2 * U-boot - x86 Startup Code
4 * (C) Copyright 2008-2011
5 * Graeme Russ, <graeme.russ@gmail.com>
7 * (C) Copyright 2002,2003
8 * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
10 * See file CREDITS for list of people who contributed to this
13 * This program is free software; you can redistribute it and/or
14 * modify it under the terms of the GNU General Public License as
15 * published by the Free Software Foundation; either version 2 of
16 * the License, or (at your option) any later version.
18 * This program is distributed in the hope that it will be useful,
19 * but WITHOUT ANY WARRANTY; without even the implied warranty of
20 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
21 * GNU General Public License for more details.
23 * You should have received a copy of the GNU General Public License
24 * along with this program; if not, write to the Free Software
25 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
29 #include <asm/global_data.h>
30 #include <asm/processor-flags.h>
32 #define BOOT_SEG 0xffff0000 /* linear segment of boot code */
33 #define a32 .byte 0x67;
34 #define o32 .byte 0x66;
36 .section .start16, "ax"
40 /* Set the Cold Boot / Hard Reset flag */
41 movl $GD_FLG_COLD_BOOT, %ebx
44 * First we let the BSP do some early initialization
45 * this code have to map the flash to its final position
48 .globl board_init16_ret
51 /* Turn of cache (this might require a 486-class CPU) */
53 orl $(X86_CR0_NW | X86_CR0_CD), %eax
57 /* load the temporary Global Descriptor Table */
61 /* Now, we enter protected mode */
66 /* Flush the prefetch queue */
69 /* Finally jump to the 32bit initialization code */
70 movw $code32start, %ax
74 /* 48-bit far pointer */
76 .long _start /* offset */
77 .word 0x10 /* segment */
84 * The following Global Descriptor Table is just enough to get us into
85 * 'Flat Protected Mode' - It will be discarded as soon as the final
86 * GDT is setup in a safe location in RAM
89 .word 0x20 /* limit (32 bytes = 4 GDT entries) */
90 .long BOOT_SEG + gdt /* base */
92 /* Some CPUs are picky about GDT alignment... */
102 * 0x18 32bit data/stack
104 /* The NULL Desciptor - Mandatory */
105 .word 0x0000 /* limit_low */
106 .word 0x0000 /* base_low */
107 .byte 0x00 /* base_middle */
108 .byte 0x00 /* access */
109 .byte 0x00 /* flags + limit_high */
110 .byte 0x00 /* base_high */
112 /* Unused Desciptor - (matches Linux) */
113 .word 0x0000 /* limit_low */
114 .word 0x0000 /* base_low */
115 .byte 0x00 /* base_middle */
116 .byte 0x00 /* access */
117 .byte 0x00 /* flags + limit_high */
118 .byte 0x00 /* base_high */
121 * The Code Segment Descriptor:
122 * - Base = 0x00000000
124 * - Access = Present, Ring 0, Exec (Code), Readable
125 * - Flags = 4kB Granularity, 32-bit
127 .word 0xffff /* limit_low */
128 .word 0x0000 /* base_low */
129 .byte 0x00 /* base_middle */
130 .byte 0x9b /* access */
131 .byte 0xcf /* flags + limit_high */
132 .byte 0x00 /* base_high */
135 * The Data Segment Descriptor:
136 * - Base = 0x00000000
138 * - Access = Present, Ring 0, Non-Exec (Data), Writable
139 * - Flags = 4kB Granularity, 32-bit
141 .word 0xffff /* limit_low */
142 .word 0x0000 /* base_low */
143 .byte 0x00 /* base_middle */
144 .byte 0x93 /* access */
145 .byte 0xcf /* flags + limit_high */
146 .byte 0x00 /* base_high */