setup.S负责从 BIOS 获取系统数据，并将它们放入系统内存中的适当位置。
其他引导加载程序，如 GNU GRUB 和 LILO，也可以加载 bzImage。这些引导加载程序应将 bzImage 加载到内存中，并设置“实模式内核头”，特别是 type_of_loader，然后将控制权直接传递给 bsetup。setup.S假设
bsetup 或 setup 可能未加载到 SETUPSEG:0，即当控制权传递给 时，CS 可能不等于 SETUPSEGsetup.S;
setup 的前 4 个扇区紧跟在 bootsect 之后加载。其余部分可以加载到 SYSSEG:0，位于 vmlinux 之前；此假设不适用于 bsetup。
/* Signature words to ensure LILO loaded us right */
#define SIG1 0xAA55
#define SIG2 0x5A5A
INITSEG = DEF_INITSEG # 0x9000, we move boot here, out of the way
SYSSEG = DEF_SYSSEG # 0x1000, system loaded at 0x10000 (65536).
SETUPSEG = DEF_SETUPSEG # 0x9020, this is the current segment
# ... and the former contents of CS
DELTA_INITSEG = SETUPSEG - INITSEG # 0x0020
.code16
.text
///////////////////////////////////////////////////////////////////////////////
start:
{
goto trampoline(); // skip the following header
}
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
.ascii "HdrS" # header signature
.word 0x0203 # header version number (>= 0x0105)
# or else old loadlin-1.5 will fail)
realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
start_sys_seg: .word SYSSEG
.word kernel_version # pointing to kernel version string
# above section of header is compatible
# with loadlin-1.5 (header v1.5). Don't
# change it.
// kernel_version defined below
type_of_loader: .byte 0 # = 0, old one (LILO, Loadlin,
# Bootlin, SYSLX, bootsect...)
# See Documentation/i386/boot.txt for
# assigned ids
# flags, unused bits must be zero (RFU) bit within loadflags
loadflags:
LOADED_HIGH = 1 # If set, the kernel is loaded high
CAN_USE_HEAP = 0x80 # If set, the loader also has set
# heap_end_ptr to tell how much
# space behind setup.S can be used for
# heap purposes.
# Only the loader knows what is free
#ifndef __BIG_KERNEL__
.byte 0
#else
.byte LOADED_HIGH
#endif
setup_move_size: .word 0x8000 # size to move, when setup is not
# loaded at 0x90000. We will move setup
# to 0x90000 then just before jumping
# into the kernel. However, only the
# loader knows how much data behind
# us also needs to be loaded.
code32_start: # here loaders can put a different
# start address for 32-bit code.
#ifndef __BIG_KERNEL__
.long 0x1000 # 0x1000 = default for zImage
#else
.long 0x100000 # 0x100000 = default for big kernel
#endif
ramdisk_image: .long 0 # address of loaded ramdisk image
# Here the loader puts the 32-bit
# address where it loaded the image.
# This only will be read by the kernel.
ramdisk_size: .long 0 # its size in bytes
bootsect_kludge:
.word bootsect_helper, SETUPSEG
heap_end_ptr: .word modelist+1024 # (Header version 0x0201 or later)
# space from here (exclusive) down to
# end of setup code can be used by setup
# for local heap purposes.
// modelist is at the end of .text section
pad1: .word 0
cmd_line_ptr: .long 0 # (Header version 0x0202 or later)
# If nonzero, a 32-bit pointer
# to the kernel command line.
# The command line should be
# located between the start of
# setup and the end of low
# memory (0xa0000), or it may
# get overwritten before it
# gets read. If this field is
# used, there is no longer
# anything magical about the
# 0x90000 segment; the setup
# can be located anywhere in
# low memory 0x10000 or higher.
ramdisk_max: .long __MAXMEM-1 # (Header version 0x0203 or later)
# The highest safe address for
# the contents of an initrd |
__MAXMEM 定义在linux/asm-i386/page.h:
/* * A __PAGE_OFFSET of 0xC0000000 means that the kernel has * a virtual address space of one gigabyte, which limits the * amount of physical memory you can use to about 950MB. */ #define __PAGE_OFFSET (0xC0000000) /* * This much address space is reserved for vmalloc() and iomap() * as well as fixmap mappings. */ #define __VMALLOC_RESERVE (128 << 20) #define __MAXMEM (-__PAGE_OFFSET-__VMALLOC_RESERVE) |
setup 头部必须遵循一定的布局模式。请参考linux/Documentation/i386/boot.txt:
Offset Proto Name Meaning /Size 0200/2 2.00+ jump Jump instruction 0202/4 2.00+ header Magic signature "HdrS" 0206/2 2.00+ version Boot protocol version supported 0208/4 2.00+ realmode_swtch Boot loader hook 020C/2 2.00+ start_sys The load-low segment (0x1000) (obsolete) 020E/2 2.00+ kernel_version Pointer to kernel version string 0210/1 2.00+ type_of_loader Boot loader identifier 0211/1 2.00+ loadflags Boot protocol option flags 0212/2 2.00+ setup_move_size Move to high memory size (used with hooks) 0214/4 2.00+ code32_start Boot loader hook 0218/4 2.00+ ramdisk_image initrd load address (set by boot loader) 021C/4 2.00+ ramdisk_size initrd size (set by boot loader) 0220/4 2.00+ bootsect_kludge DO NOT USE - for bootsect.S use only 0224/2 2.01+ heap_end_ptr Free memory after setup end 0226/2 N/A pad1 Unused 0228/4 2.02+ cmd_line_ptr 32-bit pointer to the kernel command line 022C/4 2.03+ initrd_addr_max Highest legal initrd address |
由于 setup 代码可能不是连续的，我们应该首先检查代码完整性。
///////////////////////////////////////////////////////////////////////////////
trampoline()
{
start_of_setup(); // never return
.space 1024;
}
///////////////////////////////////////////////////////////////////////////////
// check signature to see if all code loaded
start_of_setup()
{
// Bootlin depends on this being done early, check bootlin:technic.doc
int13/AH=15h(AL=0, DL=0x81);
// int13/AH=15h: DISK - GET DISK TYPE
#ifdef SAFE_RESET_DISK_CONTROLLER
int13/AH=0(AL=0, DL=0x80);
// int13/AH=00h: DISK - RESET DISK SYSTEM
#endif
DS = CS;
// check signature at end of setup
if (setup_sig1!=SIG1 || setup_sig2!=SIG2) {
goto bad_sig;
}
goto goodsig1;
}
///////////////////////////////////////////////////////////////////////////////
// some small functions
prtstr(); /* print asciiz string at DS:SI */
prtsp2(); /* print double space */
prtspc(); /* print single space */
prtchr(); /* print ascii in AL */
beep(); /* print CTRL-G, i.e. beep */ |
如果未找到签名，则其余 setup 代码可能位于 SYSSEG:0 的 vmlinux 之前。
no_sig_mess: .string "No setup signature found ..."
goodsig1:
goto goodsig; // make near jump
///////////////////////////////////////////////////////////////////////////////
// move the rest setup code from SYSSEG:0 to CS:0800
bad_sig()
DELTA_INITSEG = 0x0020 (= SETUPSEG - INITSEG)
SYSSEG = 0x1000
word start_sys_seg = SYSSEG; // defined in setup header
{
DS = CS - DELTA_INITSEG; // aka INITSEG
BX = (byte)(DS:[497]); // i.e. setup_sects
// first 4 sectors already loaded
CX = (BX - 4) << 8; // rest code in word (2-bytes)
start_sys_seg = (CX >> 3) + SYSSEG; // real system code start
move SYSSEG:0 to CS:0800 (CX*2 bytes);
if (setup_sig1!=SIG1 || setup_sig2!=SIG2) {
no_sig:
prtstr("No setup signature found ...");
no_sig_loop:
hlt;
goto no_sig_loop;
}
} |
setup 代码已移动到正确的位置。变量 start_sys_seg 指向实际系统代码的起始位置。如果未发生 "bad_sig"，start_sys_seg 仍为 SYSSEG。
检查加载程序是否与镜像兼容。
///////////////////////////////////////////////////////////////////////////////
good_sig()
char loadflags; // in setup header
char type_of_loader; // in setup header
LOADHIGH = 1
{
DS = CS - DELTA_INITSEG; // aka INITSEG
if ( (loadflags & LOADHIGH) && !type_of_loader ) {
// Nope, old loader tries to load big-kernel
prtstr("Wrong loader, giving up...");
goto no_sig_loop; // defined above in bad_sig()
}
}
loader_panic_mess: .string "Wrong loader, giving up..." |
尝试三种不同的内存检测方案，以 KB 为单位获取扩展内存大小（大于 1M）。
首先，尝试 e820h，它可以让我们组装内存映射；然后尝试 e801h，它返回 32 位内存大小；最后是 88h，它返回 0-64M。
///////////////////////////////////////////////////////////////////////////////
// get memory size
loader_ok()
E820NR = 0x1E8
E820MAP = 0x2D0
{
// when entering this function, DS = CS-DELTA_INITSEG, aka INITSEG
(long)DS:[0x1E0] = 0;
#ifndef STANDARD_MEMORY_BIOS_CALL
(byte)DS:[0x1E8] = 0; // E820NR
/* method E820H: see ACPI spec
* the memory map from hell. e820h returns memory classified into
* a whole bunch of different types, and allows memory holes and
* everything. We scan through this memory map and build a list
* of the first 32 memory areas, which we return at [E820MAP]. */
meme820:
EBX = 0;
DI = 0x02D0; // E820MAP
do {
jmpe820:
int15/EAX=E820h(EDX='SMAP', EBX, ECX=20, ES:DI=DS:DI);
// int15/AX=E820h: GET SYSTEM MEMORY MAP
if (failed || 'SMAP'!=EAX) break;
// if (1!=DS:[DI+16]) continue; // not usable
good820:
if (DS:[1E8]>=32) break; // entry# > E820MAX
DS:[0x1E8]++; // entry# ++;
DI += 20; // adjust buffer for next
again820:
} while (!EBX) // not finished
bail820:
/* method E801H:
* memory size is in 1k chunksizes, to avoid confusing loadlin.
* we store the 0xe801 memory size in a completely different place,
* because it will most likely be longer than 16 bits.
* (use 1e0 because that's what Larry Augustine uses in his
* alternative new memory detection scheme, and it's sensible
* to write everything into the same place.) */
meme801:
stc; // to work around buggy BIOSes
CX = DX = 0;
int15/AX=E801h;
/* int15/AX=E801h: GET MEMORY SIZE FOR >64M CONFIGURATIONS
* AX = extended memory between 1M and 16M, in K (max 3C00 = 15MB)
* BX = extended memory above 16M, in 64K blocks
* CX = configured memory 1M to 16M, in K
* DX = configured memory above 16M, in 64K blocks */
if (failed) goto mem88;
if (!CX && !DX) {
CX = AX;
DX = BX;
}
e801usecxdx:
(long)DS:[0x1E0] = ((EDX & 0xFFFF) << 6) + (ECX & 0xFFFF); // in K
#endif
mem88: // old traditional method
int15/AH=88h;
/* int15/AH=88h: SYSTEM - GET EXTENDED MEMORY SIZE
* AX = number of contiguous KB starting at absolute address 100000h */
DS:[2] = AX;
} |
检查硬件支持，如键盘、视频适配器、硬盘、MCA 总线和 pointing device。
{
// set the keyboard repeat rate to the max
int16/AX=0305h(BX=0);
// int16/AH=03h: KEYBOARD - SET TYPEMATIC RATE AND DELAY
/* Check for video adapter and its parameters and
* allow the user to browse video modes. */
video(); // see video.S
// get hd0 and hd1 data
copy hd0 data (*int41) to CS-DELTA_INITSEG:0080 (16 bytes);
// int41: SYSTEM DATA - HARD DISK 0 PARAMETER TABLE ADDRESS
copy hd1 data (*int46) to CS-DELTA_INITSEG:0090 (16 bytes);
// int46: SYSTEM DATA - HARD DISK 1 PARAMETER TABLE ADDRESS
// check if hd1 exists
int13/AH=15h(AL=0, DL=0x81);
// int13/AH=15h: DISK - GET DISK TYPE
if (failed || AH!=03h) { // AH==03h if it is a hard disk
no_disk1:
clear CS-DELTA_INITSEG:0090 (16 bytes);
}
is_disk1:
// check for Micro Channel (MCA) bus
CS-DELTA_INITSEG:[0xA0] = 0; // set table length to 0
int15/AH=C0h;
/* int15/AH=C0h: SYSTEM - GET CONFIGURATION
* ES:BX = ROM configuration table */
if (failed) goto no_mca;
move ROM configuration table (ES:BX) to CS-DELTA_INITSEG:00A0;
// CX = (table length<14)? CX:16; first 16 bytes only
no_mca:
// check for PS/2 pointing device
CS-DELTA_INITSEG:[0x1FF] = 0; // default is no pointing device
int11h();
// int11h: BIOS - GET EQUIPMENT LIST
if (AL & 0x04) { // mouse installed
DS:[0x1FF] = 0xAA;
}
} |
检查 BIOS APM 支持。
#if defined(CONFIG_APM) || defined(CONFIG_APM_MODULE)
{
DS:[0x40] = 0; // version = 0 means no APM BIOS
int15/AX=5300h(BX=0);
// int15/AX=5300h: Advanced Power Management v1.0+ - INSTALLATION CHECK
if (failed || 'PM'!=BX || !(CX & 0x02)) goto done_apm_bios;
// (CX & 0x02) means 32 bit is supported
int15/AX=5304h(BX=0);
// int15/AX=5304h: Advanced Power Management v1.0+ - DISCONNECT INTERFACE
EBX = CX = DX = ESI = DI = 0;
int15/AX=5303h(BX=0);
/* int15/AX=5303h: Advanced Power Management v1.0+
* - CONNECT 32-BIT PROTMODE INTERFACE */
if (failed) {
no_32_apm_bios: // I moved label no_32_apm_bios here
DS:[0x4C] &= ~0x0002; // remove 32 bit support bit
goto done_apm_bios;
}
DS:[0x42] = AX, 32-bit code segment base address;
DS:[0x44] = EBX, offset of entry point;
DS:[0x48] = CX, 16-bit code segment base address;
DS:[0x4A] = DX, 16-bit data segment base address;
DS:[0x4E] = ESI, APM BIOS code segment length;
DS:[0x52] = DI, APM BIOS data segment length;
int15/AX=5300h(BX=0); // check again
// int15/AX=5300h: Advanced Power Management v1.0+ - INSTALLATION CHECK
if (success && 'PM'==BX) {
DS:[0x40] = AX, APM version;
DS:[0x4C] = CX, APM flags;
} else {
apm_disconnect:
int15/AX=5304h(BX=0);
/* int15/AX=5304h: Advanced Power Management v1.0+
* - DISCONNECT INTERFACE */
}
done_apm_bios:
}
#endif |
// call mode switch
{
if (realmode_swtch) {
realmode_swtch(); // mode switch hook
} else {
rmodeswtch_normal:
default_switch() {
cli; // no interrupts allowed
outb(0x80, 0x70); // disable NMI
}
}
rmodeswtch_end:
}
// relocate code if necessary
{
(long)code32 = code32_start;
if (!(loadflags & LOADED_HIGH)) { // low loaded zImage
// 0x0100 <= start_sys_seg < CS-DELTA_INITSEG
do_move0:
AX = 0x100;
BP = CS - DELTA_INITSEG; // aka INITSEG
BX = start_sys_seg;
do_move:
move system image from (start_sys_seg:0 .. CS-DELTA_INITSEG:0)
to 0100:0; // move 0x1000 bytes each time
}
end_move: |
然后，如有必要，它会将代码从 CS-DELTA_INITSEG:0 (bbootsect 和 bsetup) 重定位到 INITSEG:0。
DS = CS; // aka SETUPSEG
// Check whether we need to be downward compatible with version <=201
if (!cmd_line_ptr && 0x20!=type_of_loader && SETUPSEG!=CS) {
cli; // as interrupt may use stack when we are moving
// store new SS in DX
AX = CS - DELTA_INITSEG;
DX = SS;
if (DX>=AX) { // stack frame will be moved together
DX = DX + INITSEG - AX; // i.e. SS-CS+SETUPSEG
}
move_self_1:
/* move CS-DELTA_INITSEG:0 to INITSEG:0 (setup_move_size bytes)
* in two steps in order not to overwrite code on CS:IP
* move up (src < dest) but downward ("std") */
move CS-DELTA_INITSEG:move_self_here+0x200
to INITSEG:move_self_here+0x200,
setup_move_size-(move_self_here+0x200) bytes;
// INITSEG:move_self_here+0x200 == SETUPSEG:move_self_here
goto SETUPSEG:move_self_here; // CS=SETUPSEG now
move_self_here:
move CS-DELTA_INITSEG:0 to INITSEG:0,
move_self_here+0x200 bytes; // I mean old CS before goto
DS = SETUPSEG;
SS = DX;
}
end_move_self:
} |
有关 A20 问题和解决方案，请参阅 A20 - 过去的痛苦。
A20_TEST_LOOPS = 32 # Iterations per wait
A20_ENABLE_LOOPS = 255 # Total loops to try
{
#if defined(CONFIG_MELAN)
// Enable A20. AMD Elan bug fix.
outb(0x02, 0x92); // outb(val, port)
a20_elan_wait:
while (!a20_test()); // test not passed
goto a20_done;
#endif
a20_try_loop:
// First, see if we are on a system with no A20 gate.
a20_none:
if (a20_test()) goto a20_done; // test passed
// Next, try the BIOS (INT 0x15, AX=0x2401)
a20_bios:
int15/AX=2401h;
// Int15/AX=2401h: SYSTEM - later PS/2s - ENABLE A20 GATE
if (a20_test()) goto a20_done; // test passed
// Try enabling A20 through the keyboard controller
a20_kbc:
empty_8042();
if (a20_test()) goto a20_done; // test again in case BIOS delayed
outb(0xD1, 0x64); // command write
empty_8042();
outb(0xDF, 0x60); // A20 on
empty_8042();
// wait until a20 really *is* enabled
a20_kbc_wait:
CX = 0;
a20_kbc_wait_loop:
do {
if (a20_test()) goto a20_done; // test passed
} while (--CX)
// Final attempt: use "configuration port A"
outb((inb(0x92) | 0x02) & 0xFE, 0x92);
// wait for configuration port A to take effect
a20_fast_wait:
CX = 0;
a20_fast_wait_loop:
do {
if (a20_test()) goto a20_done; // test passed
} while (--CX)
// A20 is still not responding. Try frobbing it again.
if (--a20_tries) goto a20_try_loop;
prtstr("linux: fatal error: A20 gate not responding!");
a20_die:
hlt;
goto a20_die;
}
a20_tries:
.byte A20_ENABLE_LOOPS // i.e. 255
a20_err_msg:
.ascii "linux: fatal error: A20 gate not responding!"
.byte 13, 10, 0 |
为了确保代码与所有 32 位 IA-32 处理器的兼容性，请执行以下步骤切换到保护模式
准备 GDT，在第一个 GDT 条目中包含一个空描述符，一个代码段描述符和一个数据段描述符；
禁用中断，包括可屏蔽硬件中断和 NMI；
使用 "lgdt" 指令将 GDT 的基地址和限长加载到 GDTR 寄存器；
使用 "mov cr0" (Intel 386 及更高版本) 或 "lmsw" 指令 (与 Intel 286 兼容) 在 CR0 寄存器中设置 PE 标志；
立即执行远 "jmp" 或远 "call" 指令。
a20_done:
{
lidt idt_48; // load idt with 0, 0;
// convert DS:gdt to a linear ptr
*(long*)(gdt_48+2) = DS << 4 + &gdt;
lgdt gdt_48;
// reset coprocessor
outb(0, 0xF0);
delay();
outb(0, 0xF1);
delay();
// reprogram the interrupts
outb(0xFF, 0xA1); // mask all interrupts
delay();
outb(0xFB, 0x21); // mask all irq's but irq2 which is cascaded
// protected mode!
AX = 1;
lmsw ax; // machine status word, bit 0 thru 15 of CR0
// only affects PE, MP, EM & TS flags
goto flush_instr;
flush_instr:
BX = 0; // flag to indicate a boot
ESI = (CS - DELTA_INITSEG) << 4; // pointer to real-mode code
/* NOTE: For high loaded big kernels we need a
* jmpi 0x100000,__KERNEL_CS
*
* but we yet haven't reloaded the CS register, so the default size
* of the target offset still is 16 bit.
* However, using an operand prefix (0x66), the CPU will properly
* take our 48 bit far pointer. (INTeL 80386 Programmer's Reference
* Manual, Mixing 16-bit and 32-bit code, page 16-6) */
// goto __KERNEL_CS:[(uint32*)code32]; */
.byte 0x66, 0xea
code32: .long 0x1000 // overwritten in Section 4.7
.word __KERNEL_CS // segment 0x10
// see linux/arch/i386/boot/compressed/head.S:startup_32
} |
控制权传递给 linux/arch/i386/boot/compressed/head.S:startup_32。对于 zImage，地址为 0x1000；对于 bzImage，地址为 0x100000。请参阅 第 5 节。
ESI 指向收集的系统数据的内存区域。它用于将参数从内核的 16 位实模式代码传递到 32 位部分。请参阅linux/Documentation/i386/zero-page.txt了解详情。
有关模式切换的详细信息，请参阅 IA-32 手册 Vol.3。(第 9.8 节. 保护模式操作的软件初始化，第 9.9.1 节. 切换到保护模式，以及第 17.4 节. 在混合大小代码段之间传输控制权)。
其余是支持函数和变量。
/* macros created by linux/Makefile targets:
* include/linux/compile.h and include/linux/version.h */
kernel_version: .ascii UTS_RELEASE
.ascii " ("
.ascii LINUX_COMPILE_BY
.ascii "@"
.ascii LINUX_COMPILE_HOST
.ascii ") "
.ascii UTS_VERSION
.byte 0
///////////////////////////////////////////////////////////////////////////////
default_switch() { cli; outb(0x80, 0x70); } /* disable interrupts and NMI */
bootsect_helper(ES:BX); /* see Section 3.7 */
///////////////////////////////////////////////////////////////////////////////
a20_test()
{
FS = 0;
GS = 0xFFFF;
CX = A20_TEST_LOOPS; // i.e. 32
AX = FS:[0x200];
do {
a20_test_wait:
FS:[0x200] = ++AX;
delay();
} while (AX==GS:[0x210] && --CX);
return (AX!=GS[0x210]);
// ZF==0 (i.e. NZ/NE, a20_test!=0) means test passed
}
///////////////////////////////////////////////////////////////////////////////
// check that the keyboard command queue is empty
empty_8042()
{
int timeout = 100000;
for (;;) {
empty_8042_loop:
if (!--timeout) return;
delay();
inb(0x64, &AL); // 8042 status port
if (AL & 1) { // has output
delay();
inb(0x60, &AL); // read it
no_output: } else if (!(AL & 2)) return; // no input either
}
}
///////////////////////////////////////////////////////////////////////////////
// read the CMOS clock, return the seconds in AL, used in video.S
gettime()
{
int1A/AH=02h();
/* int1A/AH=02h: TIME - GET REAL-TIME CLOCK TIME
* DH = seconds in BCD */
AL = DH & 0x0F;
AH = DH >> 4;
aad;
}
///////////////////////////////////////////////////////////////////////////////
delay() { outb(AL, 0x80); } // needed after doing I/O
// Descriptor table
gdt:
.word 0, 0, 0, 0 # dummy
.word 0, 0, 0, 0 # unused
// segment 0x10, __KERNEL_CS
.word 0xFFFF # 4Gb - (0x100000*0x1000 = 4Gb)
.word 0 # base address = 0
.word 0x9A00 # code read/exec
.word 0x00CF # granularity = 4096, 386
# (+5th nibble of limit)
// segment 0x18, __KERNEL_DS
.word 0xFFFF # 4Gb - (0x100000*0x1000 = 4Gb)
.word 0 # base address = 0
.word 0x9200 # data read/write
.word 0x00CF # granularity = 4096, 386
# (+5th nibble of limit)
idt_48:
.word 0 # idt limit = 0
.word 0, 0 # idt base = 0L
/* [gdt_48] should be 0x0800 (2048) to match the comment,
* like what Linux 2.2.22 does. */
gdt_48:
.word 0x8000 # gdt limit=2048,
# 256 GDT entries
.word 0, 0 # gdt base (filled in later)
#include "video.S"
// signature at the end of setup.S:
{
setup_sig1: .word SIG1 // 0xAA55
setup_sig2: .word SIG2 // 0x5A5A
modelist:
} |
视频设置和检测代码在video.S:
ASK_VGA = 0xFFFD // defined in linux/include/asm-i386/boot.h
///////////////////////////////////////////////////////////////////////////////
video()
{
pushw DS; // use different segments
FS = DS;
DS = ES = CS;
GS = 0;
cld;
basic_detect(); // basic adapter type testing (EGA/VGA/MDA/CGA)
#ifdef CONFIG_VIDEO_SELECT
if (FS:[0x01FA]!=ASK_VGA) { // user selected video mode
mode_set();
if (failed) {
prtstr("You passed an undefined mode number.\n");
mode_menu();
}
} else {
vid2: mode_menu();
}
vid1:
#ifdef CONFIG_VIDEO_RETAIN
restore_screen(); // restore screen contents
#endif /* CONFIG_VIDEO_RETAIN */
#endif /* CONFIG_VIDEO_SELECT */
mode_params(); // store mode parameters
popw ds; // restore original DS
} |