Detecting Memory (x86): Difference between revisions
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BIOS bug |
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====BIOS Function: INT 0x15, AX = 0xDA88==== |
====BIOS Function: INT 0x15, AX = 0xDA88==== |
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This function returns the number of contiguous KiB of usable RAM starting at 0x00100000 in |
This function returns the number of contiguous KiB of usable RAM starting at 0x00100000 in CL:BX in KiB. This is very similar to "INT 0x15, AX=0x8A" - if this function says there's 14 MiB of RAM at 0x00100000 then you can't assume there isn't more RAM at 0x01000000, so you'd probe for any extra memory starting at 0x01000000. |
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If this function isn't supported it'll return "carry = set". |
If this function isn't supported it'll return "carry = set". |
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Note: This function may limit itself to reporting 15M (for legacy reasons) even if BIOS detects more |
Note: This function may limit itself to reporting 15M (for legacy reasons) even if BIOS detects more |
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memory than that. It may also report up to 64M. It only reports contiguous (usable) RAM. |
memory than that. It may also report up to 64M. It only reports contiguous (usable) RAM. In some BIOSes, it may not clear the CF flag on success. |
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Usage: |
Usage: |
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<source lang="asm"> |
<source lang="asm"> |
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CLC ; CF bug workaround |
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MOV AH, 0x88 |
MOV AH, 0x88 |
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INT 0x15 ; request upper memory size |
INT 0x15 ; request upper memory size |
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TEST AX, AX ; size = 0 is an error |
TEST AX, AX ; size = 0 is an error |
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JE SHORT .ERR |
JE SHORT .ERR |
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CMP AH, 0x86 ; unsupported function |
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JE SHORT .ERR |
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CMP AH, 0x80 ; invalid command |
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JE SHORT .ERR |
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</source> |
</source> |
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