* Patch by Daniel Engström, 13 Nov 2002:
Add support for i386 architecture and AMD SC520 board
* Patch by Pierre Aubert, 12 Nov 2002:
Add support for DOS filesystem and booting from DOS floppy disk
diff --git a/lib_i386/realmode_switch.S b/lib_i386/realmode_switch.S
new file mode 100644
index 0000000..9f212c2
--- /dev/null
+++ b/lib_i386/realmode_switch.S
@@ -0,0 +1,223 @@
+/*
+ * (C) Copyright 2002
+ * Daniel Engström, Omicron Ceti AB, daniel@omicron.se
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+
+/* 32bit -> 16bit -> 32bit mode switch code */
+
+/*
+ * Stack frame at 0xe00
+ * e00 ebx;
+ * e04 ecx;
+ * e08 edx;
+ * e0c esi;
+ * e10 edi;
+ * e14 ebp;
+ * e18 eax;
+ * e1c ds;
+ * e20 es;
+ * e24 fs;
+ * e28 gs;
+ * e2c orig_eax;
+ * e30 eip;
+ * e34 cs;
+ * e38 eflags;
+ * e3c esp;
+ * e40 ss;
+ */
+
+#define a32 .byte 0x67; /* address size prefix 32 */
+#define o32 .byte 0x66; /* operand size prefix 32 */
+
+.section .realmode, "ax"
+.code16
+
+ /* 16bit protected mode code here */
+.globl realmode_enter
+realmode_enter:
+o32 pusha
+o32 pushf
+ cli
+ sidt saved_idt
+ sgdt saved_gdt
+ movl %esp, %eax
+ movl %eax, saved_protected_mode_esp
+
+ movl $0x10, %eax
+ movl %eax, %esp
+ movw $0x28, %ax
+ movw %ax, %ds
+ movw %ax, %es
+ movw %ax, %fs
+ movw %ax, %gs
+
+ lidt realmode_idt_ptr
+ movl %cr0, %eax /* Go back into real mode by */
+ andl $0x7ffffffe, %eax /* clearing PE to 0 */
+ movl %eax, %cr0
+ ljmp $0x0,$do_realmode /* switch to real mode */
+
+do_realmode: /* realmode code from here */
+ movw %cs,%ax
+ movw %ax,%ds
+ movw %ax,%es
+ movw %ax,%fs
+ movw %ax,%gs
+
+ /* create a temporary stack */
+
+ movw $0xc0, %ax
+ movw %ax, %ss
+ movw $0x200, %ax
+ movw %ax, %sp
+
+ popl %ebx
+ popl %ecx
+ popl %edx
+ popl %esi
+ popl %edi
+ popl %ebp
+ popl %eax
+ movl %eax, temp_eax
+ popl %eax
+ movw %ax, %ds
+ popl %eax
+ movw %ax, %es
+ popl %eax
+ movw %ax, %fs
+ popl %eax
+ movw %ax, %gs
+ popl %eax /* orig_eax */
+ popl %eax
+cs movw %ax, temp_ip
+ popl %eax
+cs movw %ax, temp_cs
+o32 popf
+ popl %eax
+ popw %ss
+ movl %eax, %esp
+cs movl temp_eax, %eax
+ wbinvd /* self-modifying code,
+ * better flush the cache */
+
+ .byte 0x9a /* lcall */
+temp_ip:
+ .word 0 /* new ip */
+temp_cs:
+ .word 0 /* new cs */
+realmode_ret:
+ /* save eax, esp and ss */
+cs movl %eax, saved_eax
+ movl %esp, %eax
+cs movl %eax, saved_esp
+ movw %ss, %ax
+cs movw %ax, saved_ss
+
+ /* restore the stack, note that we set sp to 0x244;
+ * pt_regs is 0x44 bytes long and we push the structure
+ * backwards on to the stack, bottom first */
+
+ movw $0xc0, %ax
+ movw %ax, %ss
+ movw $0x244, %ax
+ movw %ax, %sp
+
+ xorl %eax,%eax
+cs movw saved_ss, %ax
+ pushl %eax
+cs movl saved_esp, %eax
+ pushl %eax
+o32 pushf
+ xorl %eax,%eax
+cs movw temp_cs, %ax
+ pushl %eax
+cs movw temp_ip, %ax
+ pushl %eax
+ pushl $0
+ movw %gs, %ax
+ pushl %eax
+ movw %fs, %ax
+ pushl %eax
+ movw %es, %ax
+ pushl %eax
+ movw %ds, %ax
+ pushl %eax
+ movl saved_eax, %eax
+ pushl %eax
+ pushl %ebp
+ pushl %edi
+ pushl %esi
+ pushl %edx
+ pushl %ecx
+ pushl %ebx
+
+o32 cs lidt saved_idt
+o32 cs lgdt saved_gdt /* Set GDTR */
+
+ movl %cr0, %eax /* Go back into protected mode */
+ orl $1,%eax /* reset PE to 1 */
+ movl %eax, %cr0
+ jmp next_line /* flush prefetch queue */
+next_line:
+ movw $return_ptr, %ax
+ movw %ax,%bp
+o32 cs ljmp *(%bp)
+
+.code32
+protected_mode:
+ movl $0x18,%eax /* reload GDT[3] */
+ movw %ax,%fs /* reset FS */
+ movw %ax,%ds /* reset DS */
+ movw %ax,%gs /* reset GS */
+ movw %ax,%es /* reset ES */
+ movw %ax,%ss /* reset SS */
+ movl saved_protected_mode_esp, %eax
+ movl %eax, %esp
+ popf
+ popa
+ ret
+
+temp_eax:
+ .long 0
+
+saved_ss:
+ .word 0
+saved_esp:
+ .long 0
+saved_eax:
+ .long 0
+
+realmode_idt_ptr:
+ .word 0x400
+ .word 0x0, 0x0
+
+saved_gdt:
+ .word 0, 0, 0, 0
+saved_idt:
+ .word 0, 0, 0, 0
+
+saved_protected_mode_esp:
+ .long 0
+
+return_ptr:
+ .long protected_mode
+ .word 0x10