Hacking JOSH – Operating System Development in Assembly

In this project I was able to develop a simple OS which have kernel and a Shell by configuring a given simple OS. You can find that preliminary OS  by reading this article,


http://asiri.rathnayake.org/articles/hacking-josh-operating-system-tutorial/

I implemented a new command for my operating system which prints hardware information about the computer.To achieve that functionality after some research work over the internet and experts of this area I found several waysto get hardware information using x86 Assembly language.
They were BIOS interrupt calls, CPUID instruction, BIOS data area, SMBIOS – Collection of tables which can provides you hardware information. In these methods I choose interrupt calls, CPUID instruction to display hardware information of the system.
In my function which I add to existing kernel  it can show Processor Brand, Processor Type, Ram Size, system date and time, check the availability of serial ports, floppy drives, printers, co-processors and mouse.
Following articles will explain the steps which I took to develop this operating system, It will explain step by step to develop a OS like that.

http://www.insightforfuture.blogspot.com/2010/11/useful-techniques-in-assembly.html
http://www.insightforfuture.blogspot.com/2010/11/x86-assembly-if-else-control-structures.html
http://www.insightforfuture.blogspot.com/2010/11/bios-interrupt-calls-to-get-hardware.html
http://www.insightforfuture.blogspot.com/2010/11/find-hardware-infodo-you-know-how.html
http://www.insightforfuture.blogspot.com/2010/11/smbios-gives-hardware-specifications.html

Next I will Explain the source code of this new functionality,

This is the shell command which is responsible for run the hardware info;

    hwi:                    ;;;;;;;;This is the place hardware info Procedure Starts
    mov SI,strCmd0               
    mov DI,hw               
    call os_string_strincmp            ;check is the entered command is HW_Info
    jc    hardware_info            ;if it is call the hardware info function
    jmp _cmd_ver                ;else go to next shell command
    else:
    jmp _cmd_done ;;;;;;;;;End of the Hardware info call

This is the code where the original functionality lies, These assembly code are responsible to retrieve hardware info by using interrupt calls.

;;;;;;;;;;;;;;Start of Hardware Info;;;;;;;;;;;;;;

hardware_info:

    mov si,ent   
    call    _disp_str   

    mov si,hwinfo
    call    _disp_str   

    mov si,ent   
    call    _disp_str   

;;;;;;;;;;;;Processor Info Display;;;;;;;;;;;;;;;;   

    mov si,pinfo
    call    _disp_str

    mov eax,0
    cpuid
    mov [vendor_id],ebx            ;getting the cpu brand from ebx,ecx,edx
    mov [vendor_id+4],edx
    mov [vendor_id+8],ecx
    mov si,processor
    call    _disp_str
    mov si,vendor_id
    call    _disp_str

    mov si,ent   
    call    _disp_str

    mov si,processort
    call    _disp_str

    mov eax,80000002h
    cpuid
    mov [processor_type],eax        ;getting the cpu type string  brand from ebx,ecx,edx,eax
    mov [processor_type+4],ebx
    mov [processor_type+8],ecx
    mov [processor_type+12],edx
    mov si,processor_type
    call    _disp_str

    mov eax,80000003h
    cpuid
    mov [processor_type1],eax
    mov [processor_type1+4],ebx
    mov [processor_type1+8],ecx
    mov [processor_type1+12],edx
    mov si,processor_type1
    call    _disp_str       
   
    mov eax,80000004h
    cpuid
    mov [processor_type2],eax
    mov [processor_type2+4],ebx
    mov [processor_type2+8],ecx
    mov [processor_type2+12],edx
    mov si,processor_type2
    call    _disp_str

    mov si,ent   
    call    _disp_str

    ;;;;;;;;;;;;;;;RAM Info Display;;;;;;;;;;;;;;;;;;

    mov si,rinfo
    call    _disp_str
    mov si,ram   
    call    _disp_str

    MOV AX, 0xE801
    INT 0x15                ;calling the intruupt to get ram size in 64kb blocks
    call hex2dec

    mov si,ent   
    call    _disp_str

    ;;;;;;;;;;;;;;;Other Info Display;;;;;;;;;;;;;;;;;
    int 11h                ;calling the intruupt to get pheriperal device info
    mov cx,ax

    mov si,oinfo
    call    _disp_str

    ;;;;;;;;;;;;;;Check for Floppy Drive;;;;;;;;;;;;;;

    and ax,1h
    cmp ax,0h
    jz ifblock0
    jmp elseblock0
    ifblock0:
    mov si, floppyNotPresent
    call    _disp_str
        jmp end0
    elseblock0:
    mov si, floppyPresent
    call    _disp_str
    end0:
    mov ax,cx   
   
    ;;;;;;;;;;;;;;Check for Math Co-Processor;;;;;;;;

    and ax,2h
    cmp ax,0h
    jz ifblock1
    jmp elseblock1
    ifblock1:
    mov si, mathaNotPresent
    call    _disp_str
        jmp end1
    elseblock1:
    mov si, mathaPresent
    call    _disp_str
    end1:
    mov ax,cx   

    ;;;;;;;;;;;;;Check for Joystick;;;;;;;;;;;;;;;;;;

    and ax,800h
    cmp ax,0h
    jz ifblock2
    jmp elseblock2
    ifblock2:
    mov si, joyNotPresent
    call    _disp_str
        jmp end2
    elseblock2:
    mov si, joyPresent
    call    _disp_str
    end2:
    mov ax,cx   

    ;;;;;;;;;;;;;Check for Serial Printer;;;;;;;;;;;;;

    and ax,1000h
    cmp ax,0h
    jz ifblock3
    jmp elseblock3
    ifblock3:
    mov si, printerNotPresent
    call    _disp_str
        jmp end3
    elseblock3:
    mov si, printerPresent
    call    _disp_str
    end3:
    mov ax,cx   

    ;;;;;;;;;;;;Check for Serial Ports;;;;;;;;;;;;;;;;

    and ax,700h

    cmp ax,0h
    jz ifblock4_s0
    ifblock4_s0:
    mov si, s0
    call    _disp_str
        jmp end4 
    
    cmp ax,100h
    jz ifblock4_s1
    ifblock4_s1:
    mov si, s1
    call    _disp_str
        jmp end4

    cmp ax,200h
    jz ifblock4_s2
    ifblock4_s2:
    mov si, s2
    call    _disp_str
        jmp end4
    cmp ax,300h
    jz ifblock4_s3
    ifblock4_s3:
    mov si, s3
    call    _disp_str
        jmp end4
    cmp ax,400h
    jz ifblock4_s4
    ifblock4_s4:
    mov si, s4
    call    _disp_str
        jmp end4
    cmp ax,500h
    jz ifblock4_s5
    ifblock4_s5:
    mov si, s5
    call    _disp_str
        jmp end4
    cmp ax,600h
    jz ifblock4_s6
    ifblock4_s6:
    mov si, s6
    call    _disp_str
        jmp end4

    cmp ax,700h
    jz ifblock4_s7
    ifblock4_s7:
    mov si, s7
    call    _disp_str
        jmp end4
    end4:
    mov ax,cx   

    ;;;;;;;;;;;;;;Check for Mouse;;;;;;;;;;;;;;;;

     int 33h                  ; call interrupt 33h function 0
     cmp ax,0ffffh            ; compare AX and FFFFh (installed)
     jz endmouse              ; it is? Jump to the end!
     mov si, nmouse
     call    _disp_str
     jmp end5
    endmouse:
     mov si, mouse
     call    _disp_str    
    end5:

    ;;;;;;;;;;;;;;Display Date and Time;;;;;;;;;;;;

    call os_get_date_string
    mov si,date_time
    call    _disp_str        
    mov si, BX
    call    _disp_str
    call os_get_time_string
    mov si, space
    call    _disp_str
    mov si, BX
    call    _disp_str

    ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
jmp else

If you want further info about this please contact me.

Inductive Loop Sensor & Dynamic Traffic Control for Intelligent Traffic Light System

Our Intelligent Traffic Light System is capable of changing priority level of the roads according to their traffic level. To measure the traffic level we have several mechanisms.

• Image Processing
• Pressure sensors, give reading when pressure changes by the vehicles
• Inductive Loops

From the above methods we choose inductive loop.It is build on the concept of inductance change of a coil when a metal object come closer.You know that when you send electrical current through a wire, it generates a magnetic field. For a coil this electromagnetic field is high.You can change the inductance of the coil and change the electromagnetic flux by introducing additional conductive materials into the loop's magnetic field. This is what happens when a car pulls up to the intersection. The huge mass of metal that makes up your car alters the magnetic field around the loop, changing its inductance. 

So we have made a coil develop the inductive loop.We have some kind of metering device to meter the voltage level change in the coil. After some reading we have found this article, it really help to achieve our target.

In the above  circuit diagram we can connect the LED's positive pin to PIC device to get the input. So using that we can easily develop a algorithm to achieve dynamic traffic controlling.

References : Above diagrams and pictures are extracted from the following resources on the purpose to gather all the knowledge in to one place for learn easily.

1. http://www.fhwa.dot.gov/publications/publicroads/98septoct/loop.cfm
2. http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/red-light-camera1.htm
3. http://www3.telus.net/chemelec/Projects/Loop-Detector/Loop-Detector.htm

8*6 LED Matrix for Intelligent Traffic Light System

Next Task was to make the controlling mechanism for traffic lights. Major problem was, there are not enough I/O pins in the PIC to control each bulb of the traffic light. So we choose small mechanism to avoid that problem. That is the 8*6 LED Matrix. To explain this concept I will use a article publish by electronic department of our university. (http://www.ent.mrt.ac.lk/web/knowledgebase/uc/5.3.pdf) . Here we use the mechanism used to light up pixels in a LCD display. I will explain the steps to light up all the 40 LEDs using this mechanism at same time.

 
• To light a single LED in this matrix we have to give +,- voltages to its pins. You can notice that if we set any pin in PORTB to logic 1, it will give + voltage to LED's + pin. 
• Then How we can give the ground connection to the - pin of the LED. For that we have to turn on the D400 transistor for that particular column.
• After that particular LED will be light up. For example we can use this code to light up all the LEDS RA0 column,
        PORTB=0b11111111;
        PORTA=0b00000001;
• To light up all the LEDS RA1 column,
        PORTB=0b11111111;
        PORTA=0b00000010;
• To light up all the LEDS RA2 column,
        PORTB=0b11111111;
        PORTA=0b00000100;
• To light up all the LEDS RA3 column,
        PORTB=0b11111111;
        PORTA=0b00001000;
• To light up all the LEDS RA4 column,
        PORTB=0b11111111;
        PORTA=0b00010000;
• To light each other LED in RA0 Column you can use this code,
        PORTB=0b10101010;
        PORTA=0b00000001;
• Like that we can control each LED in a column using PORTB pins.But you can identify that you cant light up RA0 columns 0the row LED and off the   RA1 columns 0the row LED at the same time. Because we use PORTA pins to choose the column and PORTB to choose the row.
• So how can we light up all the columns at same time. We use the weakness of human eye to this.If we light different columns at high speed you cant see a difference you will notice that all the LEDs are lighting at the same time.
• Here is the code for that,
  while(1){
        PORTB=0b10101010;
        PORTA=0b00000001;
        PORTB=0b10101010;
        PORTA=0b00000010;
        PORTB=0b10101010;
        PORTA=0b00000100;
        PORTB=0b10101010;
        PORTA=0b00001000;
        PORTB=0b10101010;
        PORTA=0b00010000;
  }
• In the same mechanism we implement the control system for our traffic light system. Below diagram will show you how we implement that.

Bluetooth Wireless Communication method for Intelligent Traffic Light System

• We choose Arduino Bluetooth Module Slave Wireless Serial Port 4P for our wireless communication purposes (http://www.ebay.com/itm/Arduino-Bluetooth-Module-Slave-Wireless-Serial-Port-4P-/150653185968?pt=LH_DefaultDomain_0&hash=item2313a12fb0).

  
  
  
  
  
  To use this device in the mood working 100% correct, we have to use a resistor divider to reduce the operating  Because PIC18f452's RX,TX operating in 5V-0V range but in this Bluetooth reviver it operates in 3.3V to 0V range. So we put up a voltage divider between the Arduino Bluetooth Module Slave Wireless Serial Port and the PIC's RX, TX pins. After setup according to the below diagram Bluetooth Module will start working. When you search for new Bluetooth it will appear as a other type of device.You can couple the device with your laptop using its embedded pin code. After that your PC will have a serial port open via Bluetooth. you can easily communicate with that.

  
  
  

Choosing suitable micro controller for Intelligent Traffic Light System

• Our first challenge was to find a suitable micro controller for this system. For this we consider following facts,
  
  • It have to control unknown number of lights belong to traffic lights. Most of the time it will more than 30.
  • It have to communicate with a laptop via Bluetooth or other wireless communication method.
  • It have to read unknown number of sensor values, most probably  less than 10.
  So considering above facts we choose the micro controller PIC 18f452 (http://www.microchip.com/wwwproducts/devices.aspx?ddocname=en010296) To fulfill the above aspects we have found some mechanisms.

Inteligent Traffic Ligth System

For the Semester 4 of the Computer Engineering Department of  University of Moratuwa, we learn a subject call Micro-Controllers and Applications. The aspect of this to learn the way of handling Micro-Controllers in their limited environment. For the project of this subject some of we have been asked to build a intelligent traffic light system.To describe it's functionality read this,

  

 

• Control of the road traffic on junctions :
  
  Up to maximum of 4 roads are intersecting with 4 pedestrians crossings in each road, near the junction. This will be the extreme, but system will be able to control all the other subset of junctions.
• Dynamic priority level for roads :
  
  This system will be able to sense all the vehicle movements through the junction.After sensing these movements, the system will adjust its timing parameters automatically to give the higher priority to roads which have much traffic level.
• Ability to configure system easily after installation:
  
  After installing the traffic light system in the roads, the configurations can be changed by plugging a simple interface to the system.
• Manual Override:
  
  When a Police Officer does traffic controlling, he will be able to control all the traffic lights using a remote control device.
• Fail Safe :
  
  If something goes wrong, the system should be able to move into state which will stop all the movements of vehicles and people, which will cause further damage.
• Energy Saving:
  Should be able to control the intensity of the lights in the night and day time.
• Automatic roll back to auto mood:
  
  If system has been changed to manual mood and if there are no commands issued to the system for a particular time period it switches back to auto mood.
• Can be configuring according to the place of installation:
  
  The abstract system is constructed to install in a junction which has 4 roads. But after doing few steps of configuration it can be used in any kind of place.

Our design was done based on the above functionality. I like to describe the steps we go through, First of all the below diagram shows our basic block diagram of the design.

• Further steps we have taken to develop the system will be given as following blog posts. Follow them to understand further.time.
  
  • http://obahamema.blogspot.com/2011/11/choosing-suitable-micro-controller-for.html
  • http://obahamema.blogspot.com/2011/11/choosing-suitable-wireless.html
  • http://obahamema.blogspot.com/2011/11/86-led-matrix-for-intelligent-traffic.html 
  • http://obahamema.blogspot.com/2011/11/inductive-loop-sensor-dynamic-traffic.html 
   
  

Useful Techniques in Assembly

How To Print Values Stored In Registers In Assembly

Most of the time when we use assembly, we load values to registers like AX,BX, Al,AH etc. Some time we need to print those values on the screen.

Before explain that we have to understand how the values are representing in the registers.

There are three type of representing values in a register,

1. Normal values(Pure decimal value convert in to binary and store in register)

For example, To store 68 we convert it to binary and its value is 1000100. So lets see the Value of each bit of AX register when we store that number in AX, AX is a 16bit register,

MSB 0000000001000100 LSB

2. As ASCII Values

For a Example Lets take we want to store "A8" in AX register; So the register saves the ASCII values in binary forum.

'A'=65=01000001

'8'=56=00111000

So the Values of AX Register is;

MSB 0011100001000001 LSB

3. Some Times We use Binary Coded Decimal To store VALUES.

0 = 0000

1 = 0001

2 = 0010

3 = 0011

4 = 0100

5 = 0101

6 = 0110

7 = 0111

8 = 1000

9 = 1001

So when we use to print a string stored in several registers as ASCII values we can use following technique to print values.

Varible_Name resd 16 ;Variable declaration in segment .bss section

mov [Varible_Name],eax ;move eax's four bytes to first 4 bytes of variable.

mov [Varible_Name],ebx ;move ebx's four bytes to first 4 bytes of variable.

mov [Varible_Name],ecx ;move ecx's four bytes to first 4 bytes of variable.

mov [Varible_Name],edx ;move edx's four bytes to first 4 bytes of variable.

mov si,Varible_Name

call _disp_str

_disp_str:

lodsb ; load next character

or al, al ; test for NUL character

jz .DONE

mov ah, 0x0E ; BIOS teletype

mov bh, 0x00 ; display page 0

mov bl, 0x07 ; text attribute

int 0x10 ; invoke BIOS

jmp _disp_str

.DONE:

ret

And when we want print a a 16bit value in binary in screen we have to move it to AX register and we can call this function. Then it will print the decimal value.

hex2dec:

push ax ; save that AX

push bx ; save that CX

push cx ; save that DX

push si ; save that SI

mov ax,dx ; copy number into AX

mov si,10 ; SI will be our divisor

xor cx,cx ; clean up the CX

non_zero:

xor dx,dx ; clean up the DX

div si ; divide by 10

push dx ; push number onto the stack

inc cx ; increment CX to do it more times

or ax,ax ; end of the number?

jne non_zero ; no? Keep chuggin' away

_write_digits:

pop dx ; get the digit off DX

add dl,48 ; add 48 to get ASCII

mov al, dl

mov ah, 0x0e

int 0x10

loop _write_digits

pop si ; restore that SI

pop cx ; restore that DX

pop bx ; restore that CX

pop ax ; restore that AX

ret ; End o' procedure!

X86 Assembly, if-else control Structures, loops

Comparisons

Control structures decide what to do based on comparisons of data. In assembly, the result of a comparison is stored in the FLAGS register to be38 . BASIC ASSEMBLY LANGUAGE used later. The 80x86 provides the CMP instruction to perform comparisons.The FLAGS register is set based on the difference of the two operands of the CMP instruction. The operands are subtracted and the FLAGS are set based on the result, but the result is not stored anywhere. If you need the result use the SUB instead of the CMP instruction.For unsigned integers, there are two flags (bits in the FLAGS register) that are important: the zero (ZF) and carry (CF) flags. The zero flag is set (1) if the resulting difference would be zero. The carry flag is used as a borrow flag for subtraction. Consider a comparison like:

cmp vleft, vright

The difference of vleft - vright is computed and the flags are set accord-ingly. If the difference of the of CMP is zero, vleft = vright, then ZF is set (i.e. 1) and the CF is unset (i.e. 0). If vleft > vright, then ZF is unset and CF is unset (no borrow). If vleft <>

is set (borrow).For signed integers, there are three flags that are important: the zero

(ZF) flag, the overflow (OF) flag and the sign (SF) flag. The overflow flag Why does SF = OF if

vleft > vright? If there is no overflow, then the difference will have the correct value and must

be non-negative. Thus,SF = OF = 0. However,if there is an overflow, the difference will not have the correct value (and in fact will be negative). Thus,SF = OF = 1.is set if the result of an operation overflows (or underflows). The sign flag is set if the result of an operation is negative. If vleft = vright, the ZF is set (just as for unsigned integers). If vleft > vright, ZF is unset and

SF = OF. If vleft < sf =" OF.">

Branch instructions

Branch instructions can transfer execution to arbitrary points of a program. In other words, they act like a goto. There are two types of branches:unconditional and conditional. An unconditional branch is just like a goto,it always makes the branch. A conditional branch may or may not make the branch depending on the flags in the FLAGS register. If a conditional branch does not make the branch, control passes to the next instruction. The JMP (short for jump) instruction makes unconditional branches. Its single argument is usually a code label to the instruction to branch to. The assembler or linker will replace the label with correct address of the instruction. This is another one of the tedious operations that the assembler does to make the programmer’s life easier. It is important to realize that the statement immediately after the JMP instruction will never be executed unless another instruction branches to it!

Simple Conditional Branches

JZ branches only if ZF is set

JNZ branches only if ZF is unset

JO branches only if OF is set

JNO branches only if OF is unset

JS branches only if SF is set

JNS branches only if SF is unset

JC branches only if CF is set

JNC branches only if CF is unset

JP branches only if PF is set

JNP branches only if PF is unset

There are several variations of the jump instruction: SHORT This jump is very limited in range. It can only move up or down 128 bytes in memory. The advantage of this type is that it uses less

memory than the others. It uses a single signed byte to store the displacement of the jump. The displacement is how many bytes to move ahead or behind. (The displacement is added to EIP). To specify a short jump, use the SHORT keyword immediately before the label in the JMP instruction.

NEAR This jump is the default type for both unconditional and conditional branches, it can be used to jump to any location in a segment. Actually, the 80386 supports two types of near jumps. One uses two bytes for the displacement. This allows one to move up or down roughly 32,000 bytes. The other type uses four bytes for the displacement, which of course allows one to move to any location in the code segment. The four byte type is the default in 386 protected mode. The two byte type can be specified by putting the WORD keyword

before the label in the JMP instruction.

FAR This jump allows control to move to another code segment. This is a very rare thing to do in 386 protected mode. Valid code labels follow the same rules as data labels. Code labels are defined by placing them in the code segment in front of the statement they label. A colon is placed at the end of the label at its point of definition. The

colon is not part of the name.

There are many different conditional branch instructions. They also take a code label as their single operand. The simplest ones just look at a single flag in the FLAGS register to determine whether to branch or not.See Table for a list of these instructions. (PF is the parity flag which

indicates the odd or evenness of the number of bits set in the lower 8-bits of the result.)

The following pseudo-code,

if ( EAX == 0 )

EBX = 1;

else

EBX = 2;

could be written in assembly as:

1 cmp eax, 0 ; set flags (ZF set if eax - 0 = 0)

2 jz thenblock ; if ZF is set branch to thenblock

3 mov ebx, 2 ; ELSE part of IF

4 jmp next ; jump over THEN part of IF

5 thenblock:

6 mov ebx, 1 ; THEN part of IF

7 next:

Other comparisons are not so easy using the conditional branches in Table To illustrate, consider the following pseudo-code:

if ( EAX >= 5 )

EBX = 1;

else

EBX = 2;

If EAX is greater than or equal to five, the ZF may be set or unset and SF will equal OF. Here is assembly code that tests for these conditions (assuming that EAX is signed):

1 cmp eax, 5

2 js signon ; goto signon if SF = 1

3 jo elseblock ; goto elseblock if OF = 1 and SF = 0

4 jmp thenblock ; goto thenblock if SF = 0 and OF = 0

5 signon:

6 jo thenblock ; goto thenblock if SF = 1 and OF = 1

7 elseblock:

8 mov ebx, 2

9 jmp next

10 thenblock:

11 mov ebx, 1

12 next:

The above code is very awkward. Fortunately, the 80x86 provides additional branch instructions to make these type of tests much easier. There are signed and unsigned versions of each. Table shows these instructions. The equal and not equal branches (JE and JNE) are the same for both signed and unsigned integers. (In fact, JE and JNE are really identical2.2.

Signed and Unsigned Comparison Instructions

JE branches if vleft = vright JE branches if vleft = vright

JNE branches if vleft = vright JNE branches if vleft = vright

JL, JNGE branches if vleft <>

JLE, JNG branches if vleft ≤ vright JBE, JNA branches if vleft ≤ vright

JG, JNLE branches if vleft > vright JA, JNBE branches if vleft > vright

JGE, JNL branches if vleft ≥ vright JAE, JNB branches if vleft ≥ vright

Signed Unsigned to JZ and JNZ, respectively.) Each of the other branch instructions have

two synonyms. For example, look at JL (jump less than) and JNGE (jump not greater than or equal to). These are the same instruction because: x < y ="⇒">

1 cmp eax, 5

2 jge thenblock

3 mov ebx, 2

4 jmp next

5 thenblock:

6 mov ebx, 1

7 next:

The loop instructions

The 80x86 provides several instructions designed to implement for -like loops. Each of these instructions takes a code label as its single operand. LOOP Decrements ECX, if ECX = 0, branches to label LOOPE, LOOPZ Decrements ECX (FLAGS register is not modified), if

ECX = 0 and ZF = 1, branches LOOPNE, LOOPNZ Decrements ECX (FLAGS unchanged), if ECX = 0 and ZF = 0, branches

The last two loop instructions are useful for sequential search loops.

The following pseudo-code:

sum = 0;

for ( i=10; i >0; i−− )

sum += i;

could be translated into assembly as:

1 mov eax, 0 ; eax is sum

2 mov ecx, 10 ; ecx is i

3 loop_start:

4 add eax, ecx

5 loop loop_start

Translating Standard Control Structures

This section looks at how the standard control structures of high level languages can be implemented in assembly language.

If statements

The following pseudo-code:

if ( condition )

then block ;

else

else block ;

could be implemented as:

1 ; code to set FLAGS

2 jxx else_block ; select xx so that branches if condition false

3 ; code for then block

4 jmp endif

5 else_block:

6 ; code for else block

7 endif:

If there is no else, then the else block branch can be replaced by a

branch to end if.

1 ; code to set FLAGS

2 jxx endif ; select xx so that branches if condition false

3 ; code for then block

4 endif

While loops

The while loop is a top tested loop:

while( condition ) {

body of loop;

}

This could be translated into:

1 while:

2 ; code to set FLAGS based on condition

3 jxx endwhile ; select xx so that branches if false

4 ; body of loop

5 jmp while

6 endwhile:

Do while loops

The do while loop is a bottom tested loop:

do {

body of loop;

} while( condition );

This could be translated into:

1 do:

2 ; body of loop

3 ; code to set FLAGS based on condition

4 jxx do ; select xx so that branches if true

Refrence - PC Assembly Language Paul A. Carter

BIOS Interrupt Calls To get Hardware and Other Data

BIOS Interrupt Calls.

Interrupt calls are a functionality provided by BIOS to get particular data from system and save them in the Registers of the CPU. (See The Appendix to find out what are x86 registers.) They invoked in particular way,

int inturrptVecotr in hex

From this manner we can call a particular interrupt and retrieve values from system. The manufactures provide a documentation of interrupt Vectors. They specify which interrupt can return which values. There are so many conditions and those conditions gives different information. The complete description of the interrupt vectors are giving in below reference's.

http://en.wikipedia.org/wiki/BIOS_interrupt_call

http://iwsm2004.cs.uni-magdeburg.de/~zbrog/asm/interrupt.html

http://www.ctyme.com/rbrown.htm

How To Find Your Processor Brand String

CPUID function in x86 Assembly Language

CPUID is an instruction provided by processor manufacture, it is an Assembly instruction. It has no operands in its function call. But it takes arguments from AX register. It provides processor identification information in registers EAX, EBX, ECX, and EDX. This information identifies Intel as the vendor, gives the family, model, and stepping of processor, feature information, and cache information. An input value loaded into the EAX register determines what information is returned. There is list of AX register values which retunes different information about CPU.

• EAX=0h, CPUID

This returns the CPU's manufacturer ID string - a twelve character ASCII string stored in EBX, EDX, ECX - in that order. The highest basic calling parameter is returned in EAX. EBX, EDX, ECX, EAX are 32bit registers. We can store 4 8bit characters. Here is a example values of registers after CPUID call.

EAX= Maximum Input Value for Basic CPUID Information (see second table)

EBX= "Genu"

ECX= "ntel"

EDX= "ineI"

• EAX=80000002h,80000003h,80000004h, CPUID

These return the processor brand string in EAX, EBX, ECX and EDX. CPUID must be issued with each parameter in sequence to get the entire 48-byte null-

terminated ASCII processor brand string.

EAX=80000002h;

EAX=” ”

EBX=” ”

ECX=” “

EDX= "nI "

EAX=80000003h;

EAX= "(let"

EBX= "P )R"

ECX= "itne"

EDX= "R(mu"

EAX=80000003h;

EAX= " 4 )"

EBX= " UPC"

ECX= "0051"

EDX= "zHM"

Hear also you have to write assembly codes to set AX value and call CPUID and extract data from registers and print them. Do it iteratively four times to get the processor brand string.

Find Hardware info_Do You Know How Drivers are searched through Internet

Finding About Your Hardware Details.

This is the slandered way of finding hardware details ..

Evey hardware has a thing called Hardware ID it has two Portions, one is Vendor ID and Device ID.

When you find these two you can easily find out every thing about your hardware.

This not need any kind of drivers.

You can search through sites like this for your informations.

http://www.pcidatabase.com/

In Windows You can find Your Hardware ID This way......

1. Open Device Manager (Control Panel>System>Hardware>Device Manager)
2. The hardware whose drivers are missing will appear as Unknown device, so it's easier to locate the device.
3. Right click on the unknown device and click on Properties.
4. Under the Properties window click on Details tab and select Device Instance Id from the drop down box.
5. You should see a code similar to this
   
   PCI\VEN_8086&DEV_27DC&SUBSYS_30868086
   &REV_01\4&1E46F438&0&40F0
6. The portion of the code after VEN is the Vendor ID and the portion after DEV is the Device ID. In this example:
   
   Vendor ID = 8086
   Device ID = 27DC

In Linux you can use

dmidecode | more and man dmidecode for more information

SMBIOS - Gives Hardware Specifications

System Management BIOS (SMBIOS)

The SMBIOS provides numerous tables of data describing a computer's configuration. Available information includes items such as vendor name, BIOS version, installed components, CPU clock speed, etc.

The functions given in this section can be used to retrieve and parse the SMBIOS tables. Declarations of these functions and table entries (structures) are available in file Include\Rttsmbios.h and Libdel\Rttsmbios.pas.

Types RTSMSTR, RTSTRCNT, and RTSMHNDL used in some of the SMBIOS structures have special semantics. Values of type RTSMSTR are string indices. Function RTSMBIOSGetString can retrieve a pointer to the associated string. Values of type RTSTRCNT denote how many strings are appended to a structure. FunctionRTSMBIOSGetStringN can retrieve all such strings. Values of type RTSMHNDL reference another SMBIOS structure which can be located with RTSMBIOSFindHandle.

The SMBIOS structure declarations included in the following sections and in file Include\Rttsmbios.h correspond to version 2.4 of the SMBIOS specification. Older SMBIOS versions may only support a subset of the declared structure fields as later SMBIOS versions have appended data members to some structures. FunctionRTSMBIOSIsValid may be used to check if a particular structure member is supported.

We can find Following things using SMBIOS

0 BIOS
1 System
2 Base Board
3 Chassis
4 Processor
5 Memory Controller
6 Memory Module
7 Cache
8 Port Connector
9 System Slots
10 On Board Devices
11 OEM Strings
12 System Configuration Options
13 BIOS Language
14 Group Associations
15 System Event Log
16 Physical Memory Array
17 Memory Device
18 32-bit Memory Error
19 Memory Array Mapped Address
20 Memory Device Mapped Address
21 Built-in Pointing Device
22 Portable Battery
23 System Reset
24 Hardware Security
25 System Power Controls
26 Voltage Probe
27 Cooling Device
28 Temperature Probe
29 Electrical Current Probe
30 Out-of-band Remote Access
31 Boot Integrity Services
32 System Boot
33 64-bit Memory Error
34 Management Device
35 Management Device Component
36 Management Device Threshold Data
37 Memory Channel
38 IPMI Device
39 Power Supply

For How To do it?

http://code.google.com/p/open-hardware-monitor/source/browse/trunk/Hardware/Mainboard/SMBIOS.cs?r=179

But i am working on a solution in C or x86 ASM