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; bkerndev - Bran's Kernel Development Tutorial
; By:   Brandon F. ([email protected])
; Desc: Kernel entry point, stack, and Interrupt Service Routines.
;
; Notes: No warranty expressed or implied. Use at own risk.
;
; This is the kernel's entry point. We could either call main here,
; or we can use this to setup the stack or other nice stuff, like
; perhaps setting up the GDT and segments. Please note that interrupts
; are disabled at this point: More on interrupts later!
[BITS 32]
global start
start:
    mov esp, _sys_stack     ; This points the stack to our new stack area
    jmp stublet

; This part MUST be 4byte aligned, so we solve that issue using 'ALIGN 4'
ALIGN 4
mboot:
    ; Multiboot macros to make a few lines later more readable
    MULTIBOOT_PAGE_ALIGN	equ 1<<0
    MULTIBOOT_MEMORY_INFO	equ 1<<1
    MULTIBOOT_AOUT_KLUDGE	equ 1<<16
    MULTIBOOT_HEADER_MAGIC	equ 0x1BADB002
    MULTIBOOT_HEADER_FLAGS	equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE
    MULTIBOOT_CHECKSUM	equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
    EXTERN code, bss, end

    ; This is the GRUB Multiboot header. A boot signature
    dd MULTIBOOT_HEADER_MAGIC
    dd MULTIBOOT_HEADER_FLAGS
    dd MULTIBOOT_CHECKSUM
    
    ; AOUT kludge - must be physical addresses. Make a note of these:
    ; The linker script fills in the data for these ones!
    dd mboot
    dd code
    dd bss
    dd end
    dd start

; This is an endless loop here. Make a note of this: Later on, we
; will insert an 'extern _main', followed by 'call _main', right
; before the 'jmp $'.
stublet:
    extern main
    call main
    jmp $


; Shortly we will add code for loading the GDT right here!


; In just a few pages in this tutorial, we will add our Interrupt
; Service Routines (ISRs) right here!



; Here is the definition of our BSS section. Right now, we'll use
; it just to store the stack. Remember that a stack actually grows
; downwards, so we declare the size of the data before declaring
; the identifier '_sys_stack'
SECTION .bss
    resb 8192               ; This reserves 8KBytes of memory here
_sys_stack:

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#ifndef __SYSTEM_H
#define __SYSTEM_H
#define size_t int /*Now this is because of the prototypes i got from the website i mentioned...is it correct?*/
/* MAIN.C */
extern void *memcpy(void *dest, const void *src, size_t count);
extern void *memset(void *dest, char val, size_t count);
extern unsigned short *memsetw(unsigned short *dest, unsigned short val, size_t count);
extern size_t strlen(const char *str);
extern unsigned char inportb (unsigned short _port);
extern void outportb (unsigned short _port, unsigned char _data);
/* SCRN.C */
extern void cls();
extern void putch(unsigned char c);
extern void puts(unsigned char *str);
extern void settextcolor(unsigned char forecolor, unsigned char backcolor);
extern void init_video();
#endif

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#include <system.h>
/* You will need to code these up yourself!  */

/*void *memcpy(void *dest, const void *src, int count)

{

    const char *sp = (const char *)src;

    char *dp = (char *)dest;

    for(; count != 0; count--) *dp++ = *sp++;

    return dest;

}



void *memset(void *dest, char val, int count)

{

    char *temp = (char *)dest;

    for( ; count != 0; count--) *temp++ = val;

    return dest;

}



unsigned short *memsetw(unsigned short *dest, unsigned short val, int count)

{

    unsigned short *temp = (unsigned short *)dest;

    for( ; count != 0; count--) *temp++ = val;

    return dest;

}



int strlen(const char *str)

{

	const char * q = str;

	while (* q++);

		return (q-str+1);

}*/

void *memcpy(void *dest, const void *src, size_t count)
{
    const char *sp = (const char *)src;
    char *dp = (char *)dest;
    for(; count != 0; count--) *dp++ = *sp++;
    return dest;
}

void *memset(void *dest, char val, size_t count)
{
    char *temp = (char *)dest;
    for( ; count != 0; count--) *temp++ = val;
    return dest;
}

unsigned short *memsetw(unsigned short *dest, unsigned short val, size_t count)
{
    unsigned short *temp = (unsigned short *)dest;
    for( ; count != 0; count--) *temp++ = val;
    return dest;
}

size_t strlen(const char *str)
{
    size_t retval;
    for(retval = 0; *str != '\0'; str++) retval++;
    return retval;
}

/* We will use this later on for reading from the I/O ports to get data
*  from devices such as the keyboard. We are using what is called
*  'inline assembly' in these routines to actually do the work */
unsigned char inportb (unsigned short _port)
{
    unsigned char rv;
    __asm__ __volatile__ ("inb %1, %0" : "=a" (rv) : "dN" (_port));
    return rv;
}

/* We will use this to write to I/O ports to send bytes to devices. This
*  will be used in the next tutorial for changing the textmode cursor
*  position. Again, we use some inline assembly for the stuff that simply
*  cannot be done in C */
void outportb (unsigned short _port, unsigned char _data)
{
    __asm__ __volatile__ ("outb %1, %0" : : "dN" (_port), "a" (_data));
}

/* This is a very simple main() function. All it does is sit in an
*  infinite loop. This will be like our 'idle' loop */
void main()
{
    /* You would add commands after here */
    init_video();
    puts("Hello World");
    /* ...and leave this loop in. There is an endless loop in
    *  'start.asm' also, if you accidentally delete this next line */
    for (;;);
}

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/* bkerndev - Bran's Kernel Development Tutorial
*  By:   Brandon F. ([email protected])
*  Desc: Screen output functions for Console I/O
*
*  Notes: No warranty expressed or implied. Use at own risk. */
#include <system.h>

/* These define our textpointer, our background and foreground
*  colors (attributes), and x and y cursor coordinates */
unsigned short *textmemptr;
int attrib = 0x0F;
int csr_x = 0, csr_y = 0;

/* Scrolls the screen */
void scroll(void)
{
    unsigned blank, temp;

    /* A blank is defined as a space... we need to give it
    *  backcolor too */
    blank = 0x20 | (attrib << 8);

    /* Row 25 is the end, this means we need to scroll up */
    if(csr_y >= 25)
    {
        /* Move the current text chunk that makes up the screen
        *  back in the buffer by a line */
        temp = csr_y - 25 + 1;
        memcpy (textmemptr, textmemptr + temp * 80, (25 - temp) * 80 * 2);

        /* Finally, we set the chunk of memory that occupies
        *  the last line of text to our 'blank' character */
        memsetw (textmemptr + (25 - temp) * 80, blank, 80);
        csr_y = 25 - 1;
    }
}

/* Updates the hardware cursor: the little blinking line
*  on the screen under the last character pressed! */
void move_csr(void)
{
    unsigned temp;

    /* The equation for finding the index in a linear
    *  chunk of memory can be represented by:
    *  Index = [(y * width) + x] */
    temp = csr_y * 80 + csr_x;

    /* This sends a command to indicies 14 and 15 in the
    *  CRT Control Register of the VGA controller. These
    *  are the high and low bytes of the index that show
    *  where the hardware cursor is to be 'blinking'. To
    *  learn more, you should look up some VGA specific
    *  programming documents. A great start to graphics:
    *  http://www.brackeen.com/home/vga */
    outportb(0x3D4, 14);
    outportb(0x3D5, temp >> 8);
    outportb(0x3D4, 15);
    outportb(0x3D5, temp);
}

/* Clears the screen */
void cls()
{
    unsigned blank;
    int i;

    /* Again, we need the 'short' that will be used to
    *  represent a space with color */
    blank = 0x20 | (attrib << 8);

    /* Sets the entire screen to spaces in our current
    *  color */
    for(i = 0; i < 25; i++)
        memsetw (textmemptr + i * 80, blank, 80);

    /* Update out virtual cursor, and then move the
    *  hardware cursor */
    csr_x = 0;
    csr_y = 0;
    move_csr();
}

/* Puts a single character on the screen */
void putch(unsigned char c)
{
    unsigned short *where;
    unsigned att = attrib << 8;

    /* Handle a backspace, by moving the cursor back one space */
    if(c == 0x08)
    {
        if(csr_x != 0) csr_x--;
    }
    /* Handles a tab by incrementing the cursor's x, but only
    *  to a point that will make it divisible by 8 */
    else if(c == 0x09)
    {
        csr_x = (csr_x + 8) & ~(8 - 1);
    }
    /* Handles a 'Carriage Return', which simply brings the
    *  cursor back to the margin */
    else if(c == '\r')
    {
        csr_x = 0;
    }
    /* We handle our newlines the way DOS and the BIOS do: we
    *  treat it as if a 'CR' was also there, so we bring the
    *  cursor to the margin and we increment the 'y' value */
    else if(c == '\n')
    {
        csr_x = 0;
        csr_y++;
    }
    /* Any character greater than and including a space, is a
    *  printable character. The equation for finding the index
    *  in a linear chunk of memory can be represented by:
    *  Index = [(y * width) + x] */
    else if(c >= ' ')
    {
        where = textmemptr + (csr_y * 80 + csr_x);
        *where = c | att;	/* Character AND attributes: color */
        csr_x++;
    }

    /* If the cursor has reached the edge of the screen's width, we
    *  insert a new line in there */
    if(csr_x >= 80)
    {
        csr_x = 0;
        csr_y++;
    }

    /* Scroll the screen if needed, and finally move the cursor */
    scroll();
    move_csr();
}

/* Uses the above routine to output a string... */
void puts(unsigned char *text)
{
    int i;

    for (i = 0; i < strlen(text); i++)
    {
        putch(text[i]);
    }
}

/* Sets the forecolor and backcolor that we will use */
void settextcolor(unsigned char forecolor, unsigned char backcolor)
{
    /* Top 4 bytes are the background, bottom 4 bytes
    *  are the foreground color */
    attrib = (backcolor << 4) | (forecolor & 0x0F);
}

/* Sets our text-mode VGA pointer, then clears the screen for us */
void init_video(void)
{
    textmemptr = (unsigned short *)0xB8000;
    cls();
}

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OUTPUT_FORMAT("binary")
ENTRY(start)
phys = 0x00100000;
SECTIONS
{
  .text phys : AT(phys) {
    code = .;
    *(.text)
    *(.rodata)
    . = ALIGN(4096);
  }
  .data : AT(phys + (data - code))
  {
    data = .;
    *(.data)
    . = ALIGN(4096);
  }
  .bss : AT(phys + (bss - code))
  {
    bss = .;
    *(.bss)
    . = ALIGN(4096);
  }
  end = .;
}

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echo Now assembling, compiling, and linking your kernel:
echo NASM is assembling...
echo start.asm...
nasm -f aout -o start.o start.asm
#echo start.asm...done
#Remember this spot here: We will add 'gcc' commands here to compile C sources
#echo GCC is compiling...
echo main.c...
gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o main.o main.c
echo main.c...done
echo scrn.c...
gcc -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -I./include -c -o scrn.o scrn.c
echo scrn.c...done
#This links all your files. Remember that as you add *.o files, you need to
#add them after start.o. If you don't add them at all, they won't be in your kernel!
echo LD is linking...
ld -T link.ld -o kernel.bin start.o scrn.o main.o
echo Now copying kernel.bin to floppy0, plese make sure this device is mounted...
cp kernel.bin /media/floppy0/
echo Done!

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Kernel... OK
Protected Mode... OK
Setting up interupts... OK
Setting up keyboard... OK
Starting kernel thread... Welcome to kernel thread!
@: _