diff options
| -rw-r--r-- | mubios/arch/mode_switch.S | 108 | ||||
| -rw-r--r-- | mubios/arch/reset.S | 4 |
2 files changed, 112 insertions, 0 deletions
diff --git a/mubios/arch/mode_switch.S b/mubios/arch/mode_switch.S new file mode 100644 index 0000000..17fbe72 --- /dev/null +++ b/mubios/arch/mode_switch.S @@ -0,0 +1,108 @@ +# RCC-Project +# +# Copyright (C) 2026 Richard Qin +# +# This file is part of RCC-Project. +# +# RCC-Project 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 3 of the License, or (at your option) any +# later version. +# +# RCC-Project 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 +# RCC-Project; see the file COPYING. If not see +# <http://www.gnu.org/licenses/>. + + .intel_syntax noprefix + .code16 + + .section .text16, "ax" + + .global enter_protected_mode + .type enter_protected_mode, @function + +enter_protected_mode: + cli + + # Enable A20 through the fast A20 gate. + + in al, 0x92 + or al, 0x02 + and al, 0xFE + out 0x92, al + + # Make data references address the ROM code segment. + + push cs + pop ds + + call 1f +1: + pop bx + add bx, gdt_descriptor - 1b + lgdt [bx] + + # Enable protected mode + mov eax, cr0 + or eax, 0x00000001 + mov cr0, eax + + # Reload CS with the 32-bit code selector. + .byte 0x66 + .byte 0xEA + .long protected_mode_entry + .word 0x0008 + + .align 8 + +gdt_start: + .quad 0x0000000000000000 + +gdt_code: + .word 0xFFFF + .word 0x0000 + .byte 0x00 + .byte 0x9A + .byte 0xCF + .byte 0x00 + +gdt_data: + .word 0xFFFF + .word 0x0000 + .byte 0x00 + .byte 0x92 + .byte 0xCF + .byte 0x00 + +gdt_end: + +gdt_descriptor: + .word gdt_end - gdt_start - 1 + .long gdt_start + + .code32 + + .section .text32, "ax" + + .global protected_mode_entry + .type protected_mode_entry, @function + +protected_mode_entry: + mov ax, 0x0010 + mov ds, ax + mov es, ax + mov ss, ax + mov fs, ax + mov gs, ax + + mov esp, 0x00008000 + +protected_mode_halt: + hlt + jmp protected_mode_halt + + diff --git a/mubios/arch/reset.S b/mubios/arch/reset.S index b3dbde2..aedf3d1 100644 --- a/mubios/arch/reset.S +++ b/mubios/arch/reset.S @@ -19,6 +19,8 @@ .intel_syntax noprefix .code16 + + .extern enter_protected_mode .section .text16, "ax" @@ -35,6 +37,8 @@ reset_entry: mov ss, ax mov sp, 0x8000 + call enter_protected_mode + reset_halt: hlt jmp reset_halt |