From: Joshua Wise <joshua@rebirth.joshuawise.com>
Date: Wed, 10 Sep 2008 22:22:48 +0000 (-0400)
Subject: Add realmode warm booter
X-Git-Url: http://git.joshuawise.com/netwatch.git/commitdiff_plain/042eafc7086afa192bd8cc0a19f5726bb6df516b?hp=f16f4f1e99d1b45e7f0ba828616c1afdd1b50721

Add realmode warm booter
---

diff --git a/grubload/realmode.asm b/grubload/realmode.asm
new file mode 100644
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