initial commit

1 files changed, 128 insertions, 0 deletions

diff --git a/boot/bios.inc b/boot/bios.inc
new file mode 100644
index 0000000..ccc94e3
--- /dev/null
+++ b/boot/bios.inc
@@ -0,0 +1,128 @@
+macro bios_a20_enable {
+	mov ax, 0x2401
+	int 0x15
+}
+
+macro bios_vga_write_mode_3 {
+	mov ax, 0x03
+	int 0x10
+}
+
+; assumes dl = drive number
+macro bios_disk_read dst*, cyl*, head*, sector*, count*, err_label* {
+	local read_disk
+
+	assert 0 <= cyl    & cyl    <= 1023
+	assert 0 <= head   & head   <= 15
+	assert 1 <= sector & sector <= 17
+	assert 1 <= count  & count  <= 128
+
+	; try to read disk up to 3 times
+	mov di, 3
+
+read_disk:
+	; ah = 0x02, al = number of sectors to read
+	mov ax, (0x0200 or count)
+
+	; es:bx = pointer to destination buffer
+	if dst = 0
+		xor bx, bx
+	else
+		mov bx, dst
+	end if
+
+	; ch = track/cylinder number, cl = sector number
+	mov cx, ((cyl and 0xff) shl 8) or ((cyl and 0x300) shl 6) or sector
+
+	; dh = head number
+	if head = 0
+		xor dh, dh
+	else
+		mov dh, head
+	end if
+
+	int 0x13
+
+	jc .error
+	cmp ax, count
+	jne .error
+
+	jmp .exit
+.error:
+	dec di
+	jz err_label
+
+	; reset disk on error
+	xor ah, ah
+	stc
+	int 0x13
+	jc err_label
+	jmp read_disk
+.exit:
+}
+
+macro bios_e820_mmap mmap*, err_label* {
+	local e820, e820_entry
+e820:
+	virtual at di
+		label e820_entry
+		.base     dq ?
+		.length   dq ?
+		.type     dd ?
+		.ext_attr dd ?
+		.sizeof = $ - e820_entry
+	end virtual
+
+	mov di, mmap + 4
+	xor ebx, ebx
+	xor bp, bp
+
+	mov edx, 0x0534d4150
+	mov eax, 0xe820
+	mov byte [.ext_attr], 0x01
+	mov ecx, .sizeof
+	int 0x15
+	jc err_label
+
+	mov edx, 0x0534d4150
+	cmp eax, edx
+	jne err_label
+
+	test ebx, ebx
+	jz err_label
+
+	jmp @f
+
+.e820_loop:
+	mov ax, 0xe820
+	mov byte [.ext_attr], 0x01
+	mov ecx, .sizeof
+	int 0x15
+	jc err_label
+
+	mov edx, 0x0534d4150
+@@:
+	jcxz .skip_entry
+
+	; ACPI < 3.0
+	cmp cl, (.sizeof-4)
+	jbe .not_ext
+
+	; ignore data flag
+	test byte [.ext_attr], 0x01
+	jz .skip_entry
+
+.not_ext:
+	mov ecx, dword [.length]
+	or ecx, dword [.length + 4]
+	jz .skip_entry
+
+	inc bp
+	add di, .sizeof
+.skip_entry:
+	test ebx, ebx
+	jnz .e820_loop
+
+	; store e820 mmap entry count at beginning
+	mov [mmap], bp
+}