Embedeeeeeeeeeeeeeeeeeeeeeeeeeeeded C.pptx

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1. EMBEDDED C DR. A.GUNASUNDARI ASST. PROFESSOR EEE, PSGTECH

2. Embedded Software Programming Languages Common programming languages are assembly languages and C use of microprocessor-specific assembly-only as the programming language As time progressed embedded systems moved onto C as the embedded programming language of choice. C is the most widely used programming language for embedded processors/controllers AGS,EEE,PSGCT 2

3. Structure of Assembly Language In the early days of the computer, programmers coded in machine language, consisting of 0s and 1s Tedious, slow and prone to error Assembly languages, which provided mnemonics for the machine code instructions, plus other features, were developed An Assembly language program consist of a series of lines of Assembly language instructions Assembly language is referred to as a low level language It deals directly with the internal structure of the CPU AGS,EEE,PSGCT 3

4. Structure of Assembly Language Assembly language instruction includes a mnemonic (abbreviation easy to remember) - the commands to the CPU, telling it what those to do with those items optionally followed by one or two operands - the data items being manipulated A given Assembly language program is a series of statements, or lines Assembly language instructions - Tell the CPU what to do Directives (or pseudo-instructions) - Give directions to the assembler AGS,EEE,PSGCT 4

5. Structure of Assembly Language AGS,EEE,PSGCT 5

6. The step of Assembly language program are outlines as follows: 1) First we use an editor to type a program,many excellent editors or word processors are available that can be used to create and/or edit the program Notice that the editor must be able to produce an ASCII file For many assemblers, the file names follow the usual DOS conventions, but the source file has the extension “ asm “ or “ src ”, depending on which assembly you are using AGS,EEE,PSGCT 6

7. 2) The “ asm ” source file containing the program code created in step 1 is fed to an 8051 assembler The assembler converts the instructions into machine code The assembler will produce an object file and a list file The extension for the object file is “ obj ” while the extension for the list file is “ lst ” 3) Assembler require a third step called linking The linker program takes one or more object code files and produce an absolute object file with the extension “abs” This abs file is used by 8051 trainers that have a monitor program AGS,EEE,PSGCT 7

8. 4) Next the “abs” file is fed into a program called “OH” (object to hex converter) which creates a file with extension “hex” that is ready to burn into ROM This program comes with all 8051 assemblers Recent Windows-based assemblers combine step 2 through 4 into one step AGS,EEE,PSGCT 8

9. lst File The lst (list) file, which is optional, is very useful to the programmer It lists all the opcodes and addresses as well as errors that the assembler detected The programmer uses the lst file to find the syntax errors or debug AGS,EEE,PSGCT 9

10. Examine the list file and how the code is placed in ROM AGS,EEE,PSGCT 10

11. After the program is burned into ROM, the opcode and operand are placed in ROM memory location starting at 0000 1. When 8051 is powered up, the PC has 0000 and starts to fetch the first opcode from location 0000 of program ROM Upon executing the opcode 7D, the CPU fetches the value 25 and places it in R5 Now one instruction is finished, and then the PC is incremented to point to 0002, containing opcode 7F 2. Upon executing the opcode 7F, the value 34H is moved into R7 The PC is incremented to 0004 AGS,EEE,PSGCT 11

12. 3. The instruction at location 0004 is executed and now PC = 0006 4. After the execution of the 1-byte instruction at location 0006, PC = 0007 5. Upon execution of this 1-byte instruction at 0007, PC is incremented to 0008 This process goes on until all the instructions are fetched and executed The fact that program counter points at the next instruction to be executed explains some microprocessors call it the instruction pointer AGS,EEE,PSGCT 12

13. Advantages of C It is simpler to learn, understand, program and debug. C Compilers are available for almost all embedded devices, and there is a large pool of experienced C programmers. Processor-independence and is not specific to any particular microprocessor/ microcontroller or any system. This makes it convenient for a user to develop programs that can run on most of the systems. As C combines functionality of assembly language and features of high level languages, C is treated as a ‘middle-level computer language’ or ‘high level assembly language’. C language is fairly efficient and supports access to I/O and provides ease of management of large embedded projects. Compilers are available for every embedded processor (8-bit to 32-bit). AGS,EEE,PSGCT 13

14. ‘C’ Versus Embedded ‘C’ C Language Embedded ‘C’ ‘C’ is a well structured, well defined and standardized general purpose programming language. Embedded ‘C’ can be considered as a subset of ‘C’ language. ‘C’ is used for desktop computers Embedded ‘C’ is for microcontroller based applications ‘C’ has the luxury to use resources of a desktop PC like memory, OS, etc. on desktop systems Embedded ‘C’ has to use with the limited resources (RAM, ROM, I/Os) on an embedded processor Compilers for ‘C’ (ANSI C) typically generate OS dependant executables Embedded ‘C’ requires compilers (Cross Compilers) to create files to be downloaded to the microcontrollers / microprocessors where it needs to run AGS,EEE,PSGCT 14

15. Compilers Vs Cross Compiler Compilers Cross Compiler It is a software tool that converts a source code written in a high level language to machine code. is a compiler capable of creating executable code for a platform other than the one on which the compiler is run. Generally compilers are used for desktop applications. Cross compiler tools are generally found in use to generate compiles for embedded system AGS,EEE,PSGCT 15

16. Storage Classes A storage class decides scope, visibility and lifetime of a variable. ‘C’ supports the following storage classes. – Auto (automatic variables) – Extern (external variables) – Static (static variables) – Register (register variables) AGS,EEE,PSGCT 16

17. Auto: A variable declared inside a function without any storage class specification, is by default an Auto (automatic) variable. They are created when a function is called and are destroyed automatically when the function exits. Automatic variables can also be called local variables because they are local to a function. By default they are assigned garbage value by the compiler. Extern (External or Global variable): A variable that is declared outside of any function is a Global variable. Global variables remain available throughout the program. One important thing to remember about global variable is that their values can be changed by any function in the program. The extern keyword is used before a variable to inform the compiler that this variable is declared somewhere else. The extern declaration does not allocate storage for variables. Storage Classes contd …. AGS,EEE,PSGCT 17

18. Storage Classes contd …. Static: A static variable tells the compiler to persist the variable until the end of program. Instead of creating and destroying a variable every time when it comes into and goes out of scope. Static is initialized only once and remains into existence till the end of program. Static variables are assigned ‘0’(zero) as default value by the compiler. Register: variable inform the compiler to store the variable in register instead of memory. Register variable has faster access than normal variable. Frequently used variables are kept in register. Only few variables can be placed inside register. Note that we can never get the address of such variables. AGS,EEE,PSGCT 18

19. Data Types various type of data types in C : unsigned char The character data type is the most natural choice. 8051 is an 8-bit microcontroller and unsigned char is also an 8-bit data type in the range of(0 –255)(00 –FFH). C compilers use the signed char as the default data types if we do not put the keyword unsigned char. We always use unsigned char in program until and unless we don’t need to represent signed numbers for example Temperature. AGS,EEE,PSGCT 19

20. Signed char The signed char is an 8-bit data type. signed char use the MSB D7 to represent –or +. signed char give us values from –128 to +127. unsigned int The unsigned int is a 16-bit data type. Takes a value in the range of 0 to 65535 (0000 –FFFFH) Define 16-bit variables such as memory addresses Set counter values of more than 256 Since registers and memory accesses are in 8-bit chunks, the misuse of int variables will result in a larger hex file. signed int Signed int is a 16-bit data type. use the MSB D15 to represent –or +. We have 15 bits for the magnitude of the number from –32768 to +32767. AGS,EEE,PSGCT 20

21. sbit (single bit) The bit data type allows access to single bits of bit-addressable memory spaces 20 –2FH sfr To access the byte-size SFR registers, we use the sfr data type. AGS,EEE,PSGCT 21

22. Variables in Embedded C AGS,EEE,PSGCT 22

23. Template for Embedded C Program #include <reg51.h> void main() { // body of the program goes here } - the first line of the template is the C directive “#include <reg51.h>” - this tells the compiler that during compilation, it should look into this file for symbols not defined within the program - “reg51.h” file simple defines the internal special function registers and their addresses AGS,EEE,PSGCT 23

24. 1. An embedded C program to load a number into Accumulator. # include <reg52.h> void main( ) { Acc = 0x25; } 2. Write a program to load three numbers into Accumulator and send them to port 1 # include <reg52.h> void main( ) { Acc = 0x25; P1 = Acc; Acc = 0x46; P1 = Acc; Acc = 0x92; P1 = Acc; } AGS,EEE,PSGCT 24

25. Write an 8051 C program to toggle all the bits of P1 continuously. //Toggle P1 forever #include <reg52.h> void main( ) { for ( ; ; ) { P1=0 x 55; P1=0 x AA; } } Part of the program to be repeated indefinitely must then be placed in between the curly brackets after the for(;;) statement. AGS,EEE,PSGCT 25

26. Write a C program for 8051 to transfer the letter “A” serially at 9600 baud continuously. Use 8-bit data and 1 stop bit. #include <reg51.h> void main( ) { TMOD = 0x20; //use Timer 1, mode 2 TH1= 0xFD; //9600 baud rate SCON = 0x50; //configure SCON TR1 = 1; // start the timer 1 while (1) { SBUF = ‘A’; //place value in buffer while (TI = = 0); TI = 0; } } AGS,EEE,PSGCT 26

27. */ Program for timer mode1 #include <reg52.h> /* Include x51 header file */ sbit test = P1^0; /* set test pin0 of port1 */   void timer delay() /* Timer0 delay function */ { TH0 = 0xFC; /* Load higher 8-bit in TH0 */ TL0 = 0x74; /* Load lower 8-bit in TL0 */ TR0 = 1; /* Start timer0 */ while(TF0 == 0); /* Wait until timer0 flag set */ TR0 = 0; /* Stop timer0 */ TF0 = 0; /* Clear timer0 flag */ } void main() { TMOD = 0x01; /* Timer0 mode1 (16-bit timer mode) */ while(1) { test = ~test; /* Toggle test pin */ timer_delay (); /* Call timer0 delay */ } } AGS,EEE,PSGCT 27

28. */ Program for timer mode1 #include <reg51.h> /* Include x51 header file */ sbit test = P1^0; /* set test pin0 of port1 */   void main() { TMOD = 0x20; /* Timer1 mode2 (8-bit auto reload timer mode) */ TH1 = 0xA4; /* Load 8-bit in TH1 */ TL1 = 0xA4; /* Load 8-bit in TL1 once */ TR1 = 1; /* Start timer1 */ while(1) { test = ~test; /* Toggle test pin */ while(TF1 == 0); /* Wait until timer1 flag set */ TF1 = 0; /* Clear timer1 flag */ } } AGS,EEE,PSGCT 28