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Here a part of the code of my kernel
it handles the multitasking ...
if i switch the task with switch_task(0x28);
the pc reboots or he?s halting
but he should print out many Y on the screen


****************************************
#define ACCESSED   0x01
#define DATASEG_NOTREADABLE  0x00
#define DATASEG    0x02
#define DATASEG_RESERVED  0x04
#define DATASEG_EXPANDABLE    0x06
#define CODESEG_NOTREADABLE  0x08
#define CODESEG    0x0A
#define CODESEG_CONFORM_NR  0x0C
#define CODESEG_CONFORM   0x0E
#define SEGMENT    0x10
#define SYSTEM    0x00
#define DPL0    0x00
#define DPL1    0x20
#define DPL2    0x40
#define DPL3    0x60
#define PRESENT    0x80


#define TSS_80286   0x01
#define LDT    0x02
#define TSS_80286_ACTIVE  0x03
#define CALLGATE_80286   0x04
#define TASKGATE   0x05
#define INTGATE_80286   0x06
#define TRAPGATE_80286   0x07
#define TSS_80386   0x09
#define TSS_80386_ACTIVE  0x0B
#define CALLGATE_80386   0x0C
#define INTGATE_80386   0x0E
#define TRAPGATE_80386   0x0F


#define GRAN    0x40;
#define _80386    0x30;
#define AVL    0x10;



*********************************
typedef struct
{
unsigned short seg_0_15;
unsigned short addr_0_15;
unsigned char addr_16_23;
unsigned char type;
unsigned char seg_16_19;
unsigned char addr_24_31;
}__attribute__((packed)) DESK;

struct task_gate
{
unsigned long reserviert1;
unsigned long selektor;
unsigned char reserviert2;
unsigned char type;
unsigned long reserviert3;
}__attribute__((packed));


typedef struct
{
  unsigned short backlink, __blh;
  unsigned long esp0;
  unsigned short ss0, __ss0h;
  unsigned long esp1;
  unsigned short ss1, __ss1h;
  unsigned long esp2;
  unsigned short ss2, __ss2h;
  unsigned long cr3, eip, eflags;
  unsigned long eax,ecx,edx,ebx,esp,ebp,esi,edi;
  unsigned short es, __esh;
  unsigned short cs, __csh;
  unsigned short ss, __ssh;
  unsigned short ds, __dsh;
  unsigned short fs, __fsh;
  unsigned short gs, __gsh;
  unsigned short ldt, __ldth;
  unsigned short trace, iomapbase;
}__attribute__((packed)) TSS_STRUCT;

void init_task(unsigned char num,void *taskaddresse)
{
tasktabelle[num].esp=0xFFFF;
tasktabelle[num].es=0x8;
tasktabelle[num].cs=0x10;
tasktabelle[num].ss=0x18;
tasktabelle[num].ds=0x8;
tasktabelle[num].fs=0;
tasktabelle[num].gs=0;
tasktabelle[num].eip=(unsigned long)taskaddresse;
tasktabelle[num].eflags=0x0002;
tasktabelle[num].iomapbase=sizeof(TSS_STRUCT);
}

void ltr(unsigned short selector)
{
  asm ("ltr %0": :"r" (selector));
}

void switch_task(unsigned int selector)
{
  unsigned int sel[2];
  sel[1] = selector;

  asm ("ljmp %0": :"m" (*sel));
}


void desk(unsigned char num,unsigned long segsize,void *addr,unsigned char
type,unsigned char gran)
{
unsigned char a=0;
a=(unsigned long)addr;

gdt[num].seg_0_15=segsize & 0xffff;
gdt[num].seg_16_19=(segsize >> 16) & 0xFF;
gdt[num].type=type;
gdt[num].seg_16_19+=gran;

gdt[num].addr_0_15=a & 0xffff;
gdt[num].addr_16_23=(a >> 16) & 0xFF;
gdt[num].addr_24_31=(a >> 24) & 0xFF;
}
TSS_STRUCT tasktabelle[10];
DESK gdt[256];
**************task o**********************
void o()
{
go:
putchar('Y');
goto go;
}
****************************************
void main()
{
desk(0,0,0,0,0);
desk(1,0xFFFFF,0,DATASEG | SEGMENT | DPL0 | PRESENT,0xbf);
desk(2,0xFFFFF,0,CODESEG | SEGMENT | DPL0 | PRESENT,0xbf);
desk(3,0xFFFF,0, DATASEG | SEGMENT | DPL0 | PRESENT,0);

//somecode....
//....loading the gdt idt init the pit the pic and and and...


init_task(0,0);
init_task(1,o);

desk(4,sizeof(TSS_STRUCT),&tasktabelle[0],TSS_80386 | PRESENT,0);
desk(5,sizeof(TSS_STRUCT),&tasktabelle[1],TSS_80386 | PRESENT,0);
ltr(0x20);
switch_task(0x28);
//.....
//....
}
****************************************
please if someone could help me ... help me

[email protected]
or
[email protected]
or over the board

the selector for the first task(kernel) is 0x20
the second for o(); is 0x28

problem solved in function desk false cast