gdt.asm

TestOS - 带简单GUI的DOS扩展OS// 源代码// ASM// 英文

;=========================================================;
; Gdt                                            11/12/03 ;
;---------------------------------------------------------;
; DOS EXTREME OS V0.01                                    ;
; by Craig Bamford.                                       ;
;                                                         ;
; Defines gdt descriptors                                 ;                
;=========================================================;

gdt:	                                   ; Address for the gdt 
        dw 0			           ; limit 15:0    (0h) Null Segment
	dw 0			           ; base 15:0
	db 0			           ; base 23:16
	db 0			           ; type
	db 0			           ; limit 19:16, flags
	db 0			           ; base 31:24

linear_sel_1:	
       dw 0xFFFF		           ; (8h) linear Data segment, read/write, expand down
       dw 0			                   
       db 0
       db 10010010b		                   
       db 11001111b                               
       db 0

sys_code_1:                                ; (10h) Code segment, read/execute, nonconforming
       dw 0FFFFh
       dw 0
       db 0
       db 10011010b
       db 11001111b
       db 0

sys_data_1:                                ; (18h) Data segment, read/write, expand down
       dw 0FFFFh
       dw 0
       db 0
       db 10010010b
       db 11001111b
       db 0

Real_code_1:                               ; (20h) Real mode code segment
       dw 0xFFFF
       dw 0			                         
       db 0
       db 10011010b			                          
       db 0			                          
       db 0

Real_data_1:                               ; (28h) Real mode data segment
       dw 0xFFFF
       dw 0			                          
       db 0
       db 10010010b			                          
       db 0			                          
       db 0

gdt_end:                                   ; Used to calculate the size of the GDT