/**************************************************************************************
 Copyright (c) 2002 The UbixOS Project
 All rights reserved.

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 $Id: gdt.h,v 1.2 2002/09/29 23:55:15 reddawg Exp $

**************************************************************************************/

#ifndef _GDT_H
#define _GDT_H

// Descriptor Definitions 
#define dCall 0x0C00 // 386 Call Gate                
#define dCode 0x1800 // Code Segment                 
#define dData 0x1000 // Data Segment                 
#define dInt  0x0E00 // 386 Interrupt Gate           
#define dLdt  0x200  // Local Descriptor Table (LDT) 
#define dTask 0x500  // Task gate                    
#define dTrap 0x0F00 // 386 Trap Gate                
#define dTss  0x900  // Task State Segment (TSS)     

// Descriptor Options
#define dDpl3     0x6000 // DPL3 or mask for DPL             
#define dDpl2     0x4000 // DPL2 or mask for DPL             
#define dDpl1     0x2000 // DPL1 or mask for DPL             
#define dPresent  0x8000 // Present                          
#define dNpresent 0x8000 // Not Present                      
#define dAcc      0x100  // Accessed (Data or Code)          
#define dWrite    0x200  // Writable (Data segments only)    
#define dRead     0x200  // Readable (Code segments only)    
#define dBusy     0xB00  // Busy (TSS only)    was 200       
#define dEexdown  0x400  // Expand down (Data segments only) 
#define dConform  0x400  // Conforming (Code segments only)  
#define dBig      0x40   // Default to 32 bit mode           
#define dBiglim   0x80   // Limit is in 4K units             

// GDT Descriptor
struct gdtDescriptor {
  unsigned short limitLow;      // Limit 0..15 
  unsigned short baseLow;       // Base  0..15 
  unsigned char  baseMed;       // Base  16..23
  unsigned char  access;        // Access Byte 
  unsigned int   limitHigh:4;   // Limit 16..19
  unsigned int   granularity:4; // Granularity
  unsigned char  baseHigh;      // Base 24..31
  } __attribute__ ((packed));

struct gdtGate {
  unsigned short offsetLow;  // Offset 0..15
  unsigned short selector;   // Selector      
  unsigned short access;     // Access Flags  
  unsigned short offsetHigh; // Offset 16..31
  } __attribute__ ((packed));

union descriptorTableunion {
  struct gdtDescriptor descriptor; // Normal descriptor
  struct gdtGate gate;             // Gate descriptor  
  unsigned long dummy;             // Any other info 
  };

#define descriptorTable(name,length) union descriptorTableunion name[length] =
#define standardDescriptor(base, limit, control) {descriptor: {(limit & 0xffff), (base & 0xffff), ((base >> 16) & 0xff), \
                                               ((control+dPresent) >> 8), (limit >> 16), \
                                               ((control & 0xff) >> 4), (base >> 24)}}
#define gateDescriptor(offset, selector, control) {gate: {(offset & 0xffff), selector, \
                                                     (control+dPresent), (offset >> 16) }}

#endif