Programming in C Language

Transcription

1 Brno University of Technology Programming in C Language Microprocessor Techniques and Embedded Systems Lecture 5 Dr. Tomas Fryza Ver

2 Contents Microcontrollers Programming in C Language Application Compilation Programming in C Language Combination of Assembly and C Language Source Code Example for ATmega16 (C Language)

4 C language Figure: Dennis MacAlistair Ritchie ( ) D.M.Ritchie, Brian Kernighan. The C Programming Language First edition of The C Programming Language by Brian Kernighan and Dennis Ritchie (1978, called K&R C) defined the C language, but not the C library. C89 ANSI (American National Standards Institute) developed a new standard in 1989 (called ANSI C). This new standard defines both the language and a standard C library. C90 The International Organization for Standardization adopted a C standard (ISO C) in ISO C and ANSI C are essentially the same standard. The final version of the ANSI/ISO standard is often referred to as C89 or C90. C99 In 1994, work began on revising the standard, an effort that resulted in the C99 standard. C11 Actual standard is titled ISO/IEC 9899:2011 last correction ISO/IEC 9899:2011/Cor 1:2012 from

5 Compilation and linking source code counter.c Compiler object code counter.o library code start-up code Linker executable code counter.out/.exe Figure: Compilation of C language source code.

6 Software development tools Windows general: Microsoft Visual Studio C++ Builder Dev-C++ using free tool GCC GNU Compiler Collection Windows AVR: AVR Studio + WinAVR CodeVisionAVR IAR Embedded Workbench Keil Linux: gcc-avr, binutils-avr, avr-libc, avrdude,... Eclipse (IDE), eclipse-cdt (C/C++ plugin)

7 Source Code Compilation 1 LDI R28, 0 x5f // (! ) 2 LDI R29, 0 x04 // (! ) 3 OUT 0x3E, R29 // (! ) 4... OUT 0x3D, R28 // (! ) 5 DDRB = 0 xff SER R24 SER R24 6 OUT 0x17, R24 OUT 0x17, R24 7 temp = 0 x03 LDI R24, 0 x03 LDI R24, 0 x03 8 STS 0 x0060, R24 // (! ) 9 PORTB = temp OUT 0x18, R24 OUT 0x18, R24 10 w h i l e ( 1 ) IN R24, 0 x18 // (! ) 11 PORTB SUBI R24, 0 x01 DEC R24 12 RJMP PC 0x0003 RJMP PC 0x0002 Figure: Compilation of C language source code. Rem.: STS k, Rr - Store Direct to Data Space (0 r 31, 0 k ).

8 FYI: Intel HEX Format Description Table: Machine language in Intel HEX format.... : D4E0 DEBF CDBF 8FEF 87BB 83E ED :08 00A BB 88B FCCF 3E Meaning of control bytes in Intel HEX format: : Beginning of line. 10 Number of data bytes in one line (in hexadecimal) Address of first data byte (0x0048 2=0x0090). 00 Code type (for AVR, 00 coresponds with 64 kb memory page).... Data in machine language (LSB first). ED Control checksum of one line without :. All bytes are added. From results, the two s complement of LSB is calculated. Checksum: A BB B FC + CF = $5C2 C2 3E.

9 Basic Principles in C Language Programming All commands end by semicolon. Bodies of functions, conditions, cycles, etc. are grouped inside the braces {. Strings are enclosed by quotation marks " ". Comments are introduce by double slash //, or are enclosed by /*... */. Using of reserved words is strictly observed: for, return, switch, case, if, else, char, int, float, unsigned, void,... Function prototype declares type of return address, number and types od input parameters. E.g. int imax( int, int ) Function declaration: return value function name( par0, par1,... ) { // body of function

10 Structure of C Code Typical C program #include preprocessor instructions int main( void ) function a( ) main() is always the first function called statements functions are made up of statements statements function b( ) functions are the building blocks of C statements declaration assignment function control... Figure: Anatomy of a C code.

11 Function Prototype 1 /* Header f i l e s */ 2 #i n c l u d e <a v r \ i o. h> // h e a d e r f i l e f o r MCU 3 4 /* F u n c t i o n p r o t o t y p e s */ 5 v o i d setup ( v o i d ) // s e t u p f u n c t i o n p r o t o t y p e 6 i n t key_pressed ( void ) // k e y p r es s e d funct. prototype 7 8 /* G l o b a l v a r i a b l e s */ 9 char temp // d e c l a r a t i o n o f 8 b i t v a r. temp i n t main ( v o i d ) { 12 setup ( ) // c a l l s e t u p f u n c t i o n 13 f o r ( ) { // f o r e v e r l o o p 14 i f ( key_pressed ( ) ) { // body o f c o n d i t i o n r e t u r n ( 1 ) // r e t u r n v a l u e = v o i d setup ( v o i d ) { // set input / output ports // body o f f u n c t i o n i n t key_pressed ( void ) { // r e t u r n code o f p r e s s e d key // body o f f u n c t i o n 26

12 Tips on Making Programs Readable Choose meaningful variable names and use comments. Note that these two techniques complement each other. Using blank lines to separate one conceptual section of a function from another. (C does not require the blank line, but it enhances readability.) Use one line per statement. C has a free-form format. (1) (2) 1 i n t main ( v o i d ) { i n t four four 2 = printf ( 6 %d\n, 7 four ) r e t u r n 0 i n t main ( v o i d ) { i n t four = 4 printf ( %d\n, four ) r e t u r n 0

13 Variables All variables are identified by its name and type and must be declared before using: char temp // 8-bit signed number unsigned int ii // 16-bit unsigned number float f = 3.14 // 32-bit floating point number // with assignment According to accessibility, each variable could be: Local: Allocated in stack or heap memory part while the function is executed. Global: Allocated during compiling process, accessible for all functions. Type Size [b] Range char unsigned char signed char int unsigned int float 32 ±1, ±3,

14 Arithmetic and Binary Operations Table: Arithmetic operations Operation Operand Multiplication * Division / Modulo division % Addition + Subtraction - Incrementation ++ Decrementation -- Table: Binary operations Operation Operand One s complement ~ Left shift << Right shift >> Logical AND & Logical OR Logical EX-OR ^ Simplified entry: a += 3 // a=a+3 a++ // a=a+1 b -= 2 // b=b-2 c *= 5 // c=c*5 d /= a // d=d/a Simplified entry: a = 3 b &= 2 c ^= 5 d <<= 2

15 Condition Condition: if if( condition ) { else { Condition switch switch( variable ) { case value0: case value1: default: Table: Condition operators Operation Operand Equal to == Not equal to!= Less than < Less than or equal <= Greater than > Greater than or equal >=

16 Loops Loop: for for( par0 par1 par2 ) { Loop: while while( condition ) { Forever loop: for for( ) { Forever loop: while (a) while( 1 ) { (b) while( 1 )

17 Special Functions of GCC and AVR Libc Bit value testing in control register: if( bit is set( register, bit )) { if( bit is clear( register, bit )) { Loop with bit value testing: loop until bit is set( register, bit ) { loop until bit is clear( register, bit ) {

19 Combination of Assembly and C Language Programming in C language is simpler, faster, and code could be portable between diferent processor platforms. Compiled code allocated more space in program memory, thus its execution is slower. Common practice is to program entire application in C language, and only critical parts should be reprogrammed in assembly language. In these parts we obtain absolute control of instruction number and program velocity. Assembly language inserting into C language by asm() function: asm( "SEI" ) asm( "LDI R16, 0x20\nINC R16\n" ) Compiled: SEI LDI R16, 0x20 INC R16

20 FYI: Parameters Transfer Between Assembly and C Language výst hodnota Pracovní registry 7 0 { R8 R9 R22 R23 R24 R25 vst param 8 vst param 1 vst param 0 For parameters transfer between ASM and C code, the predetermined registers are used: Input parameter 0: R25:R24, Input parameter 1: R23:R22,... Input parameter 8: R9:R8, Function return value: R25:R24. Ex.: extern int add compl( int,int ) Calling of ASM function for complex addition from C code: c = add compl( a,b ) First complex operand: R25:R24 Second complex operand: R23:R22 Returned complex addition value: R25:R24

22 Interrupt Service Routine in C Language While interrupt routines are used, the header file interrupt.h have to be included in C source code. For programmers there is no need to: Stack definition in source code the compiler do it automatically. Know the concrete addresses of interrupt vectors. ISR (Interrupt Service Routine) is programmed by macro ISR( parameter ), while parameter stands for an interrupt source identification: INT0 vect External Interrupt Request 0, ADC vect ADC Conversion Complete.... All informations and code examples are valid only for GCC with AVR Libc.

23 ISR Parameters for ATmega16 Vector No. Program Address ISR Input Parameter 1 0x x0002 INT0 vect 3 0x0004 INT1 vect 4 0x0006 TIMER2 COMP vect 5 0x0008 TIMER2 OVF vect 6 0x000A TIMER1 CAPT vect 7 0x000C TIMER0 COMPA vect 8 0x000E TIMER0 COMPB vect 9 0x0010 TIMER1 OVF vect 10 0x0012 TIMER0 OVF vect 11 0x0014 SPI STC vect 12 0x0016 USART RXC vect 13 0x0018 USATRT UDRE vect 14 0x001A USART TXC vect 15 0x001C ADC vect 16 0x001E EE RDY vect 17 0x0020 ANA COMP vect 18 0x0022 TWI vect 19 0x0024 INT2 vect 20 0x0026 TIMER0 COMP vect 21 0x0028 SPM RDY vect

24 Interrupt Service Routine in C Language 1 #i n c l u d e <a v r / i o. h> // i n c l u d e d e f i n i t i o n f i l e f o r Atmel MCU 2 #i n c l u d e <a v r / i n t e r r u p t. h> // i n c l u d e i n t e r r u p t r o u t i n e s 3 4 /* g l o b a l v a r i a b l e s */ 5 char counter = 0 // b i n a r y c o u n t e r 6 7 /* main a p p l i c a t i o n */ 8 i n t main ( v o i d ) 9 { 10 /* p o r t s e t t i n g s */ 11 DDRD = 0xf0 // set port D: 4 b i t output 4 b i t input 12 PORTD = // t u r n o f f a l l LEDs /* i n t e r r u p t s e t t i n g s */ 15 /* t i m e r / c o u n t e r 1 */ 16 TCCR1B = (1<<CS12 ) (0<<CS11 ) (0<<CS10 ) 17 // s e t p r e s c a l e r 256 f o r 16 b i t t i m e r / c o u n t e r 1 18 TIMSK = (1<<TOIE1 ) // e n a b l e i n t e r r u p t f o r t i m e r / c o u n t e r 1 o v e r f l o w sei ( ) // e n a b l e a l l i n t e r r u p t s w h i l e ( 1 ) /* f o r e v e r l o o p */ 23 r e t u r n (1) /* r e t u r n from main f u n c t i o n */ /* i n t e r r u p t s */ 27 /* i n t e r r u p t r o u t i n e f o r t i m e r / c o u n t e r 1 o v e r f l o w */ 28 ISR ( TIMER1_OVF_vect ) 29 { 30 counter = 16 // change 4 b i t binary counter value 31 PORTD = counter // d i s p l a y b i n a r y c o u n t e r v a l u e 32