diff options
Diffstat (limited to 'xxx/boot2/memmap.asm')
| -rw-r--r-- | xxx/boot2/memmap.asm | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/xxx/boot2/memmap.asm b/xxx/boot2/memmap.asm new file mode 100644 index 0000000..d101557 --- /dev/null +++ b/xxx/boot2/memmap.asm @@ -0,0 +1,57 @@ +;--------------------------------------------- +; Get memory map from bios +; /in es:di->destination buffer for entries +; /ret bp=entry count +;--------------------------------------------- + +; stolen from: http://www.brokenthorn.com/Resources/OSDev17.html +struc MemoryMapEntry + .baseAddress resq 1 ; base address of address range + .length resq 1 ; length of address range in bytes + .type resd 1 ; type of address range + .acpi_null resd 1 ; reserved +endstruc + +[bits 16] + +BiosGetMemoryMap: + pushad + xor ebx, ebx + xor bp, bp ; number of entries stored here + mov edx, 'PAMS' ; 'SMAP' + mov eax, 0xe820 + mov ecx, 24 ; memory map entry struct is 24 bytes + int 0x15 ; get first entry + jc .error + cmp eax, 'PAMS' ; bios returns SMAP in eax + jne .error + test ebx, ebx ; if ebx=0 then list is one entry long; bail out + je .error + jmp .start +.next_entry: + mov edx, 'PAMS' ; some bios's trash this register + mov ecx, 24 ; entry is 24 bytes + mov eax, 0xe820 + int 0x15 ; get next entry +.start: + jcxz .skip_entry ; if actual returned bytes is 0, skip entry +.notext: + mov ecx, [es:di + MemoryMapEntry.length] ; get length (low dword) + test ecx, ecx ; if length is 0 skip it + jne short .good_entry + mov ecx, [es:di + MemoryMapEntry.length + 4]; get length (upper dword) + jecxz .skip_entry ; if length is 0 skip it +.good_entry: + inc bp ; increment entry count + add di, 24 ; point di to next entry in buffer +.skip_entry: + cmp ebx, 0 ; if ebx return is 0, list is done + jne .next_entry ; get next entry + jmp .done +.error: + stc +.done: + + mov [MEMMAP_SIZE_OFFSET],bp + popad + ret |