startup.s

有助于了解操作系统如何启动之过程

	movl	%esp, %ebp

	pushl	%ebx
	pushl	%edi
	pushl	%esi

	/* set up CHS information */

	/* set %ch to low eight bits of cylinder */
	xchgb	%cl, %ch
	/* set bits 6-7 of %cl to high two bits of cylinder */
	shlb	$6, %cl
	/* set bits 0-5 of %cl to sector */
	addb	0xc(%ebp), %cl
	/* set %dh to head */
	movb	0x8(%ebp), %dh
	/* set %ah to AH */
	movb	%al, %ah
	/* set %al to NSEC */
	movb	0x10(%ebp), %al
	/* save %ax in %di */
	movw	%ax, %di
	/* save SEGMENT in %bx */
	movw	0x14(%ebp), %bx
		
	/* enter real mode */
	call	prot_to_real

	.code16
	movw	%bx, %es
	xorw	%bx, %bx
	movw	$3, %si		/* attempt at least three times */

1:	
	movw	%di, %ax
	int	$0x13		/* do the operation */
	jnc	2f		/* check if successful */

	movb	%ah, %bl	/* save return value */
	/* if fail, reset the disk system */
	xorw	%ax, %ax
	int	$0x13
	
	decw	%si
	cmpw	$0, %si
	je	2f
	xorb	%bl, %bl
	jmp	1b		/* retry */
2:	
	/* back to protected mode */
	DATA32	call	real_to_prot
	.code32

	movb	%bl, %al	/* return value in %eax */
	
	popl	%esi
	popl	%edi
	popl	%ebx
	popl	%ebp

	ret	$(4 * 4)


/*
 *   int grub_biosdisk_check_int13_extensions (int drive)
 *
 *   Check if LBA is supported for DRIVE. If it is supported, then return
 *   the major version of extensions, otherwise zero.
 */

FUNCTION(grub_biosdisk_check_int13_extensions)
	pushl	%ebp
	pushl	%ebx

	/* drive */
	movb	%al, %dl
	/* enter real mode */
	call	prot_to_real

	.code16
	movb	$0x41, %ah
	movw	$0x55aa, %bx
	int	$0x13		/* do the operation */
	
	/* check the result */
	jc	1f
	cmpw	$0xaa55, %bx
	jne	1f

	movb	%ah, %bl	/* save the major version into %bl */

	/* check if AH=0x42 is supported */
	andw	$1, %cx
	jnz	2f
	
1:
	xorb	%bl, %bl
2:
	/* back to protected mode */
	DATA32	call	real_to_prot
	.code32

	movb	%bl, %al	/* return value in %eax */

	popl	%ebx
	popl	%ebp

	ret


/*
 *   int grub_biosdisk_get_diskinfo_int13_extensions (int drive, void *drp)
 *
 *   Return the geometry of DRIVE in a drive parameters, DRP. If an error
 *   occurs, then return non-zero, otherwise zero.
 */

FUNCTION(grub_biosdisk_get_diskinfo_int13_extensions)
	pushl	%ebp
	pushl	%ebx
	pushl	%esi

	/* compute the address of drive parameters */
	movw	%dx, %si
	xorw	%dx, %dx
	shrl	$4, %edx
	movw	%dx, %bx	/* save the segment into %bx */
	/* drive */
	movb	%al, %dl
	/* enter real mode */
	call	prot_to_real

	.code16
	movb	$0x48, %ah
	movw	%bx, %ds
	int	$0x13		/* do the operation */
	movb	%ah, %bl	/* save return value in %bl */
	/* clear the data segment */
	xorw	%ax, %ax
	movw	%ax, %ds
	/* back to protected mode */
	DATA32	call	real_to_prot
	.code32

	movb	%bl, %al	/* return value in %eax */

	popl	%esi
	popl	%ebx
	popl	%ebp
	
	ret


/*
 *   int grub_biosdisk_get_diskinfo_standard (int drive,
 *                                            unsigned long *cylinders, 
 *                                            unsigned long *heads,
 *                                            unsigned long *sectors)
 *
 *   Return the geometry of DRIVE in CYLINDERS, HEADS and SECTORS. If an
 *   error occurs, then return non-zero, otherwise zero.
 */

FUNCTION(grub_biosdisk_get_diskinfo_standard)
	pushl	%ebp
	pushl	%ebx
	pushl	%edi

	/* push CYLINDERS */
	pushl	%edx
	/* push HEADS */
	pushl	%ecx
	/* SECTORS is on the stack */
	
	/* drive */
	movb	%al, %dl
	/* enter real mode */
	call	prot_to_real

	.code16
	movb	$0x8, %ah
	int	$0x13		/* do the operation */
	/* check if successful */
	testb	%ah, %ah
	jnz	1f
	/* bogus BIOSes may not return an error number */
	testb	$0x3f, %cl	/* 0 sectors means no disk */
	jnz	1f		/* if non-zero, then succeed */
	/* XXX 0x60 is one of the unused error numbers */
	movb	$0x60, %ah
1:
	movb	%ah, %bl	/* save return value in %bl */
	/* back to protected mode */
	DATA32	call	real_to_prot
	.code32

	/* pop HEADS */
	popl	%edi
	movb	%dh, %al
	incl	%eax	/* the number of heads is counted from zero */
	movl	%eax, (%edi)

	/* pop CYLINDERS */
	popl	%edi
	movb	%ch, %al
	movb	%cl, %ah
	shrb	$6, %ah	/* the number of cylinders is counted from zero */
	incl	%eax
	movl	%eax, (%edi)

	/* SECTORS */
	movl	0x10(%esp), %edi
	andb	$0x3f, %cl
	movzbl	%cl, %eax
	movl	%eax, (%edi)
	
	xorl	%eax, %eax
	movb	%bl, %al	/* return value in %eax */

	popl	%edi
	popl	%ebx
	popl	%ebp

	ret	$4


/*
 * int grub_biosdisk_get_num_floppies (void)
 */
FUNCTION(grub_biosdisk_get_num_floppies)
	pushl	%ebp

	xorl	%edx, %edx
	call	prot_to_real
	
	.code16
	/* reset the disk system first */
	int	$0x13
1:
	stc
	
	/* call GET DISK TYPE */
	movb	$0x15, %ah
	int	$0x13

	jc	2f

	/* check if this drive exists */	
	testb	$0x3, %ah
	jz	2f

	incb	%dl
	cmpb	$2, %dl
	jne	1b
2:
	DATA32	call	real_to_prot
	.code32

	movl	%edx, %eax
	popl	%ebp
	ret
	
	
/*
 *
 * grub_get_memsize(i) :  return the memory size in KB. i == 0 for conventional
 *		memory, i == 1 for extended memory
 *	BIOS call "INT 12H" to get conventional memory size
 *	BIOS call "INT 15H, AH=88H" to get extended memory size
 *		Both have the return value in AX.
 *
 */

FUNCTION(grub_get_memsize)
	pushl	%ebp

	movl	%eax, %edx

	call	prot_to_real	/* enter real mode */
	.code16

	testl	%edx, %edx
	jnz	xext

	int	$0x12
	jmp	xdone

xext:
	movb	$0x88, %ah
	int	$0x15

xdone:
	movw	%ax, %dx

	DATA32	call	real_to_prot
	.code32

	movw	%dx, %ax

	popl	%ebp
	ret


/*
 *
 * grub_get_eisa_mmap() :  return packed EISA memory map, lower 16 bits is
 *		memory between 1M and 16M in 1K parts, upper 16 bits is
 *		memory above 16M in 64K parts.  If error, return zero.
 *	BIOS call "INT 15H, AH=E801H" to get EISA memory map,
 *		AX = memory between 1M and 16M in 1K parts.
 *		BX = memory above 16M in 64K parts.
 *
 */

FUNCTION(grub_get_eisa_mmap)
	pushl	%ebp
	pushl	%ebx

	call	prot_to_real	/* enter real mode */
	.code16

	movw	$0xe801, %ax
	int	$0x15

	shll	$16, %ebx
	movw	%ax, %bx

	DATA32	call	real_to_prot
	.code32

	cmpb	$0x86, %bh
	je	xnoteisa

	movl	%ebx, %eax

xnoteisa:
	popl	%ebx
	popl	%ebp
	ret

/*
 *
 * grub_get_mmap_entry(addr, cont) : address and old continuation value (zero to
 *		start), for the Query System Address Map BIOS call.
 *
 *  Sets the first 4-byte int value of "addr" to the size returned by
 *  the call.  If the call fails, sets it to zero.
 *
 *	Returns:  new (non-zero) continuation value, 0 if done.
 */

FUNCTION(grub_get_mmap_entry)
	pushl	%ebp
	pushl	%ebx
	pushl	%edi
	pushl	%esi

	/* push ADDR */
	pushl	%eax
	
	/* place address (+4) in ES:DI */
	addl	$4, %eax
	movl	%eax, %edi
	andl	$0xf, %edi
	shrl	$4, %eax
	movl	%eax, %esi

	/* set continuation value */
	movl	%edx, %ebx

	/* set default maximum buffer size */
	movl	$0x14, %ecx

	/* set EDX to 'SMAP' */
	movl	$0x534d4150, %edx

	call	prot_to_real	/* enter real mode */
	.code16

	movw	%si, %es
	movl	$0xe820, %eax
	int	$0x15

	DATA32	jc	xnosmap

	cmpl	$0x534d4150, %eax
	jne	xnosmap

	cmpl	$0x14, %ecx
	jl	xnosmap

	cmpl	$0x400, %ecx
	jg	xnosmap

	jmp	xsmap

xnosmap:
	xorl	%ecx, %ecx

xsmap:
	DATA32	call	real_to_prot
	.code32

	/* write length of buffer (zero if error) into ADDR */
	popl	%eax
	movl	%ecx, (%eax)

	/* set return value to continuation */
	movl	%ebx, %eax

	popl	%esi
	popl	%edi
	popl	%ebx
	popl	%ebp
	ret

	
/*
 * void grub_console_real_putchar (int c)
 *
 * Put the character C on the console. Because GRUB wants to write a
 * character with an attribute, this implementation is a bit tricky.
 * If C is a control character (CR, LF, BEL, BS), use INT 10, AH = 0Eh
 * (TELETYPE OUTPUT). Otherwise, save the original position, put a space,
 * save the current position, restore the original position, write the
 * character and the attribute, and restore the current position.
 *
 * The reason why this is so complicated is that there is no easy way to
 * get the height of the screen, and the TELETYPE OUTPUT BIOS call doesn't
 * support setting a background attribute.
 */
FUNCTION(grub_console_real_putchar)
	movl	%eax, %edx
	pusha
	movb	EXT_C(grub_console_cur_color), %bl
	
	call	prot_to_real
	.code16
	movb	%dl, %al
	xorb	%bh, %bh

	/* use teletype output if control character */
	cmpb	$0x7, %al
	je	1f
	cmpb	$0x8, %al
	je	1f
	cmpb	$0xa, %al
	je	1f
	cmpb	$0xd, %al
	je	1f

	/* save the character and the attribute on the stack */
	pushw	%ax
	pushw	%bx
	
	/* get the current position */
	movb	$0x3, %ah
	int	$0x10

	/* check the column with the width */
	cmpb	$79, %dl
	jl	2f
	
	/* print CR and LF, if next write will exceed the width */	
	movw	$0x0e0d, %ax
	int	$0x10
	movb	$0x0a, %al
	int	$0x10
	
	/* get the current position */
	movb	$0x3, %ah
	int	$0x10

2:	
	/* restore the character and the attribute */
	popw	%bx
	popw	%ax
	
	/* write the character with the attribute */
	movb	$0x9, %ah
	movw	$1, %cx
	int	$0x10

	/* move the cursor forward */
	incb	%dl
	movb	$0x2, %ah
	int	$0x10

	jmp	3f

1:	movw	$1, %bx
	movb	$0xe, %ah
	int	$0x10
	
3:	DATA32	call	real_to_prot
	.code32
	
	popa
	ret
	

/*
 * int grub_console_getkey (void)
 * BIOS call "INT 16H Function 00H" to read character from keyboard
 *	Call with	%ah = 0x0
 *	Return:		%ah = keyboard scan code
 *			%al = ASCII character
 */

/* this table is used in translate_keycode below */
translation_table:
	.word	GRUB_CONSOLE_KEY_LEFT, 2
	.word	GRUB_CONSOLE_KEY_RIGHT, 6
	.word	GRUB_CONSOLE_KEY_UP, 16
	.word	GRUB_CONSOLE_KEY_DOWN, 14
	.word	GRUB_CONSOLE_KEY_HOME, 1
	.word	GRUB_CONSOLE_KEY_END, 5
	.word	GRUB_CONSOLE_KEY_DC, 4
	.word	GRUB_CONSOLE_KEY_BACKSPACE, 8
	.word	GRUB_CONSOLE_KEY_PPAGE, 7
	.word	GRUB_CONSOLE_KEY_NPAGE, 3
	.word	0
	
/*
 * translate_keycode translates the key code %dx to an ascii code.
 */
	.code16

translate_keycode:
	pushw	%bx
	pushw	%si
	
	movw	$ABS(translation_table), %si
	
1:	lodsw
	/* check if this is the end */
	testw	%ax, %ax
	jz	2f
	/* load the ascii code into %ax */
	movw	%ax, %bx
	lodsw
	/* check if this matches the key code */
	cmpw	%bx, %dx
	jne	1b
	/* translate %dx, if successful */
	movw	%ax, %dx

2:	popw	%si
	popw	%bx
	ret

	.code32
	
FUNCTION(grub_console_getkey)
	pushl	%ebp

	call	prot_to_real
	.code16

	int	$0x16

	movw	%ax, %dx		/* real_to_prot uses %eax */
	call	translate_keycode
		
	DATA32	call	real_to_prot
	.code32

	movw	%dx, %ax

	popl	%ebp
	ret


/*
 * int grub_console_checkkey (void)
 *	if there is a character pending, return it; otherwise return -1
 * BIOS call "INT 16H Function 01H" to check whether a character is pending
 *	Call with	%ah = 0x1
 *	Return:
 *		If key waiting to be input:
 *			%ah = keyboard scan code
 *			%al = ASCII character
 *			Zero flag = clear
 *		else
 *			Zero flag = set
 */
FUNCTION(grub_console_checkkey)
	pushl	%ebp
	xorl	%edx, %edx
	
	call	prot_to_real	/* enter real mode */
	.code16

	movb	$0x1, %ah
	int	$0x16

	jz	notpending
	
	movw	%ax, %dx
	DATA32	jmp	pending

notpending:
	decl	%edx

pending:
	DATA32	call	real_to_prot
	.code32

	movl	%edx, %eax

	popl	%ebp
	ret

	
/*
 * grub_uint16_t grub_console_getxy (void)
 * BIOS call "INT 10H Function 03h" to get cursor position
 *	Call with	%ah = 0x03
 *			%bh = page
 *      Returns         %ch = starting scan line
 *                      %cl = ending scan line
 *                      %dh = row (0 is top)
 *                      %dl = column (0 is left)
 */


FUNCTION(grub_console_getxy)
	pushl	%ebp
	pushl	%ebx                    /* save EBX */

	call	prot_to_real
	.code16

        xorb	%bh, %bh                /* set page to 0 */
	movb	$0x3, %ah
	int	$0x10			/* get cursor position */

	DATA32	call	real_to_prot
	.code32

	movb	%dl, %ah
	movb	%dh, %al

	popl	%ebx
	popl	%ebp
	ret


/*
 * void grub_console_gotoxy(grub_uint8_t x, grub_uint8_t y)
 * BIOS call "INT 10H Function 02h" to set cursor position
 *	Call with	%ah = 0x02
 *			%bh = page
 *                      %dh = row (0 is top)
 *                      %dl = column (0 is left)
 */


FUNCTION(grub_console_gotoxy)
	pushl	%ebp
	pushl	%ebx                    /* save EBX */

	movb	%dl, %dh	/* %dh = y */
	movb	%al, %dl	/* %dl = x */