diff options
Diffstat (limited to 'roms/u-boot/arch/x86/cpu/start16.S')
| -rw-r--r-- | roms/u-boot/arch/x86/cpu/start16.S | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/roms/u-boot/arch/x86/cpu/start16.S b/roms/u-boot/arch/x86/cpu/start16.S new file mode 100644 index 000000000..865a49731 --- /dev/null +++ b/roms/u-boot/arch/x86/cpu/start16.S @@ -0,0 +1,122 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * U-Boot - x86 Startup Code + * + * (C) Copyright 2008-2011 + * Graeme Russ, <graeme.russ@gmail.com> + * + * (C) Copyright 2002,2003 + * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se> + */ + +#include <asm/processor-flags.h> + +#define BOOT_SEG 0xffff0000 /* linear segment of boot code */ + +.section .start16, "ax" +.code16 +.globl start16 +start16: + /* Save BIST */ + movl %eax, %ecx + + xorl %eax, %eax + movl %eax, %cr3 /* Invalidate TLB */ + + /* Turn off cache (this might require a 486-class CPU) */ + movl %cr0, %eax + orl $(X86_CR0_NW | X86_CR0_CD), %eax + movl %eax, %cr0 + wbinvd + + /* load the temporary Global Descriptor Table */ +data32 cs lidt idt_ptr +data32 cs lgdt gdt_ptr + + /* Now, we enter protected mode */ + movl %cr0, %eax + orl $X86_CR0_PE, %eax + movl %eax, %cr0 + + /* Flush the prefetch queue */ + jmp ff +ff: + + /* Finally restore BIST and jump to the 32-bit initialization code */ + movl %ecx, %eax +data32 cs ljmp *code32start + + /* 48-bit far pointer */ +code32start: + .long _start /* offset */ + .word 0x10 /* segment */ + +idt_ptr: + .word 0 /* limit */ + .long 0 /* base */ + + /* + * The following Global Descriptor Table is just enough to get us into + * 'Flat Protected Mode' - It will be discarded as soon as the final + * GDT is setup in a safe location in RAM + */ +gdt_ptr: + .word 0x1f /* limit (31 bytes = 4 GDT entries - 1) */ + .long BOOT_SEG + gdt_rom /* base */ + + /* Some CPUs are picky about GDT alignment... */ + .align 16 +.globl gdt_rom +gdt_rom: + /* + * The GDT table ... + * + * Selector Type + * 0x00 NULL + * 0x08 Unused + * 0x10 32bit code + * 0x18 32bit data/stack + */ + /* The NULL Desciptor - Mandatory */ + .word 0x0000 /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x00 /* access */ + .byte 0x00 /* flags + limit_high */ + .byte 0x00 /* base_high */ + + /* Unused Desciptor - (matches Linux) */ + .word 0x0000 /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x00 /* access */ + .byte 0x00 /* flags + limit_high */ + .byte 0x00 /* base_high */ + + /* + * The Code Segment Descriptor: + * - Base = 0x00000000 + * - Size = 4GB + * - Access = Present, Ring 0, Exec (Code), Readable + * - Flags = 4kB Granularity, 32-bit + */ + .word 0xffff /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x9b /* access */ + .byte 0xcf /* flags + limit_high */ + .byte 0x00 /* base_high */ + + /* + * The Data Segment Descriptor: + * - Base = 0x00000000 + * - Size = 4GB + * - Access = Present, Ring 0, Non-Exec (Data), Writable + * - Flags = 4kB Granularity, 32-bit + */ + .word 0xffff /* limit_low */ + .word 0x0000 /* base_low */ + .byte 0x00 /* base_middle */ + .byte 0x93 /* access */ + .byte 0xcf /* flags + limit_high */ + .byte 0x00 /* base_high */ |