A20 Line: Difference between revisions

</source>

===Testing A20 line from Protected Mode===

When in Protected mode it's easier to test A20 because you can access a20's set memory addresses using any odd megabyte address.

<source lang="asm">

[bits 32]

; written by Elad Ashkcenazi

is_a20_on?:

pushad

mov edi,0x112345 ;odd megabyte address.

mov esi,0x012345 ;even megabyte address.

mov [esi],esi

mov [edi],edi

cmpsd

popad

jne a20_on

ret

a20_on: