Enable A20 gate

[nameless-os.git] / boot / x86 / boot.s

diff --git a/boot/x86/boot.s b/boot/x86/boot.s
index be6c6531d0a581d9c7b49fa91bbd977e6d52f183..572ef74453e99d3efb870ac590d636ed038d7dfa 100644 (file)
--- a/boot/x86/boot.s
+++ b/boot/x86/boot.s
@@ -27,27 +27,34 @@ KERNEL_OFFSET equ 1000h ; where we will load our kernel
        jc read_error ; halt if read fails
        cmp al, 10 ; make sure we actually read 10 sectors
        jl read_error ; halt if we didn't
-       jmp switch_to_pm ; if all is good, begin the switch to 32-bit protected mode
+
+       call check_a20
+       cmp ax, 1
+       jne a20_is_off
+
+a20_is_on
+       jmp switch_to_pm
+a20_is_off
+       call enable_a20
+       jmp switch_to_pm
 
 reset_error
        mov bx, 0B800h
        mov es, bx
        mov byte [es:di], '1'
-       jmp halt
+       jmp $
 
 read_error
        mov bx, 0B800h
        mov es, bx
        mov byte [es:di], '2'
-       jmp halt
-
-halt
        jmp $
 
 %include "a20.s"
+%include "print.s"
 %include "protected.s"
 
-BOOT_DRIVE db 0 ; reserve a spot in RAM for our boot drive variable
+BOOT_DRIVE resb 1
 
        times 510-($-$$) db 0
        dw 0AA55h ; MBR signature