# Stage 2 — loaded by stage1 at 0x7E00, still in 16-bit real mode. Does the
# VBE mode setup, A20 line, and real->protected mode switch that used to
# live directly in the boot sector, then hands off to stage2main() (C) to
# draw a splash and load the actual kernel. Not sector-size-constrained —
# only bounded by STAGE2_SECTORS in bootasm.S / the Makefile.
#include "../include/asm.h"
#include "../include/memlayout.h"
#include "../include/mmu.h"

.code16
.global stage2start
stage2start:
  # Segments are already zeroed by stage1; %sp is inherited too.

  movw    $bootmsg, %si
  call    print16

  # VBE Setup. Mode info block goes at 0x30000, not 0x9000 — stage2 itself
  # is loaded starting at 0x7E00 and, with the boot-menu/progress-bar code,
  # is now big enough to reach 0x9000, so writing the VBE block there would
  # clobber stage2's own tail end. 0x30000 is clear of stage2 (ends well
  # under 0xA000), the multiboot kernel-search buffer (0x10000-0x14000),
  # and the kernel's own load address (0x100000).
  movw    $0x3000, %ax
  movw    %ax, %es
  xorw    %di, %di            # ES:DI = 3000:0000 = flat 0x30000
  movw    $0x0143, %cx
  movw    $0x4F01, %ax
  int     $0x10

  cmpw    $0x004F, %ax
  jne     e820
  movw    $0x4143, %bx
  movw    $0x4F02, %ax
  int     $0x10

  # BIOS E820 memory map — the standard firmware interface every serious
  # loader (GRUB, Linux's own boot stub, the BSDs) uses to learn the real
  # RAM layout instead of guessing. Entry count goes to flat 0x30200,
  # 24-byte entries start at 0x30208 (both inside the 0x3000 segment the
  # VBE block already claimed; verbose flag sits at +0x100). Capped at 32
  # entries so a pathological BIOS can't run us past the buffer.
e820:
  movw    $0x3000, %ax
  movw    %ax, %es
  xorl    %ebx, %ebx          # continuation cookie, 0 = first call
  movw    $0x208, %di
  xorl    %ebp, %ebp          # entry count
e820loop:
  movl    $0xE820, %eax
  movl    $0x534D4150, %edx   # 'SMAP'
  movl    $24, %ecx
  int     $0x15
  jc      e820done            # carry = end of map (or unsupported BIOS)
  cmpl    $0x534D4150, %eax
  jne     e820done
  addw    $24, %di
  incl    %ebp
  cmpl    $32, %ebp
  jae     e820done
  testl   %ebx, %ebx
  jnz     e820loop
e820done:
  movl    %ebp, %es:(0x200)
  xorw    %ax, %ax
  movw    %ax, %es

seta20.1:
  inb     $0x64, %al
  testb   $0x2, %al
  jnz     seta20.1
  movb    $0xd1, %al
  outb    %al, $0x64
seta20.2:
  inb     $0x64, %al
  testb   $0x2, %al
  jnz     seta20.2
  movb    $0xdf, %al
  outb    %al, $0x60

  lgdt    gdtdesc
  movl    %cr0, %eax
  orl     $CR0_PE, %eax
  movl    %eax, %cr0

  ljmp    $(SEG_KCODE<<3), $start32

# Print null-terminated string at DS:SI via BIOS teletype (real mode only).
# Clobbers AX, BX, SI.
print16:
.Lp16loop:
  lodsb
  testb   %al, %al
  jz      .Lp16done
  movb    $0x0E, %ah
  movw    $0x0007, %bx
  int     $0x10
  jmp     .Lp16loop
.Lp16done:
  ret

bootmsg:
  .asciz "SchOS booting...\r\n"

.code32
start32:
  movw    $(SEG_KDATA<<3), %ax
  movw    %ax, %ds
  movw    %ax, %es
  movw    %ax, %ss
  xorw    %ax, %ax
  movw    %ax, %fs
  movw    %ax, %gs

  movl    $0x7c00, %esp
  call    stage2main

spin:
  jmp     spin

.p2align 2
gdt:
  SEG_NULLASM
  SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff)
  SEG_ASM(STA_W, 0x0, 0xffffffff)

gdtdesc:
  .word   (gdtdesc - gdt - 1)
  .long   gdt