VGA doesn't print

[shervingav]

ok, so i coded my semi-working os with getting help from bare bones and Brandon F. 's kernel tutorial and i have a little problem,
my problem is that when i run my kernel.iso (in qemu) the os is supposed to clear the screen and print the char 'C' to the screen on 0xb8000,
but when i run it, nothing happens and i have a blinking cursor, and when i hold Alt+Ctrl+2 and when i type xp from 0xb8000 to 0xb8009
i see the following:

Code: Select all

xp 0xb8000 
00000000000b8000: 0x07200720
xp 0xb8001 
00000000000b8001: 0x20072007
xp 0xb8002 
00000000000b8002: 0x07200720
xp 0xb8003 
00000000000b8003: 0x20072007
xp 0xb8004 
00000000000b8004: 0x07200720
xp 0xb8005 
00000000000b8005: 0x20072007
xp 0xb8006 
00000000000b8006: 0x07200720
xp 0xb8007 
00000000000b8007: 0x20072007
xp 0xb8008
00000000000b8008: 0x07200720
xp 0xb8009 
00000000000b8009: 0x20072007

and after a minute or so when i check them again, all of them are set to 0.
these are the code i use for vga:

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void kmain(void)
{
	init_video();
	putch('C');
        for (;;);
}

and this is my vga structure:

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struct {
	uint16 *textmemptr;
	uint16 attrib;
	uint16 csr_x ,csr_y;
}VGA;

and these are my putch() and init_video() functions

Code: Select all

void scroll()
{
    uint16 blank, temp;
    blank = 0x20 | (VGA.attrib << 8);
    if(VGA.csr_y >= 25)
    {
        temp = VGA.csr_y - 25 + 1;
        memcpyw (VGA.textmemptr, VGA.textmemptr + temp * 80, (25 - temp) * 80 * 2);
        memsetw (VGA.textmemptr + (25 - temp) * 80, blank, 80);
        VGA.csr_y = 25 - 1;
    }
}
void move_csr()
{
    uint8 temp;
    temp = VGA.csr_y * 80 + VGA.csr_x;
    outportb(0x3D4, 14);
    outportb(0x3D5, temp >> 8);
    outportb(0x3D4, 15);
    outportb(0x3D5, temp);
}

void cls()
{
    uint16 blank;
    int i;
    blank = 0x20 | (VGA.attrib << 8);
    for(i = 0; i < 25; i++)
        memsetw (VGA.textmemptr + i * 80, blank, 80);
    VGA.csr_x = 0;
    VGA.csr_y = 0;
    move_csr();
}

void putch(uint8 c)
{
    uint16 *where;
    uint16 att = VGA.attrib << 8;
    if(c == 0x08)
    {
        if(VGA.csr_x != 0) VGA.csr_x--;
    }
    else if(c == 0x09)
    {
        VGA.csr_x = (VGA.csr_x + 8) & ~(8 - 1);
    }
    else if(c == '\r')
    {
        VGA.csr_x = 0;
    }
    else if(c == '\n')
    {
        VGA.csr_x = 0;
        VGA.csr_y++;
    }
    else if(c >= ' ')
    {
        where = VGA.textmemptr + (VGA.csr_y * 80 + VGA.csr_x);
        *where = c | att;
        VGA.csr_x++;
    }
    if(VGA.csr_x >= 80)
    {
        VGA.csr_x = 0;
        VGA.csr_y++;
    }

    scroll();
    move_csr();
}
void init_video()
{
    VGA.textmemptr = (uint16 *)0xb8000;
    VGA.attrib = 0x0F;
	VGA.csr_x = 0;
	VGA.csr_y = 0;
	cls();
}

[ScropTheOSAdventurer]

A disassembly of your putch function could be helpful. In addition, could you provide your mem* functions? Your letters might be getting erased by a mem* function being bad.

[no92]

Looks okay for me, do you get any warnings thrown by gcc/clang?

BTW, there's no need in looping in the main C sources, as this is done by assembly:

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jmp $

[shervingav]

A disassembly of your putch function could be helpful. In addition, could you provide your mem* functions? Your letters might be getting erased by a mem* function being bad.

ok my mem functions are as follows:

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uint8 *memcpy(uint8 *dest, const uint8 *src, int count)
{
    int i = 0;
start_cpy:
    *(dest+i) = *(src+i);
    i = i + 1;
    if (i < count)
       goto start_cpy;
    return dest;
}
uint16 *memcpyw(uint16 *dest, const uint16 *src, int count)
{
    int i = 0;
start_cpy1:
    *(dest+i) = *(src+i);
    i = i + 1;
    if (i < count)
       goto start_cpy1;
    return dest;
}

uint8 *memset(uint8 *dest, uint8 val, int count)
{
    int i = 0;
start_set:
    *(dest+i) = val;
    i = i + 1;
    if (i < count)
	goto start_set;
    return dest;
}

uint16 *memsetw(uint16 *dest, uint16 val, int count)
{
    int i = 0;
start_set1:
    dest[i] = val;
    i = i + 1;
    if (i < count)
	goto start_set1;
    return dest;
}

A disassembly of your putch function could be helpful.

I am a beginner and i dont know how to disassmble my putch func + what does disassemble mean?? reversing the code from bin to asm??

Looks okay for me, do you get any warnings thrown by gcc/clang?

no i dont.

[shervingav]

I have encountered another problem:
in start.asm there was this code(just a part of it):

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global _start
_start:
    mov esp, _sys_stack
	mov dx,0x3c0 ;for setting the text mode : 80x25
	mov al,0x10 ;for setting the text mode : 80x25
	out dx,al ;for setting the text mode : 80x25
	mov al,0x0c ;for setting the text mode : 80x25
	out dx,al ;for setting the text mode : 80x25
    jmp stublet

and when i removed the part for setting the text mode my os just crashes!! why??

[shervingav]

HAHAHAHAHHAHAHAHAHA!
i solved it. my file architectures where not right my nasm was 64 bit and that messed up my kernel.
ty all.