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Lecture 5: Interrupts in Turbo C++

Lecture 5: Interrupts in Turbo C++. Concepts of Interrupts Programs for interrupts: Keyboard Video Time. Execution of an Instruction (review). Fetch the instruction from the memory. Execution of an instruction is achieved by a sequence of commands issues by the control unit.

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Lecture 5: Interrupts in Turbo C++

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  1. Lecture 5: Interrupts in Turbo C++ • Concepts of Interrupts • Programs for interrupts: • Keyboard • Video • Time CS3369 Real Time Control Software/DENG Xiaotie

  2. Execution of an Instruction (review) Fetch the instruction from the memory Execution of an instruction is achieved by a sequence of commands issues by the control unit. Fetch the operands from the memory Perform the operation Update the program counter no Check interrupt yes Interrupt processing Next Instruction CS3369 Real Time Control Software/DENG Xiaotie

  3. Execution of a Program (review) Fetch the instruction from the memory Fetch the operands from the memory LOAD b, R1 Perform the operation Update the program counter A program is a sequence of instructions. no Check interrupt yes Fetch the instruction from the memory Fetch the operands from the memory Perform the operation ADD R1, 1 Update the program counter a = b + 1; no Check interrupt yes Fetch the instruction from the memory Fetch the operands from the memory • STORE R1, a Perform the operation Update the program counter no Check interrupt yes …... CS3369 Real Time Control Software/DENG Xiaotie

  4. Interrupt • Interrupt is a mechanism for diverting the attention of a processor when a particular event occurs, such as I/O device requests. • Interrupts cause a break in the normal execution of a program. CS3369 Real Time Control Software/DENG Xiaotie

  5. A Break in the Normal Execution of a Program Fetch the instruction from the memory Interrupt The execution of the program can be temporarily stopped to allow a special piece of software -- an interrupt service routine -- to run. When the routine has finished, the program resumes. + efficient and responsive - difficult to program Fetch the operands from the memory Perform the operation Update the program counter no Check interrupt yes Fetch the instruction from the memory Fetch the operands from the memory Perform the operation Interrupt Processing and Service Update the program counter Check interrupt yes Fetch the instruction from the memory Fetch the operands from the memory Perform the operation Update the program counter no Check interrupt yes Interrupt processing CS3369 Real Time Control Software/DENG Xiaotie

  6. Steps taken to process Interrupt 1. On receipt of the interrupt, the processor after executing the current instruction, branches to an interrupt processing routine. The routine is commonly known as Interrupt Handler. 2. The Interrupt Handler will save the current processor data (registers, status register, PC) and determine which device has interrupt the processor (polling). 3. Execution then branches to the so called Interrupt Service Routine associated with the device (causing the interrupt) and the processor executes data transfer. 4. The interrupt system is enable so that further interrupts may be recognized. 5. Return to that program the execution of which was suspended after recognizing the interrupt. CS3369 Real Time Control Software/DENG Xiaotie

  7. Interrupt Processing and Service Disable interrupts Save environment Find out which device causes interrupt Branch to specific interrupt service routine ISR 1 ISR i ISR n Restore environment Enable interrupts CS3369 Real Time Control Software/DENG Xiaotie

  8. Interrupt Vectors • the segmented addresses that specify the locations of interrupt handlers are called interrupt “vectors” • an interrupt handler is a function/subroutine that takes care of the interrupt. • There are 256 interrupt vectors stored in interrupt vector table located at the beginning of the memory • some are reserved and some can be used by users CS3369 Real Time Control Software/DENG Xiaotie

  9. Types ofInterrupt • • Hardware Interrupts • • CPU Interrupts • • Software Interrupts CS3369 Real Time Control Software/DENG Xiaotie

  10. Hardware Interrupts Hardware interrupts are generated by device control and supervised by PIC (programmable interrupt control) chip. Interrupt No. Functions • 0x02 NMI: non-maskable interrupt, memory parity • 0x08 timer (18 per second) • 0x09 keyboard • 0x0A interrupt from controller 2 • 0x0B, 0x0C serial port2,1 • 0x0D parallel port 2 • 0x0E diskette • 0x0F parallel port 1 (for printer) Here, NMI has top priority and is serviced immediately, and it cannot be turned off. It occurs due to some significant error, such as power failure. HERE: 0x stands for hexadecimal notations: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F, where A stands for ten, B eleven, C, twelve, D thirteen, E fourteen, F fifteen. Therefore, 0x200 is 2x16x16 plus 0 which is 512 in decimal. For decimal notations: 200=2x10x10. CS3369 Real Time Control Software/DENG Xiaotie

  11. CPU Interrupts CPU interrupts are generated in response to a fatal program error, or for program flow control • 0x00 division by zero • 0x01 generated after every instruction when in single-step mode • 0x02 generated when a program reaches a breakpoint set by user • 0x04 arithmetic overflow CS3369 Real Time Control Software/DENG Xiaotie

  12. Software Interrupts Software interrupts are generated by using the software interrupt instruction. In turbo C: #include <dos.h> geninterrupt(n); • BIOS interrupts: provides the most direct, low level interaction with the I/O devices and give a device-independent interface which hides all the details of the hardware architecture from programmers and includes interrupt numbers: 0x05, 0x10-0x1C, 0x48. • DOS interrupts: are parts and the DOS operating system, handle file and memory management and executive services: 0x20-0x60 • General use interrupts: can be written by users for their own service routines: 0x61-0x67 Notice: no need to remember all the interrupt vectors. Focus on CS3369 Real Time Control Software/DENG Xiaotie

  13. A Register INPUT OUTPUT Q D CLOCK D: data input Q: output of data in the register CS3369 Real Time Control Software/DENG Xiaotie

  14. Architecture of PC Registers Scratch-pad Registers AH BH CH DH AL BL CL DL • AX (accumulator) • BX (base) • CX (count) • DX (data) • CS (code segment) • DS (data segment) • SS (stack segment) • ES (extra segment) • IP (instruction pointer) • SP (stack pointer) • BP (base pointer) • SI (source index) • DI (destination index) • Flags 0 7 0 7 15 Segment Registers 0 Offset Registers 15 0 OF DF IF TF SF ZF AF PF CF CS3369 Real Time Control Software/DENG Xiaotie

  15. Access Registers in Turbo C REGISTERS PSUDO-VARIABLES in C • AX _AX (_AH _AL) • BX _BX (_BH, _BL) • CX _CX (_CH, _CL) • DX _DX (_DH, _DL) • CS _CS • DS _DS • SS _SS • ES _ES • SP _SP • BP _BP • SI _SI • DI _DI • Flags _FLAGS CS3369 Real Time Control Software/DENG Xiaotie

  16. The Flag Register in IBM PC 15 0 OF DF IF TF SF ZF AF PF CF IF is the interrupt flag which controls whether interrupts are enabled. IF=1: The CPU will deal with interrupt requests. IF=0: The CPU will ignore interrupt requests. CF Carry flag Indicates an arithmetic carry OF Overflow flag Indicates a signed arithmetic overflow ZF Zero flag Indicates a zero result or an equal comparison SF Sign flag Indicates a negative result or comparison PF Parity flag Indicates an even number of 1 bits AF Auxiliary carry flag …. DF Direction flag Controls increment direction in string operastions TF Trap flag Controls single-step operation (used by DEBUG). CS3369 Real Time Control Software/DENG Xiaotie

  17. BIOS Keyboard Services They are invoked with interrupt 0x16 with the following Service numbers in the register AH (_AH in Turbo C). • 0x00 Read Next Keyboard Character • 0x01 Report Whether Character Ready • 0x02 Get Shift Status • 0x03 Set Typematic Rate and Delay • 0x05 Keyboard Write • 0x10 Extended Keyboard Read • 0x11 Get Extended Keystroke Status • 0x12 Get Extended Shift Status service# functionality Notice: 1. Service numbers are parameters pass to the subroutines/interrupt handlers 2. Try to remember the meaning of service 0x00 and 0x01 for interrupt 0x16. CS3369 Real Time Control Software/DENG Xiaotie

  18. Each character is reported as a pair of bytes. The main byte returned in AL is either 0 for special characters, or an ASCII code for ASCII characters. The auxiliary byte returned in AH is either the character ID for special characters or the standard PC-keyboard scan code identifying the pressed key. Interrupt 0x16 Service 0x00 Service 0x00 reports the next keyboard input character. If there is no character in the BIOS keyboard buffer, it waits until one is ready. The character is removed from the BIOS keyboard buffer after it is read. To invoke this service to read a character into a variable x in Turbo C, we do: char x; _AH=0x0; geninterrupt(0x16); x=_AL; CS3369 Real Time Control Software/DENG Xiaotie

  19. char x; int y; _AH=0x0; geninterrupt(0x16); x=_AL; cout <<“The key is: ”<< x <<endl; declare x to be “char” type choose service 0x0 with _AH invoke interrupt 0x16 get ASCII code of key from _AL print the key out An Example of Getting a Key from Keyboard Remember to include dos.h in your file. CS3369 Real Time Control Software/DENG Xiaotie

  20. char get_key_number () { //return type of the function is char char a; _AH=0x00; //service number 0x00 geninterrupt(0x16); //interrupt 0x16 a=_AL; //_AL is the key return tmp; //return the value } A Function to get a key Demo the program A:key.cpp in the lecture. 1. Show the program 2. Run the program CS3369 Real Time Control Software/DENG Xiaotie

  21. Interrupt 0x16 Service 0x01 Service 0x01 tests whether a keyboard input character is ready. The zero flag (ZF) is used as the signal: 1 indicates no input is ready, 0 indicates a character is ready. In the latter case, the character is not removed from the BIOS keyboard buffer until it is read by service 0x00. To invoke this service in Turbo C, we do: char x; _AH=0x01; geninterrupt(0x16); To test whether a character is ready after the above steps in Turbo C, we do: if (_FLAGS&0x40==64); to check whether ZF is 1. CS3369 Real Time Control Software/DENG Xiaotie

  22. Use Keyboard BIOS to Read • To write a program to read a char from BIOS keyboard buffer, one may first use service 0x01 interrupt 0x16 to test whether there is a key stored in the BIOS buffer, then use service 0x00 interrupt 0x16 to read it. • int ch; • _AH=0x01; • geninterrupt(0x16); • temp=_FLAGS&0x40; • /*must put the data to temp, see slide 32 */ • if (temp==0) { • _AH=0; • geninterrupt(0x16); • ch=_AL; • } The difference is that the computer does not have to wait for users to type it. CS3369 Real Time Control Software/DENG Xiaotie

  23. Caution when using Pseudo-Variables Pseudo-variables refer to CPU registers which are used by other programs which may run at the same time. One must assign values right before using them and read values right after obtaining them, especially when we program in C. Be careful about the following: • A pseudo-variable has no address • The values one place in pseudo-variables may NOT be preserved for any length of time. • Values of pseudo-variables may not remain the same across a function call. • Do not change values of _CS, _SS, _SP, nor _BP since they are used by machine code produced by Turbo C compiler. CS3369 Real Time Control Software/DENG Xiaotie

  24. Write a function to get a character • int key_ready() {//return 1 if a key is ready, 0 otherwise • long int x; • _AH=1; //service number 0x01 • geninterrupt(0x16); //interrupt 0x16 • x=_FLAGS; //get flag register • if (x&0x40==0) {return 1;} //if ZF==0 a key is ready • else return 0; //else no key • } • char read_a_key() { //return char if a key is ready • if (key_ready()) • {return get_key_number().x;} • else return 0; • } CS3369 Real Time Control Software/DENG Xiaotie

  25. Shoot a bullet when press a key #include<dos.h> #include <graphics.h> #include<iostream.h> #include<conio.h> void show(int i,float h, float v); void erease(int i, float h, float v); void main(void) { int driver = DETECT,mode; int i,j,i1,s1; int y=1; initgraph(&driver,&mode,"D:\\bc31\\bgi"); setcolor(WHITE); line(1,400,400,400); for ( i = 0; i < 80; i++ ) { show(i, 5.0, 9.0); y=1; _AH=0x01; geninterrupt(0x16);// y=_FLAGS&0x40; if(y == 0) {s1=1;i1=i; _AH=0x00; geninterrupt(0x16);} if (s1==1) {show(i-i1, 10.0, 8.0); } delay (300); erease(i, 5.0, 9.0); if (s1==1) erease(i-i1, 10.0, 8.0); } closegraph(); } void show(int i, float h, float v) { int x, y; x=h*i; y=v*i-0.15*i*i; setcolor(RED); circle(400-x,400-y,2); } void erease(int i, float h, float v) { int x, y; x=h*i; y=v*i-0.15*i*i; setcolor(BLACK); circle(400-x,400-y,2); } CS3369 Real Time Control Software/DENG Xiaotie

  26. Video Interrupt Services(for general knowledge, will not be tested) Most of the useful video services are found in the BIOS through interrupt 0x10. Some MS-DOS video services are provided through interrupt 0x21. They are user programmed interrupts to produce output to the video screen. Usually, one puts the function/service number in the register AH and then invokes the corresponding interrupt. Very often there are some parameters for these functions/services which are put in register AL, BX, CX, or DX. CS3369 Real Time Control Software/DENG Xiaotie

  27. BIOS Video Service Interrupt 0x10 service#functionality service#functionality • 0x00 set video mode • 0x01 set cursor size • 0x02 set cursor position • 0x03 read cursor position • 0x04 read light-pen position • 0x05 set active display page • 0x06 scroll window up • 0x07 scroll window down • 0x08 read character/attribute • 0x09 write character/attribute • 0x0A write character • 0x0B set 4-color palette • 0x0C write pixel • 0x0D read pixel • 0x0E write char in tty mode • 0x0F get current video mode • 0x10 color palette interface • 0x11 char generator interface • 0x12 alternate select • 0x13 write character string • 0x14/15 (PC convertible only) • 0x1A read/wri. dsp. cmb. code • 0x1B return functionality • 0x1C save/restore video state CS3369 Real Time Control Software/DENG Xiaotie

  28. Interrupt 0x10 Service 0x0E: Write char in TTY mode . • The service number 0x0E is put in register AH. • The char to be written is put in AL. The display page number is put in BH and the foreground color is in BL. • The character is written at the cursor location, and the cursor is advanced one position, wrapping over to new line or scrolling the screen as needed. • There are four characters that service 0x0E reacts to according to their ASCII meaning: 0x07 beep, 0x08 backspace, 0x0A linefeed, 0x0D carriage return. All other characters are displayed normally. CS3369 Real Time Control Software/DENG Xiaotie

  29. Output Characters Display character “a” Feed a new line • _AH=0x0E; • _AL=0x0A; • _BH=1; • geninterrupt(0x10); • _AH=0x0E; • _AL=97; • _BH=1; • geninterrupt(0x10); Back one space Beep • _AH=0x0E; • _AL=0x08; • _BH=1; • geninterrupt(0x10); • _AH=0x0E; • _AL=0x07; • _BH=1; • geninterrupt(0x10); CS3369 Real Time Control Software/DENG Xiaotie

  30. A Function for Output a Char • void output_a_char(int x) { //x is the ASCII code of char • _AH=0x0E; • _AL=x; • _BH=1; • geninterrupt(0x10); • } Call the function to output characters • output_a_char(97); //output ‘A’ • output_a_char(8); //backspace • output_a_char(7); //output a ring • output_a_char(0x0A); //a new line CS3369 Real Time Control Software/DENG Xiaotie

  31. Another Function for Output a Char • void output2_a_char(char x) { //x is a char type • int tmp; • tmp=x; //convert to ASCII code • _AH=0x0E; //service number 0x0E • _AL=tmp; //output tmp • _BH=1; • geninterrupt(0x10); //interrupt 0x10 • } Call the function to output characters • output2_a_char(‘A’); //output “A” • output2_a_char(‘B’); //output “B” CS3369 Real Time Control Software/DENG Xiaotie

  32. Time Services (Clock) • Interrupt 0x21 Service 0x2C: • CH contains the hours (0-23) • CL contains the minutes (0-59) • DH contains the seconds (0-59) • DL contains hundredths of a second (0-99). CS3369 Real Time Control Software/DENG Xiaotie

  33. Time Services (Clock) • int i,j,k,l; • _AH=0x2C; //service 0x2C for get time • interrupt(0x21); //interrupt 0x21 • i=_CH; j=_CL; k=_DH; l=_DL; • cout<<i<<“ Hours”<<j<<“ Minutes ”<<k<<“ Seconds ”<<l; CS3369 Real Time Control Software/DENG Xiaotie

  34. Get the Time of Hitting a Key Using the above functions written with interrupts, we may obtain the approximate time of hitting a key as follows: int i,j,k,l; read_a_key(); /*call function read_a_key(); */ _AH=0x2C; //service 0x2C for get time interrupt(0x21); //interrupt 0x21 i=_CH; j=_CL; k=_DH; l=_DL; cout<<i<<“ Hours”<<j<<“ Minutes ”<<k<<“ Seconds ”<<l; CS3369 Real Time Control Software/DENG Xiaotie

  35. Arrays • An array is a collection of two or more adjacent memory cells, called array elements, that are associated with a particular symbolic name. To declare an array int x[3]; (We declared an array with name x. It contains 3 elements. Each is of int type.The index starts with 0) x[0] x[1] x[2] CS3369 Real Time Control Software/DENG Xiaotie

  36. Use an array in the program include <iostream.h> void main(void) { int x[10],i; for (i=0; i<=9; i++) cin>>x[i]; for (i=0; i<=9; i++) cout<< x[i]; } The index of the elements can change. The index of the first element of an array is 0. x[0], x[1], x[2], x[3], x[4] x[5], x[6], x[7], x[8], x[9] CS3369 Real Time Control Software/DENG Xiaotie

  37. Initialize an array include <iostream.h> void main(void) { int x[10]={1,2,2,2,3,4,5,6,7,9} ,i; for (i=0; i<=9; i++) cout<< x[i]<<“ ”; } CS3369 Real Time Control Software/DENG Xiaotie

  38. An array of characters include <iostream.h> void main(void) { char x[3]={‘a’, ‘b’, ‘c’} ,i; for (i=0; i<=9; i++) cout<< x[i]; } CS3369 Real Time Control Software/DENG Xiaotie

  39. Exercise What does the following program output? include <iostream.h> void main(void) { int x[10]={8, 7, 9, 10, 1, 3, 3, 8, 2, 5} , i, j; for (i=0; i<=9; i++) { for(j=9; j>i; j--) if (x[i]>x[j]) { y=x[i]; x[i]=x[j]; x[j]=y; } for(j=0; j<=9; j++) cout<< x[j]; cout<<“\n”; } } CS3369 Real Time Control Software/DENG Xiaotie

  40. Shoot bullets whenever press key +plane #include<dos.h> #include <graphics.h> #include<conio.h> void show(int i,float h, float v); void erease(int i, float h, float v); void planeshow(int i); void ereasep(int i); void main(void) { int driver = DETECT,mode; int i,j,i1,s1,k; int y=1; int a[100]; for(i=0; i<=99; i++) a[i]=0; initgraph(&driver,&mode,"D:\\bc31\\bgi"); setcolor(WHITE); line(1,400,400,400); j=1; for ( i = 0; i < 80; i++ ) { setcolor(BLUE); planeshow(5*i); setcolor(YELLOW); planeshow(5*(i-8)); show(i, 5.0, 9.0); y=1; _AH=0x01; geninterrupt(0x16);// y=_FLAGS&0x40; if(y == 0) {j=j+1;a[j]=i; _AH=0x00; geninterrupt(0x16);} for (k=2; k<=j; k++) if (a[k]!=0) {show(i-a[k], 10.0+0.5*k, 8.0+0.1*k); } delay (300); ereasep(5*i); ereasep(5*(i-8)); erease(i, 5.0, 9.0); for (k=2; k<=j; k++) if (a[k]!=0) {erease(i-a[k], 10.0+0.5*k, 8.0+0.1*k); } } closegraph(); } void show(int i, float h, float v) { int x, y; x=h*i; y=v*i-0.15*i*i; setcolor(RED); circle(400-x,400-y,2); } void erease(int i, float h, float v) { int x, y; x=h*i; y=v*i-0.15*i*i; setcolor(BLACK); circle(400-x,400-y,2); } void planeshow(int i) { int j; circle(i+5, 202, 2); circle(i+3, 204, 2); for (j=0; j<=8; j++) circle(i+j, 200, 2); circle(i+5, 198, 2); circle(i+3, 196, 2); } void ereasep(int i) { int j; setcolor(BLACK); circle(i+5, 202, 2); circle(i+3, 204, 2); for (j=0; j<=8; j++) circle(i+j, 200, 2); circle(i+5, 198, 2); circle(i+3, 196, 2); } CS3369 Real Time Control Software/DENG Xiaotie

  41. a-shoot bullet u-plane up i-plane down #include<dos.h> #include <graphics.h> #include<conio.h> void show(int i,float h, float v); void erease(int i, float h, float v); void planeshow(int i,int k); void ereasep(int i, int k); void main(void) { int driver = DETECT,mode; int i,j,i1,s1,k; int y=1,xx=0; char x; int a[100]; for(i=0; i<=99; i++) a[i]=0; initgraph(&driver,&mode,"a:\\bgi"); setcolor(WHITE); line(1,400,400,400); j=1; for ( i = 0; i < 80; i++ ) { setcolor(BLUE); planeshow(5*i, 5); show(i, 5.0, 9.0); y=1; _AH=0x01; geninterrupt(0x16); y=_FLAGS&0x40; if(y == 0) { _AH=0x00; geninterrupt(0x16); x=_AL; if (x == 'a') {j=j+1;a[j]=i;} if (x =='u' ) {sound(700); xx=xx-5;} if (x =='i' ) {sound(200); xx=xx+5;} } setcolor(YELLOW); planeshow(5*(i-8), xx); for (k=2; k<=j; k++) if (a[k]!=0) {show(i-a[k], 10.0+0.5*k, 8.0+0.1*k); } delay (300); nosound(); ereasep(5*i, 5); ereasep(5*(i-8), xx); erease(i, 5.0, 9.0); for (k=2; k<=j; k++) if (a[k]!=0) {erease(i-a[k], 10.0+0.5*k, 8.0+0.1*k); } } closegraph(); } void show(int i, float h, float v) { int x, y; x=h*i; y=v*i-0.15*i*i; setcolor(RED); circle(400-x,400-y,2); } void erease(int i, float h, float v) { int x, y; x=h*i; y=v*i-0.15*i*i; setcolor(BLACK); circle(400-x,400-y,2); } void planeshow(int i,int k) { int j; circle(i+5, 202+k, 2); circle(i+3, 204+k, 2); for (j=0; j<=8; j++) circle(i+j, 200+k, 2); circle(i+5, 198+k, 2); circle(i+3, 196+k, 2); } void ereasep(int i, int k) { int j; setcolor(BLACK); circle(i+5, 202+k, 2); circle(i+3, 204+k, 2); for (j=0; j<=8; j++) circle(i+j, 200+k, 2); circle(i+5, 198+k, 2); circle(i+3, 196+k, 2); } CS3369 Real Time Control Software/DENG Xiaotie

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