A20 Line: Difference between revisions
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===Testing A20 line from Protected Mode=== |
===Testing A20 line from Protected Mode=== |
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When in Protected mode it's easier to test A20 because you can access |
When in Protected mode it's easier to test A20 because you can access A20's set memory addresses using any odd megabyte address. |
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<source lang="asm"> |
<source lang="asm"> |
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[bits 32] |
[bits 32] |
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; check |
; check A20 line |
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; returns to caller if |
; returns to caller if A20 gate is cleared. |
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; continues to a20_on if a20 line is set. |
; continues to a20_on if a20 line is set. |
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; written by Elad Ashkcenazi |
; written by Elad Ashkcenazi |
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is_A20_on?: |
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pushad |
pushad |
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cmpsd |
cmpsd |
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popad |
popad |
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jne |
jne A20_on |
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ret |
ret |
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A20_on: |
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a20_on: |
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</source> |
</source> |
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