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[nyax.git] / stage2 / mmap.asm

diff --git a/stage2/mmap.asm b/stage2/mmap.asm
new file mode 100644 (file)
index 0000000..15c81f8
--- /dev/null
+++ b/stage2/mmap.asm
@@ -0,0 +1,60 @@
+%define MAPMAGIC 0x534D4150
+
+mmap:
+       mov ebx, .msg
+       call print_str
+
+       xor ebx, ebx    ; counter for interrupt
+       mov di, MEMMAP
+
+.loop:
+       ; issue an INT 0x15, EAX = 0xE820 interrupt
+       mov eax, 0xE820
+       mov ecx, 24
+       mov edx, MAPMAGIC
+       int 0x15
+
+       cmp eax, MAPMAGIC ; detect failure
+       jne .fail
+
+       mov eax, [di+16]
+       cmp eax, 2
+       ja .next
+
+       mov eax, [di+4]
+       cmp eax, 0
+       jne .keep
+
+       mov eax, [di+0]
+       cmp eax, 0x100000
+       jb .next
+
+.keep:
+       add di, 24
+
+.next:
+       cmp ebx, 0
+       jne .loop
+
+       mov ax, di
+       sub ax, MEMMAP
+       xor dx, dx
+       mov bx, 24
+       div bx
+       mov [MEMMAPCNT], ax
+
+       mov eax, MEMMAPCNT
+       call print_dec
+       call newline
+       ;jmp $
+
+       ret
+
+.fail:
+       mov ebx, .fail_msg
+       call print_str
+       jmp $
+
+.msg: db "getting extended memory map", 10, 13, 0
+.fail_msg: db "memory map failure", 10, 13, 0
+