1/* 2 * U-boot - x86 Startup Code 3 * 4 * (C) Copyright 2008-2011 5 * Graeme Russ, <graeme.russ@gmail.com> 6 * 7 * (C) Copyright 2002,2003 8 * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se> 9 * 10 * See file CREDITS for list of people who contributed to this 11 * project. 12 * 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. 17 * 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. 22 * 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, 26 * MA 02111-1307 USA 27 */ 28 29#include <asm/global_data.h> 30#include <asm/processor-flags.h> 31 32#define BOOT_SEG 0xffff0000 /* linear segment of boot code */ 33#define a32 .byte 0x67; 34#define o32 .byte 0x66; 35 36.section .start16, "ax" 37.code16 38.globl start16 39start16: 40 /* 41 * First we let the BSP do some early initialization 42 * this code have to map the flash to its final position 43 */ 44 jmp board_init16 45.globl board_init16_ret 46board_init16_ret: 47 48 /* Turn of cache (this might require a 486-class CPU) */ 49 movl %cr0, %eax 50 orl $(X86_CR0_NW | X86_CR0_CD), %eax 51 movl %eax, %cr0 52 wbinvd 53 54 /* load the temporary Global Descriptor Table */ 55o32 cs lidt idt_ptr 56o32 cs lgdt gdt_ptr 57 58 /* Now, we enter protected mode */ 59 movl %cr0, %eax 60 orl $X86_CR0_PE, %eax 61 movl %eax, %cr0 62 63 /* Flush the prefetch queue */ 64 jmp ff 65ff: 66 /* Finally jump to the 32bit initialization code */ 67 movw $code32start, %ax 68 movw %ax, %bp 69o32 cs ljmp *(%bp) 70 71 /* 48-bit far pointer */ 72code32start: 73 .long _start /* offset */ 74 .word 0x10 /* segment */ 75 76idt_ptr: 77 .word 0 /* limit */ 78 .long 0 /* base */ 79 80/* 81 * The following Global Descriptor Table is just enough to get us into 82 * 'Flat Protected Mode' - It will be discarded as soon as the final 83 * GDT is setup in a safe location in RAM 84 */ 85gdt_ptr: 86 .word 0x20 /* limit (32 bytes = 4 GDT entries) */ 87 .long BOOT_SEG + gdt /* base */ 88 89 /* The GDT table ... 90 * 91 * Selector Type 92 * 0x00 NULL 93 * 0x08 Unused 94 * 0x10 32bit code 95 * 0x18 32bit data/stack 96 */ 97 98gdt: 99 .word 0, 0, 0, 0 /* NULL */ 100 .word 0, 0, 0, 0 /* unused */ 101 102 .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ 103 .word 0 /* base address = 0 */ 104 .word 0x9B00 /* code read/exec */ 105 .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ 106 107 .word 0xFFFF /* 4Gb - (0x100000*0x1000 = 4Gb) */ 108 .word 0x0 /* base address = 0 */ 109 .word 0x9300 /* data read/write */ 110 .word 0x00CF /* granularity = 4096, 386 (+5th nibble of limit) */ 111