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 * SPDX-License-Identifier: GPL-2.0+ 11 */ 12 13#include <asm/global_data.h> 14#include <asm/processor-flags.h> 15 16#define BOOT_SEG 0xffff0000 /* linear segment of boot code */ 17#define a32 .byte 0x67; 18#define o32 .byte 0x66; 19 20.section .start16, "ax" 21.code16 22.globl start16 23start16: 24 /* Save BIST */ 25 movl %eax, %ecx 26 27 /* Set the Cold Boot / Hard Reset flag */ 28 movl $GD_FLG_COLD_BOOT, %ebx 29 30 xorl %eax, %eax 31 movl %eax, %cr3 /* Invalidate TLB */ 32 33 /* Turn off cache (this might require a 486-class CPU) */ 34 movl %cr0, %eax 35 orl $(X86_CR0_NW | X86_CR0_CD), %eax 36 movl %eax, %cr0 37 wbinvd 38 39 /* load the temporary Global Descriptor Table */ 40o32 cs lidt idt_ptr 41o32 cs lgdt gdt_ptr 42 43 /* Now, we enter protected mode */ 44 movl %cr0, %eax 45 orl $X86_CR0_PE, %eax 46 movl %eax, %cr0 47 48 /* Flush the prefetch queue */ 49 jmp ff 50ff: 51 52 /* Finally restore BIST and jump to the 32-bit initialization code */ 53 movw $code32start, %ax 54 movw %ax, %bp 55 movl %ecx, %eax 56o32 cs ljmp *(%bp) 57 58 /* 48-bit far pointer */ 59code32start: 60 .long _start /* offset */ 61 .word 0x10 /* segment */ 62 63idt_ptr: 64 .word 0 /* limit */ 65 .long 0 /* base */ 66 67 /* 68 * The following Global Descriptor Table is just enough to get us into 69 * 'Flat Protected Mode' - It will be discarded as soon as the final 70 * GDT is setup in a safe location in RAM 71 */ 72gdt_ptr: 73 .word 0x1f /* limit (31 bytes = 4 GDT entries - 1) */ 74 .long BOOT_SEG + gdt_rom /* base */ 75 76 /* Some CPUs are picky about GDT alignment... */ 77 .align 16 78.globl gdt_rom 79gdt_rom: 80 /* 81 * The GDT table ... 82 * 83 * Selector Type 84 * 0x00 NULL 85 * 0x08 Unused 86 * 0x10 32bit code 87 * 0x18 32bit data/stack 88 */ 89 /* The NULL Desciptor - Mandatory */ 90 .word 0x0000 /* limit_low */ 91 .word 0x0000 /* base_low */ 92 .byte 0x00 /* base_middle */ 93 .byte 0x00 /* access */ 94 .byte 0x00 /* flags + limit_high */ 95 .byte 0x00 /* base_high */ 96 97 /* Unused Desciptor - (matches Linux) */ 98 .word 0x0000 /* limit_low */ 99 .word 0x0000 /* base_low */ 100 .byte 0x00 /* base_middle */ 101 .byte 0x00 /* access */ 102 .byte 0x00 /* flags + limit_high */ 103 .byte 0x00 /* base_high */ 104 105 /* 106 * The Code Segment Descriptor: 107 * - Base = 0x00000000 108 * - Size = 4GB 109 * - Access = Present, Ring 0, Exec (Code), Readable 110 * - Flags = 4kB Granularity, 32-bit 111 */ 112 .word 0xffff /* limit_low */ 113 .word 0x0000 /* base_low */ 114 .byte 0x00 /* base_middle */ 115 .byte 0x9b /* access */ 116 .byte 0xcf /* flags + limit_high */ 117 .byte 0x00 /* base_high */ 118 119 /* 120 * The Data Segment Descriptor: 121 * - Base = 0x00000000 122 * - Size = 4GB 123 * - Access = Present, Ring 0, Non-Exec (Data), Writable 124 * - Flags = 4kB Granularity, 32-bit 125 */ 126 .word 0xffff /* limit_low */ 127 .word 0x0000 /* base_low */ 128 .byte 0x00 /* base_middle */ 129 .byte 0x93 /* access */ 130 .byte 0xcf /* flags + limit_high */ 131 .byte 0x00 /* base_high */ 132