BYU CS/ECEn 124The C Language25 The C Preprocessor #define symbol code The preprocessor replaces symbol with code everywhere it appears in the program below #define NUMBER_OF_MONKEYS 259 #define MAX_LENGTH 80 #define PI #include filename.h The preprocessor replaces the #include directive itself with the contents of header file filename.h #include /* a system header file */ #include "myheader.h" /* a user header file */ Preprocessor command are not terminated with ‘;’ C Preprocessor

26 BYU CS/ECEn 124The C Language26 eZ430X System Functions eZ430X.h and eZ430X.c int eZ430X_init (int clock_speed);// init system void ERROR2 (int error);// fatal error Setting system clock eZ430X Header Files #include "msp430x22x4.h" #include "eZ430X.h" #define myClock CALDCO_8MHZ #define CLOCK // SMCLK = ~8 mhz void main(void) { eZ430X_init(myClock); // init board ERROR2(5); }

27 BYU CS/ECEn 124The C Language27 C I/O I/O facilities are not part of the C language itself Nonetheless, programs that do not interact with their environment are useless The ANSI standard defines a precise set of I/O library functions for portability Programs that confine their system interactions to facilities provided by the standard library can be moved from one system to another without change. The properties of the C I/O library functions are specified in header files (C standard library) "eZ430X.h", "lcd.h" (eZ430X) eZ430X Header Files

28 BYU CS/ECEn 124The C Language28 Output in C printf( format_string, parameters ) printf("\nHello World"); printf("\n%d plus %d is %d", x, y, x+y); printf("\nIn hex it is %x", x+y); printf("\nHello, I am %s. ", myname); printf("\nIn ascii, 65 is %c. ", 65); Output: Hello world 5 plus 6 is 11 In hex it is b Hello, I am Bambi. In ascii, 65 is A. printf Function String literal Decimal Integer Hex Integer String Character Newline

29 BYU CS/ECEn 124The C Language29 LCD lcd.c Prototypes int lcd_init (void); void lcd_volume(int volume); void lcd_backlight (int backlight); int lcd_display(int mode); void lcd_clear(int value); void lcd_image(const unsigned char* image, int column, int page); void lcd_blank(int column, int page, int width, int height); void lcd_cursor (int column, int page); char lcd_putchar(char c); void lcd_printf (char* fmt,...); printf Function

30 BYU CS/ECEn 124The C Language30 LCD LCD x 160 x 4 pixels display Y (0-99)   Page 10  Page 9  Page 8  Page 7  Page 6  Page 5  Page 4  Page 3  Page 2  Page 1  Page 0  Page 12  Page 11 printf Function Hello World! // 5 x 8 pixel Characters lcd_cursor(40, 5); lcd_printf("Hello World!"); X (0-159) 

31 BYU CS/ECEn 124The C Language31 // File: ftoc.c // Date: 02/15/2010 // Author: Joe Coder // Description: Output a table of Fahrenheit and Celsius temperatures. #include "msp430x22x4.h" #include "eZ430X.h" #include "lcd.h" #define LOW 0 // Starting temperature #define HIGH 100 // Ending temperature #define STEP 10// increment int main(void) { int fahrenheit; // Temperature in fahrenheit float celsius; // Temperature in celsius WDTCTL = WDTPW + WDTHOLD;// Stop WDT eZ430X_init(CALDCO_1MHZ);// init board lcd_init(); // Loop through all the temperatures, printing the table for(fahrenheit = LOW; fahrenheit <= HIGH; fahrenheit += STEP) { celsius = (fahrenheit - 32) / 1.8; printf("\nf=%d, c=%.1f", fahrenheit, celsius); } Use #define’s for magic numbers A Second Program 1 digit to the right of the decimal point. #include the lcd functions Use meaningful names for variables 2 nd C Program

32 BYU CS/ECEn 124The C Language32

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