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Posted: **Sun Feb 03, 2008 3:19 am**

Hello, I am working on remapping pic and I am having some unknown problems with my C code. Right now the program displays a message once main has been given control.

Code: Select all

void main()
{
cls(0x07);
printf(0x07, "Hello",1,1);
for(;;);
}

Whenever I add this code:

Code: Select all

void remap_pics()
{
	/* send ICW1 */
	out(0x20,  0x11);
	out(0xA0,  0x11);

	/* send ICW2 */
	out(0x20 + 1, 0x20);	//master
	out(0xA0 + 1, 0x28);	//slave

	/* send ICW3 */
	out(0x20 + 1, 4);
	out(0xA0 + 1, 2);

	/* send ICW4 */
	out(0x20 + 1, 0x01);
	out(0xA0 + 1, 0x01);

	/* disable all IRQs */
	out(0x20 + 1, 0xFF);
}

to my video.c source:

Code: Select all

//***********************
// Function: Clear the Screen
// Equivalent: cls();
//***********************

void cls(int color) 
{
  char *vga = (char *) 0xb8000;
  unsigned int i=0;
  while(i < (80*25*2))
  {
      vga[i]=' ';
      i++;
      vga[i]=color;
      i++;
  }
}

//*****************************
// Function: Print Formatted Strings
// Equivalent: printf();
//*****************************

void printf(unsigned char color, char *string, int x, int y)
{
  char *vga = (char *) 0xb8000;
  unsigned int i = 160*y + 2*x;
  while (*string)
  {
	switch(*string)
	{
		case '\n': //newline
		y++;
		i = 160*y + 2*x;
		*string++;
		break;
	}
	//print formatted string
	vga[i++] = *string++;
	vga[i++] = color;
  }
}

My program prints out garbage on the screen instead of the intended message; even without calling the function remap_pics();. When I do call it:

Code: Select all

void main()
{
cls(0x07);
printf(0x07, "Hello",1,1);
remap_pics();
for(;;);
}

The system crashes.

My out() and in() functions are both in my ports.c source:

Code: Select all

unsigned char in(unsigned short _port) //input a byte
{
  // "=a" (result) means: put AL register in variable result when finished
  // "d" (_port) means: load EDX with _port
  unsigned char result;
  __asm__ __volatile__("in %%dx, %%al" : "=a" (result) : "d" (_port));
  return result;
}

void out(unsigned short _port, unsigned char _data) //output a byte to a port
{
  // "a" (_data) means: load EAX with _data
  // "d" (_port) means: load EDX with _port
  __asm__ __volatile__("out %%al, %%dx" : :"a" (_data), "d" (_port));
}

Any help?

Posted: **Sun Feb 03, 2008 4:12 am**

Are you loading a fixed amount of disk sectors?

Posted: **Sun Feb 03, 2008 4:18 am**

Code: Select all

reset_drive:
        mov ah, 0               ; RESET-command
        int 13h                 ; Call interrupt 13h
        or ah, ah               ; Check for error code
        jnz reset_drive         ; Try again if ah != 0

        mov ax, 0
        mov es, ax
        mov bx, 0x1000          ; We load our code at offset: 0:1000h

        mov ah, 02h             ; READ SECTOR-command
        mov al, 02h             ; Number of sectors to read = 1
        mov ch, 0               ; Cylinder = 0
        mov cl, 02h             ; Sector = 2
        mov dh, 0               ; Head = 0
        int 13h                 ; Call interrupt 13h
        or ah, ah               ; Check for error code
        jnz reset_drive         ; Try again if ah != 0

Posted: **Sun Feb 03, 2008 4:26 am**

does that mean that you load 512 bytes from the floppy when your kernel is by far larger than that?

Posted: **Sun Feb 03, 2008 4:28 am**

It must. What should I do?

Posted: **Sun Feb 03, 2008 4:36 am**

eeeeeeeeeh, load more sectors than just one?

Seriously, your intelligence level seems to hit an all time low at this point, even though I have the idea that you are far more capable than this. I suggest you read http://catb.org/~esr/faqs/smart-questions.html - it at least helps in not making more of a fool from yourself.

Posted: **Sun Feb 03, 2008 1:43 pm**

It was late and I thought you might say something like that.. haha. I should have said How should I do that? So, just add more sectors and that is it?

Code: Select all

reset_drive:
        mov ah, 0               ; RESET-command
        int 13h                 ; Call interrupt 13h
        or ah, ah               ; Check for error code
        jnz reset_drive         ; Try again if ah != 0

        mov ax, 0
        mov es, ax
        mov bx, 0x1000          ; We load our code at offset: 0:1000h

        mov ah, 02h             ; READ SECTOR-command

mov al, 04h ; Number of sectors to read = 3

Code: Select all

        mov ch, 0               ; Cylinder = 0
        mov cl, 02h             ; Sector = 2
        mov dh, 0               ; Head = 0
        int 13h                 ; Call interrupt 13h
        or ah, ah               ; Check for error code
        jnz reset_drive         ; Try again if ah != 0

[edit]OK, that worked, so how many would you recommend I read in? My goal is to eventually read one file from floppy? Is it smart to read in the whole disk?[/edit]

Posted: **Sun Feb 03, 2008 1:49 pm**

*string++; -> *(string++);

I had a problem like that, and the above fixed it.

-JL

Posted: **Mon Feb 04, 2008 2:42 am**

Hi,

I don't know why you need to dereference 'string' to increment the pointer value anyway...

Cheers,
Adam

OSDev.org

PIC Problem [SOLVED]

PIC Problem [SOLVED]