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1.1.1.2 ! root 1: ! ! 2: ! SYS_SIZE is the number of clicks (16 bytes) to be loaded. ! 3: ! 0x3000 is 0x30000 bytes = 196kB, more than enough for current ! 4: ! versions of linux ! 5: ! ! 6: SYSSIZE = 0x3000 ! 7: ! ! 8: ! bootsect.s (C) 1991 Linus Torvalds ! 9: ! ! 10: ! bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves ! 11: ! iself out of the way to address 0x90000, and jumps there. ! 12: ! ! 13: ! It then loads 'setup' directly after itself (0x90200), and the system ! 14: ! at 0x10000, using BIOS interrupts. ! 15: ! ! 16: ! NOTE! currently system is at most 8*65536 bytes long. This should be no ! 17: ! problem, even in the future. I want to keep it simple. This 512 kB ! 18: ! kernel size should be enough, especially as this doesn't contain the ! 19: ! buffer cache as in minix ! 20: ! ! 21: ! The loader has been made as simple as possible, and continuos ! 22: ! read errors will result in a unbreakable loop. Reboot by hand. It ! 23: ! loads pretty fast by getting whole sectors at a time whenever possible. 1.1 root 24: 25: .globl begtext, begdata, begbss, endtext, enddata, endbss 26: .text 27: begtext: 28: .data 29: begdata: 30: .bss 31: begbss: 32: .text 33: 1.1.1.2 ! root 34: SETUPLEN = 4 ! nr of setup-sectors ! 35: BOOTSEG = 0x07c0 ! original address of boot-sector ! 36: INITSEG = 0x9000 ! we move boot here - out of the way ! 37: SETUPSEG = 0x9020 ! setup starts here ! 38: SYSSEG = 0x1000 ! system loaded at 0x10000 (65536). ! 39: ENDSEG = SYSSEG + SYSSIZE ! where to stop loading ! 40: ! 41: ! ROOT_DEV: 0x000 - same type of floppy as boot. ! 42: ! 0x301 - first partition on first drive etc ! 43: ROOT_DEV = 0x306 1.1 root 44: 45: entry start 46: start: 47: mov ax,#BOOTSEG 48: mov ds,ax 49: mov ax,#INITSEG 50: mov es,ax 51: mov cx,#256 52: sub si,si 53: sub di,di 54: rep 55: movw 56: jmpi go,INITSEG 57: go: mov ax,cs 58: mov ds,ax 59: mov es,ax 1.1.1.2 ! root 60: ! put stack at 0x9ff00. 1.1 root 61: mov ss,ax 1.1.1.2 ! root 62: mov sp,#0xFF00 ! arbitrary value >>512 1.1 root 63: 1.1.1.2 ! root 64: ! load the setup-sectors directly after the bootblock. ! 65: ! Note that 'es' is already set up. 1.1 root 66: 67: load_setup: 1.1.1.2 ! root 68: mov dx,#0x0000 ! drive 0, head 0 ! 69: mov cx,#0x0002 ! sector 2, track 0 ! 70: mov bx,#0x0200 ! address = 512, in INITSEG ! 71: mov ax,#0x0200+SETUPLEN ! service 2, nr of sectors ! 72: int 0x13 ! read it ! 73: jnc ok_load_setup ! ok - continue 1.1 root 74: mov dx,#0x0000 1.1.1.2 ! root 75: mov ax,#0x0000 ! reset the diskette 1.1 root 76: int 0x13 77: j load_setup 78: 79: ok_load_setup: 80: 1.1.1.2 ! root 81: ! Get disk drive parameters, specifically nr of sectors/track 1.1 root 82: 83: mov dl,#0x00 1.1.1.2 ! root 84: mov ax,#0x0800 ! AH=8 is get drive parameters 1.1 root 85: int 0x13 86: mov ch,#0x00 87: seg cs 88: mov sectors,cx 89: mov ax,#INITSEG 90: mov es,ax 91: 1.1.1.2 ! root 92: ! Print some inane message 1.1 root 93: 1.1.1.2 ! root 94: mov ah,#0x03 ! read cursor pos 1.1 root 95: xor bh,bh 96: int 0x10 97: 98: mov cx,#24 1.1.1.2 ! root 99: mov bx,#0x0007 ! page 0, attribute 7 (normal) 1.1 root 100: mov bp,#msg1 1.1.1.2 ! root 101: mov ax,#0x1301 ! write string, move cursor 1.1 root 102: int 0x10 103: 1.1.1.2 ! root 104: ! ok, we've written the message, now ! 105: ! we want to load the system (at 0x10000) 1.1 root 106: 107: mov ax,#SYSSEG 1.1.1.2 ! root 108: mov es,ax ! segment of 0x010000 1.1 root 109: call read_it 110: call kill_motor 111: 1.1.1.2 ! root 112: ! After that we check which root-device to use. If the device is ! 113: ! defined (!= 0), nothing is done and the given device is used. ! 114: ! Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending ! 115: ! on the number of sectors that the BIOS reports currently. 1.1 root 116: 117: seg cs 118: mov ax,root_dev 119: cmp ax,#0 120: jne root_defined 121: seg cs 122: mov bx,sectors 1.1.1.2 ! root 123: mov ax,#0x0208 ! /dev/ps0 - 1.2Mb 1.1 root 124: cmp bx,#15 125: je root_defined 1.1.1.2 ! root 126: mov ax,#0x021c ! /dev/PS0 - 1.44Mb 1.1 root 127: cmp bx,#18 128: je root_defined 129: undef_root: 130: jmp undef_root 131: root_defined: 132: seg cs 133: mov root_dev,ax 134: 1.1.1.2 ! root 135: ! after that (everyting loaded), we jump to ! 136: ! the setup-routine loaded directly after ! 137: ! the bootblock: 1.1 root 138: 139: jmpi 0,SETUPSEG 140: 1.1.1.2 ! root 141: ! This routine loads the system at address 0x10000, making sure ! 142: ! no 64kB boundaries are crossed. We try to load it as fast as ! 143: ! possible, loading whole tracks whenever we can. ! 144: ! ! 145: ! in: es - starting address segment (normally 0x1000) ! 146: ! ! 147: sread: .word 1+SETUPLEN ! sectors read of current track ! 148: head: .word 0 ! current head ! 149: track: .word 0 ! current track 1.1 root 150: 151: read_it: 152: mov ax,es 153: test ax,#0x0fff 1.1.1.2 ! root 154: die: jne die ! es must be at 64kB boundary ! 155: xor bx,bx ! bx is starting address within segment 1.1 root 156: rp_read: 157: mov ax,es 1.1.1.2 ! root 158: cmp ax,#ENDSEG ! have we loaded all yet? 1.1 root 159: jb ok1_read 160: ret 161: ok1_read: 162: seg cs 163: mov ax,sectors 164: sub ax,sread 165: mov cx,ax 166: shl cx,#9 167: add cx,bx 168: jnc ok2_read 169: je ok2_read 170: xor ax,ax 171: sub ax,bx 172: shr ax,#9 173: ok2_read: 174: call read_track 175: mov cx,ax 176: add ax,sread 177: seg cs 178: cmp ax,sectors 179: jne ok3_read 180: mov ax,#1 181: sub ax,head 182: jne ok4_read 183: inc track 184: ok4_read: 185: mov head,ax 186: xor ax,ax 187: ok3_read: 188: mov sread,ax 189: shl cx,#9 190: add bx,cx 191: jnc rp_read 192: mov ax,es 193: add ax,#0x1000 194: mov es,ax 195: xor bx,bx 196: jmp rp_read 197: 198: read_track: 199: push ax 200: push bx 201: push cx 202: push dx 203: mov dx,track 204: mov cx,sread 205: inc cx 206: mov ch,dl 207: mov dx,head 208: mov dh,dl 209: mov dl,#0 210: and dx,#0x0100 211: mov ah,#2 212: int 0x13 213: jc bad_rt 214: pop dx 215: pop cx 216: pop bx 217: pop ax 218: ret 219: bad_rt: mov ax,#0 220: mov dx,#0 221: int 0x13 222: pop dx 223: pop cx 224: pop bx 225: pop ax 226: jmp read_track 227: 228: /* 229: * This procedure turns off the floppy drive motor, so 230: * that we enter the kernel in a known state, and 231: * don't have to worry about it later. 232: */ 233: kill_motor: 234: push dx 235: mov dx,#0x3f2 236: mov al,#0 237: outb 238: pop dx 239: ret 240: 241: sectors: 242: .word 0 243: 244: msg1: 245: .byte 13,10 246: .ascii "Loading system ..." 247: .byte 13,10,13,10 248: 249: .org 508 250: root_dev: 251: .word ROOT_DEV 252: boot_flag: 253: .word 0xAA55 254: 255: .text 256: endtext: 257: .data 258: enddata: 259: .bss 260: endbss:
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