I/O functions

[p0s1x]

Hello world, I have a question, how to make basic printf or scanf functions on OS?
I use this:

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void write_string( int colour, const char *string )
{
    volatile char *video = (volatile char*)0xB8000;
    while( *string != 0 )
    {
        *video++ = *string++;
        *video++ = colour;
    }
};

but this can't print any string or character. Console pointer goes crazy. Can you help? Thanks.

//Sorry for bad English

[MDenham]

Are you sure you're operating in real mode when this function is called?

[p0s1x]

Are you sure you're operating in real mode when this function is called?

I use bare bones from here. I not sure.

[p0s1x]

I use this (My code :3):

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void printf(char *string )
{
	asm( 
   "mov %si, string          \n"
   "call DisplayMessage    \n"
   "DisplayMessage:        \n"
   "lodsb                       \n"
   "or   %al, %al             \n"
   "jz   .DONE                 \n"
   "mov   %ah, 0x0E        \n"
   "mov   %bh, 0x00        \n"
   "mov   %bl, 0x07         \n"
   "int   $0x10                \n"
   "jmp   DisplayMessage  \n"
   ".DONE:                     \n"
   "ret                           \n");
};

And have linker error:

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kernel.o:kernel.c:(.text+0x40): undefined reference to `string'

How to use C variables in inline assembler?

[bluemoon]

If you follow the bare bone tutorial, I assume you're on gcc.
inline assembly with gcc uses input/output/clobber lists instead of putting variable names directly in assembly instruction (aka old visual c++ style), I suggest you read the gcc inline assembly manual.

By the way, string is a really bad variable name.

[Gigasoft]

If your GCC program is running, then the processor must not be in real mode. Otherwise, you would not be able to run your program. Therefore, you can not call BIOS functions.

[iansjack]

In your original program you are assuming that

char *video = (volatile char*)0xB8000;

points to video memory. I'd say that is quite a large assumption; it may depend upon what value you have placed in DS.

[p0s1x]

How to move CPU in Real Time Mode?

[Brendan]

Hi,

How to move CPU in Real Time Mode?

Do you mean: How do you move data (using the CPU) while in Real Mode?

If this is what you're asking, then my favourite is "rep movsd".


Cheers,

Brendan

[p0s1x]

Bare Bones switch CPU to Real or Protected mode?

[Mikemk]

Bare Bones switch CPU to Real or Protected mode?

You want to switch from real mode to pmode, then immediately back to real mode?

[p0s1x]

I want to switch CPU to protected mode for access video memory

[Mikemk]

Here is a code sample. Let's see if you can implement it.
BTW, I don't know c++, so you or somebody will have to translate.
From real mode (assuming string index passed in ds:si, and color in al):

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print:
mov bx, 0xb800
mov es, bx
xor bx, bx
.loop:
mov ah, [si]
cmp ah, 0
je .endi
mov [es:bx], ax
add bx, 2
inc si
jmp .loop
.endi:

pmode:

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print:
mov bx, [i]selector[/i]
mov es, bx
mov ebx, 0xb8000
.loop:
mov ah, [esi]
cmp ah, 0
je .endi
mov [es:ebx], ax
add ebx, 2
inc esi
jmp .loop
.endi:

[p0s1x]

My friend send me code:

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sysenter

"That code enter system to pmode", really?

[Nessphoro]

My friend send me code:

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sysenter

"That code enter system to pmode", really?