Add realmode warm booter

diff --git a/grubload/realmode.asm b/grubload/realmode.asm
new file mode 100644 (file)
index 0000000..b504b00
--- /dev/null
+++ b/grubload/realmode.asm
@@ -0,0 +1,106 @@
+       [bits 32]       ; Starts in 32 bit mode, then will drop back later.
+       org 0x4000
+entry:
+       cli
+       ; clean up 32 bit regs
+       mov eax, 0x0
+       mov ebx, 0x0
+       mov ecx, 0x0
+       mov edx, 0x0
+       mov esi, 0x0
+       mov edi, 0x0
+       mov ebp, 0x0
+       mov esp, 0x0
+       
+       lgdt [gdtp]
+       
+       mov ax, 0x10
+       mov ds, ax
+       mov es, ax
+       mov fs, ax
+       mov gs, ax
+       mov ss, ax
+       
+       jmp 0x8:nextp   ; Clear CS bits now too
+
+nextp:
+       
+       mov eax, cr0
+       xor eax, 0x1    ; Clear PE
+       mov cr0, eax
+       
+       jmp 0x0:nowreal ; and jmp away
+
+
+       [bits 16]
+nowreal:
+       mov long eax, 0x0000
+       mov ds, ax
+       mov es, ax
+       mov fs, ax
+       mov gs, ax
+       mov ss, ax
+       
+       mov sp, 0xFFFF  ; set up the stack
+
+       mov al, 0xAB
+       out 0x80, al
+
+       cli
+       lidt [idtp]
+
+       mov si, RETMSG
+       call disp
+
+       int 0x19                ; warm boot without clearing RAM.
+       call handload_drive     ; hopefully shouldn't happen
+       ; ok, we give up
+       cli
+halt:  hlt
+       jmp halt
+
+disp:
+       lodsb
+       or al, al
+       jz .done
+       mov ah, 0x0E
+       mov bx, 0x0007
+       int 0x10
+       jmp disp
+.done:
+       ret
+
+; handload_drive should be unnecessary; int 19 should take care of it for
+; us...
+handload_drive:
+       mov ax, 0x07C0
+       mov es, ax
+       mov ax, 0x0201  ; read one sector
+       mov bx, 0x0000  ; to the normal location
+       mov cx, 0x0001  ; disk sector 1
+       mov dx, 0x0080  ; drive 0
+       int 0x13
+       jc readerr
+       
+       mov si, READSUCC
+       call disp
+       
+       jmp 0x7C0:0x0   ; and return control to grub!
+readerr:
+       mov si, READFAIL
+       call disp
+       ret
+
+RETMSG db "SMM installer finished, booting your system of choice.",10,13,0
+READSUCC db "Read successful; rebooting into boot sector.",10,13,0
+READFAIL db "Boot disk read failure; system halted.",10,13,0
+
+
+idtp   db 0xFF, 0x03, 0x00, 0x00, 0x00, 0x00
+
+gdtp   dw 0x1F
+       dd gdt
+
+gdt    dd 0, 0
+       dd 0x0000FFFF, 0x00009e00       ; CS
+       dd 0x0000FFFF, 0x00009300       ; DS