;
; Parameters
;   X64 - 64 bit target
;   LEGACY_A20 - use slow A20 Gate
;   CHARACTER_TO_SHOW - character to display
;   FORCE_TEXT_MODE - switch to 80x25 mono mode
;

%ifdef LEGACY_A20
DELAY_PORT:             equ 0xed        ; Port to use for 1uS delay
KBD_CONTROL_PORT:       equ 0x60        ; 8042 control port
KBD_STATUS_PORT:        equ 0x64        ; 8042 status port
WRITE_DATA_PORT_CMD:    equ 0xd1        ; 8042 command to write the data port
ENABLE_A20_CMD:         equ 0xdf        ; 8042 command to enable A20
%else
FAST_ENABLE_A20_PORT:   equ 0x92
FAST_ENABLE_A20_MASK:   equ 2
%endif
BASE_ADR_16:            equ 0x0200
SIZE_TO_STACK_16:       equ 0x0fe0 - BASE_ADR_16
IA32_EFER:              equ 0xC0000080

%assign GDT_DESC_SIZE 8
%macro GDT_DESC 2
        dw 0xFFFF, 0
        db 0, %1, %2, 0
%endmacro

%ifdef X64
  %assign IDT_DESC_SIZE 16
  %macro IDT_DESC 0
        dw 0, SYS_CODE64_SEL
        db 0, 0x8e
        dw 0
        dd 0, 0
  %endmacro
%else
  %assign IDT_DESC_SIZE 8
  %macro IDT_DESC 0
        dw 0, SYS_CODE_SEL
        db 0, 0x8e
        dw 0
  %endmacro
%endif

%ifdef X64
    section .pagezero start=0
    times BASE_ADR_16 db 0

    %ifndef PAGE_TABLE
        %error "PAGE_TABLE is not defined!"
    %endif
%endif

        bits 16

        section .text start=BASE_ADR_16

global _start
_start:
        jmp     .SkipLabel
%ifdef X64
        db      'DUETX64   '    ; Bootloader Label
%else
        db      'DUETIA32  '    ; Bootloader Label
%endif
.SkipLabel:
        mov     ax, cs
        mov     ds, ax
        mov     es, ax
        mov     ss, ax
        mov     sp, MyStack

;
; Retrieve Bios Memory Map
;
        xor     ebx, ebx
        lea     edi, [MemoryMap]
.MemMapLoop:
        mov     eax, 0xe820
        mov     ecx, 20
        mov     edx, 0x534d4150         ; SMAP
        int     0x15
        jc      .MemMapDone
        add     di, 20
        test    ebx, ebx
        jnz     .MemMapLoop
.MemMapDone:
        sub     di, MemoryMap           ; Get the address of the memory map
        mov     [MemoryMapSize], edi    ; Save the size of the memory map

;
; Rebase Self
;
        xor     ebx, ebx
        mov     bx, cs
        shl     ebx, 4
        add     [gdtr + 2], ebx
        add     [idtr + 2], ebx
        add     [.JumpTo32BitProtectedMode], ebx
%ifdef X64
        add     [.JumpToLongMode], ebx
%endif

;
; Enable A20 Gate
;
        mov     ax, 0x2401
        int     0x15
        jnc     .A20GateEnabled

;
; If INT 15 Function 2401 is not supported, then attempt to Enable A20 manually.
;

%ifdef LEGACY_A20
;
; Legacy A20gate
;
        call    Empty8042InputBuffer    ; Empty the Input Buffer on the 8042 controller
        jnz     .Timeout8042            ; Jump if the 8042 timed out
        out     DELAY_PORT, ax          ; Delay 1 uS
        mov     al, WRITE_DATA_PORT_CMD ; 8042 cmd to write output port
        out     KBD_STATUS_PORT, al     ; Send command to the 8042
        call    Empty8042InputBuffer    ; Empty the Input Buffer on the 8042 controller
        jnz     .Timeout8042            ; Jump if the 8042 timed out
        mov     al, ENABLE_A20_CMD      ; gate address bit 20 on
        out     KBD_CONTROL_PORT,al     ; Send command to thre 8042
        call    Empty8042InputBuffer    ; Empty the Input Buffer on the 8042 controller
        mov     cx, 25                  ; Delay 25 uS for the command to complete on the 8042
.Delay25uS:
        out     DELAY_PORT, ax          ; Delay 1 uS
        loop    .Delay25uS
.Timeout8042:

%else
;
; WIKI - fast A20gate
;
        in      al, FAST_ENABLE_A20_PORT
        or      al, FAST_ENABLE_A20_MASK
        out     FAST_ENABLE_A20_PORT, al

%endif

.A20GateEnabled:

%ifdef FORCE_TEXT_MODE
;
; Switch to 80x25 mono text mode (2)
;
        mov     ax, 2
        int     0x10
%endif

%ifdef CHARACTER_TO_SHOW

;
; Display CHARACTER_TO_SHOW
;
        mov     bx, 0x000F
        mov     ax, 0x0E00 | (CHARACTER_TO_SHOW & 255)
        int     0x10

%endif

%ifndef X64
        mov     bx, LINEAR_SEL  ; Flat data descriptor
%endif

;
; DISABLE INTERRUPTS - Entering Protected Mode
;
        cli

;
; load GDT
;
        lgdt [gdtr]

%ifndef X64
;
; load IDT
;
        lidt [idtr]
%endif

;
; Enable Protected Mode (set CR0.PE=1)
;
        mov     eax, cr0
        or      al, 1
        mov     cr0, eax

.JumpTo32BitProtectedMode:      equ $ + 2
%ifndef X64
        jmp     dword LINEAR_CODE_SEL:(BlockSignature + 2)
%else
        jmp     dword LINEAR_CODE_SEL:.In32BitProtectedMode
.In32BitProtectedMode:

        bits 32
;
; Entering Long Mode
;
        mov     ax, LINEAR_SEL
        mov     ds, eax
        mov     es, eax
        mov     ss, eax
; WARNING: esp invalid here

;
; Enable the 64-bit page-translation-table entries by
; setting CR4.PAE=1 (this is _required_ before activating
; long mode). Paging is not enabled until after long mode
; is enabled.
;
        mov     eax, cr4
        or      al, 0x20
        mov     cr4, eax

;
; This is the Trapolean Page Tables that are guarenteed
;  under 4GB.
;
; Address Map:
;    10000 ~    12000 - efildr (loaded)
;    20000 ~    21000 - start64.com
;    21000 ~    22000 - efi64.com
;    22000 ~    90000 - efildr
;    90000 ~    96000 - 4G pagetable (will be reload later)
;
        mov     eax, PAGE_TABLE
        mov     cr3, eax

;
; Enable long mode (set EFER.LME=1).
;
        mov     ecx, IA32_EFER
        rdmsr
        or      ax, 0x100
        wrmsr

;
; Enable Paging to activate long mode (set CR0.PG=1)
;
        mov     eax, cr0
        bts     eax, 31
        mov     cr0, eax

.JumpToLongMode:        equ $ + 1
        jmp     SYS_CODE64_SEL:.InLongMode
.InLongMode:

        bits 64

        mov     ax, SYS_DATA_SEL
        mov     ds, eax
        mov     es, eax
        mov     ss, eax
        lea     rsp, [REL MyStack]

;
; load IDT
;
        lidt    [REL idtr]

        jmp     BlockSignature + 2

%endif

        bits 16

%ifdef LEGACY_A20
Empty8042InputBuffer:
        xor     cx, cx
.Empty8042Loop:
        out     DELAY_PORT, ax          ; Delay 1us
        in      al, KBD_STATUS_PORT     ; Read the 8042 Status Port
        and     al, 2                   ; Check the Input Buffer Full Flag
        loopnz  .Empty8042Loop          ; Loop until the input buffer is empty or a timout of 65536 uS
        ret
%endif

;
; Data
;

        align 2, db 0

gdtr:
        dw GDT_END - GDT_BASE - 1
        dd GDT_BASE

;
; global descriptor table (GDT)
;

        align GDT_DESC_SIZE, db 0

GDT_BASE:
NULL_SEL:               equ $ - GDT_BASE
        times GDT_DESC_SIZE db 0
LINEAR_SEL:             equ $ - GDT_BASE
        GDT_DESC 0x92, 0xCF
LINEAR_CODE_SEL:        equ $ - GDT_BASE
        GDT_DESC 0x9A, 0xCF
SYS_DATA_SEL:           equ $ - GDT_BASE
        GDT_DESC 0x92, 0xCF
SYS_CODE_SEL:           equ $ - GDT_BASE
        GDT_DESC 0x9A, 0xCF
        times GDT_DESC_SIZE db 0
%ifdef X64
SYS_DATA64_SEL:         equ $ - GDT_BASE
        GDT_DESC 0x92, 0xCF
SYS_CODE64_SEL:         equ $ - GDT_BASE
        GDT_DESC 0x9A, 0xAF
%else
        times GDT_DESC_SIZE db 0
%endif
        times GDT_DESC_SIZE db 0
GDT_END:

        align 2, db 0

idtr:
        dw IDT_END - IDT_BASE - 1
        dd IDT_BASE
%ifdef X64
        dd 0
%endif

;
;  interrupt descriptor table (IDT)
;
;
;   Note: The hardware IRQ's specified in this table are the normal PC/AT IRQ
;       mappings.  This implementation only uses the system timer and all other
;       IRQs will remain masked.
;

        align IDT_DESC_SIZE, db 0

IDT_BASE:
%rep 20 ; Exceptions 0 - 19
        IDT_DESC
%endrep
        times 84 * IDT_DESC_SIZE db 0
%rep 16 ; Interrupts IRQ0 - IRQ15 mapped to vectors 0x68 - 0x77
        IDT_DESC
%endrep
        times IDT_DESC_SIZE db 0        ; padding
IDT_END:

        align 4, db 0

MemoryMapSize:
        dd 0
MemoryMap:

        times SIZE_TO_STACK_16 - $ + $$ db 0

MyStack:
; below is the pieces of the IVT that is used to redirect INT 68h - 6fh
;    back to INT 08h - 0fh  when in real mode...  It is 'org'ed to a
;    known low address (20f00) so it can be set up by PlMapIrqToVect in
;    8259.c

%assign i 8
%rep 8
        int i
        iret
%assign i i+1
%endrep

        times   0x1e - $ + MyStack db 0
BlockSignature: 
        dw 0xaa55