* 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

1 files changed, 223 insertions, 0 deletions

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