void constructGDT(){
uint8_t acs, atr;
acs = 0; atr = 0;
uint32_t limit = 0;
uint32_t base = 0;
initGDTEntry(&gdt[0], base, limit, acs, atr);
limit = 655359; acs = 154; atr = 64;
initGDTEntry(&gdt[1], base, limit, acs, atr);
acs = 146;
initGDTEntry(&gdt[2], base, limit, acs, atr);
initGDTEntry(&gdt[3], base, limit, acs, atr);
base = 753664; limit = 3999;
initGDTEntry(&gdt[4], base, limit, acs, atr);
}
void gdt_install()
{
/* setup the GDT pointer and limit */
gp.limit=(sizeof(struct gdt_entry)*5)-1;
gp.base= (unsigned int)gdt;
/* NULL descriptor */
initGDTEntry(0,0,0,0,0);
/* Code Segment Descriptor , limit 4GB,granularity 4Kb,
32bit opcode*/
/*gdt_set_gate(num,base,limit,access,gran)*/
initGDTEntry(1,0,640*1024-1,0x9A,0x40);
/* Data Segment */
initGDTEntry(2,0,640*1024-1,0x92,0x40);
/* stack segment*/
initGDTEntry(3,0,640*1024-1,0x92,0x40);
/* video segment */
initGDTEntry(4,0xb8000,0xF9F,0x92,0x40); /* F9F hex value of 80*25*2-1*/
/* Flush old GDT*/
_linker(&gp);
gdt_flush(8,16,24,16,16,32); /* 1x8 for CS
(2x8) for DS
(3x8) for SS
4x8 for es */
}
