protected mode problem

[tyler]

For some reason, as soon as I set the first bit of cr0 to enter protected mode, my computer restarts.  Gereral protection error?  Any help would be greatly appreciated.

Thanks,

Tyler

[tyler]

lgdt [gSize] ; load GDTR with base and limit address

mov eax, cr0
or eax, 1 ; set first bit to 1 (pmode)
mov cr0, eax ; move value into cr0

ret ; return for now

gdt: ; create gdt (this label marks start of gdt)

null_descriptor: ; first descriptor in gdt needs to be null

dw 0x0
dw 0x0
dw 0x0
dw 0x0

code_descriptor: ; code descriptor

dw 0xffff ; segment base address
dw 0x0000 ; segment limit
db 0x0 ; base
db 10011010b
db 11001111b
db 0x0

data_descriptor ; data descriptor

dw 0xffff ; segment base address
dw 0x0000 ; segment limit
db 0x0 ; base
db 10010010b
db 11001111b
db 0x0

gdt_end:

gSize: ; these values loaded into gdtr with lgdtr

dw (3*8)-1 ; 16 bit limit address
dd gdt ; 32 bit base address

[ASHLEY4]

Do you do this in your code "cli" (clear interrutpt flag) before go into pmode ?.

ASHLEY4.

[tyler]

Thanks for your prompt reply..

I do clear interrupts before enabling protected mode...

Maybe it has to do with my enabling my 21'st address line incorrectly?

Thanks again.

Tyler