diff options
Diffstat (limited to 'bootsect.S')
| -rw-r--r-- | bootsect.S | 750 |
1 files changed, 375 insertions, 375 deletions
@@ -1,375 +1,375 @@ -/* - * bootsect.s Copyright (C) 1991, 1992 Linus Torvalds - * - * bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves - * itself out of the way to address 0x90000, and jumps there. - * - * It then loads 'setup' directly after itself (0x90200), and the system - * at 0x10000, using BIOS interrupts. - * - * The loader has been made as simple as possible, and continuos - * read errors will result in a unbreakable loop. Reboot by hand. It - * loads pretty fast by getting whole tracks at a time whenever possible. - * - * 1-Jan-96 Modified by Chris Brady for use as a boot loader for MemTest-86. - */ - -#include "defs.h" - -ROOT_DEV = 0 - -.code16 -.section ".bootsect", "ax", @progbits -_boot: - - -# ld86 requires an entry symbol. This may as well be the usual one. -.globl _main -_main: - movw $BOOTSEG, %ax - movw %ax, %ds - movw $INITSEG, %ax - movw %ax, %es - movw $256, %cx - subw %si, %si - subw %di, %di - cld - rep - movsw - ljmp $INITSEG, $go - _boot - -go: - movw %cs, %ax - movw $(0x4000-12), %dx # 0x4000 is arbitrary value >= length of - # bootsect + length of setup + room for stack - # 12 is disk parm size - -# bde - changed 0xff00 to 0x4000 to use debugger at 0x6400 up (bde). We -# wouldn't have to worry about this if we checked the top of memory. Also -# my BIOS can be configured to put the wini drive tables in high memory -# instead of in the vector table. The old stack might have clobbered the -# drive table. - - movw %ax, %ds - movw %ax, %es - movw %ax, %ss # put stack at INITSEG:0x4000-12. - movw %dx, %sp - -/* - * Many BIOS's default disk parameter tables will not - * recognize multi-sector reads beyond the maximum sector number - * specified in the default diskette parameter tables - this may - * mean 7 sectors in some cases. - * - * Since single sector reads are slow and out of the question, - * we must take care of this by creating new parameter tables - * (for the first disk) in RAM. We will set the maximum sector - * count to 18 - the most we will encounter on an HD 1.44. - * - * High doesn't hurt. Low does. - * - * Segments are as follows: ds=es=ss=cs - INITSEG, - * fs = 0, gs = parameter table segment - */ - pushw $0 - popw %fs - movw $0x78, %bx # fs:bx is parameter table address - lgs %fs:(%bx),%si # gs:si is source - - movw %dx, %di # es:di is destination - movw $6, %cx # copy 12 bytes - cld - - rep movsw %gs:(%si), (%di) - - movw %dx, %di - movb $18, 4(%di) # patch sector count - - movw %di, %fs:(%bx) - movw %es, %fs:2(%bx) - - movw %cs, %ax - movw %ax, %fs - movw %ax, %gs - - xorb %ah, %ah # reset FDC - xorb %dl, %dl - int $0x13 - -# load the setup-sectors directly after the bootblock. -# Note that 'es' is already set up. - -load_setup: - xorw %dx, %dx # drive 0, head 0 - movw $0x0002, %cx # sector 2, track 0 - movw $0x0200, %bx # address = 512, in INITSEG - movw $(0x0200 + SETUPSECS), %ax # service 2, nr of sectors - # (assume all on head 0, track 0) - int $0x13 # read it - jnc ok_load_setup # ok - continue - - pushw %ax # dump error code - call print_nl - movw %sp, %bp - call print_hex - popw %ax - - xorb %dl, %dl # reset FDC - xorb %ah, %ah - int $0x13 - jmp load_setup - -ok_load_setup: - -# Get disk drive parameters, specifically nr of sectors/track - - -/* It seems that there is no BIOS call to get the number of sectors. Guess - * 18 sectors if sector 18 can be read, 15 if sector 15 can be read. - * Otherwise guess 9 - */ - - xorw %dx, %dx # drive 0, head 0 - movw $0x0012, %cx # sector 18, track 0 - movw $(0x200+(SETUPSECS*0x200)), %bx # address after setup (es = cs) - movw $0x0201, %ax # service 2, 1 sector - int $0x13 - jnc got_sectors - movb $0x0f, %cl # sector 15 - movw $0x0201, %ax # service 2, 1 sector - int $0x13 - jnc got_sectors - movb $0x09, %cl - -got_sectors: - movw %cx, %cs:sectors - _boot - movw $INITSEG, %ax - movw %ax, %es - -# Print some inane message - - movb $0x03, %ah # read cursor pos - xorb %bh, %bh - int $0x10 - - movw $9, %cx - movw $0x0007, %bx # page 0, attribute 7 (normal) - movw $msg1 - _boot, %bp - movw $0x1301, %ax # write string, move cursor - int $0x10 - -# ok, we've written the message, now -# we want to load the system (at 0x10000) - - movw $TSTLOAD, %ax - movw %ax, %es # segment of 0x010000 - call read_it - call kill_motor - call print_nl - -# after that (everyting loaded), we jump to -# the setup-routine loaded directly after -# the bootblock: - - ljmp $SETUPSEG,$0 - -# This routine loads the system at address 0x10000, making sure -# no 64kB boundaries are crossed. We try to load it as fast as -# possible, loading whole tracks whenever we can. -# -# in: es - starting address segment (normally 0x1000) -# -sread: .word 1+SETUPSECS # sectors read of current track -head: .word 0 # current head -track: .word 0 # current track - -read_it: - movw %es, %ax - testw $0x0fff, %ax -die: - jne die # es must be at 64kB boundary - xorw %bx,%bx # bx is starting address within segment -rp_read: - movw %es, %ax - subw $TSTLOAD, %ax # have we loaded all yet? - cmpw syssize - _boot, %ax - jbe ok1_read - ret -ok1_read: - movw %cs:sectors - _boot, %ax - subw sread - _boot, %ax - movw %ax, %cx - shlw $9, %cx - addw %bx, %cx - jnc ok2_read - je ok2_read - xorw %ax, %ax - subw %bx, %ax - shrw $9, %ax -ok2_read: - call read_track - movw %ax, %cx - add sread - _boot, %ax - cmpw %cs:sectors - _boot, %ax - jne ok3_read - movw $1, %ax - subw head - _boot, %ax - jne ok4_read - incw track - _boot -ok4_read: - movw %ax, head - _boot - xorw %ax, %ax -ok3_read: - movw %ax, sread - _boot - shlw $9, %cx - addw %cx, %bx - jnc rp_read - movw %es, %ax - addb $0x10, %ah - movw %ax, %es - xorw %bx, %bx - jmp rp_read - -read_track: - pusha - pusha - movw $0xe2e, %ax # loading... message 2e = . - movw $7, %bx - int $0x10 - popa - - movw track - _boot, %dx - movw sread - _boot, %cx - incw %cx - movb %dl, %ch - movw head - _boot, %dx - movb %dl, %dh - andw $0x0100, %dx - movb $2, %ah - - pushw %dx # save for error dump - pushw %cx - pushw %bx - pushw %ax - - int $0x13 - jc bad_rt - addw $8, %sp - popa - ret - -bad_rt: - pushw %ax # save error code - call print_all # ah = error, al = read - - xorb %ah, %ah - xorb %dl, %dl - int $0x13 - - addw $10, %sp - popa - jmp read_track - -/* - * print_all is for debugging purposes. - * It will print out all of the registers. The assumption is that this is - * called from a routine, with a stack frame like - * dx - * cx - * bx - * ax - * error - * ret <- sp - * -*/ - -print_all: - movw $5, %cx # error code + 4 registers - movw %sp, %bp - -print_loop: - pushw %cx # save count left - call print_nl # nl for readability - - cmpb 5, %cl # see if register name is needed - jae no_reg - - movw $(0xe05 + 'A' - 1), %ax - subb %cl, %al - int $0x10 - movb $'X', %al - int $0x10 - movb $':', %al - int $0x10 - -no_reg: - addw $2, %bp # next register - call print_hex # print it - popw %cx - loop print_loop - ret - -print_nl: - movw $0xe0d, %ax # CR - int $0x10 - movb $0x0a, %al # LF - int $0x10 - ret - -/* - * print_hex is for debugging purposes, and prints the word - * pointed to by ss:bp in hexadecmial. -*/ - -print_hex: - movw $4, %cx # 4 hex digits - movw (%bp), %dx # load word into dx - -print_digit: - rolw $4, %dx # rotate so that lowest 4 bits are used - movb $0xe, %ah - movb %dl, %al # mask off so we have only next nibble - andb $0xf, %al - addb $'0', %al # convert to 0-based digit - cmpb $'9', %al # check for overflow - jbe good_digit - addb $('A' - '0' - 10), %al - -good_digit: - int $0x10 - loop print_digit - ret - - -/* - * This procedure turns off the floppy drive motor, so - * that we enter the kernel in a known state, and - * don't have to worry about it later. - */ -kill_motor: - pushw %dx - movw $0x3f2, %dx - xorb %al, %al - outb %al, %dx - popw %dx - ret - -sectors: - .word 0 - -msg1: - .byte 13,10 - .ascii "Loading" - -.org 497 -setup_sects: - .byte SETUPSECS -.org 500 -syssize: - .word _syssize -.org 508 -root_dev: - .word ROOT_DEV -boot_flag: - .word 0xAA55 -_eboot: +/*
+ * bootsect.s Copyright (C) 1991, 1992 Linus Torvalds
+ *
+ * bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
+ * itself out of the way to address 0x90000, and jumps there.
+ *
+ * It then loads 'setup' directly after itself (0x90200), and the system
+ * at 0x10000, using BIOS interrupts.
+ *
+ * The loader has been made as simple as possible, and continuos
+ * read errors will result in a unbreakable loop. Reboot by hand. It
+ * loads pretty fast by getting whole tracks at a time whenever possible.
+ *
+ * 1-Jan-96 Modified by Chris Brady for use as a boot loader for MemTest-86.
+ */
+
+#include "defs.h"
+
+ROOT_DEV = 0
+
+.code16
+.section ".bootsect", "ax", @progbits
+_boot:
+
+
+# ld86 requires an entry symbol. This may as well be the usual one.
+.globl _main
+_main:
+ movw $BOOTSEG, %ax
+ movw %ax, %ds
+ movw $INITSEG, %ax
+ movw %ax, %es
+ movw $256, %cx
+ subw %si, %si
+ subw %di, %di
+ cld
+ rep
+ movsw
+ ljmp $INITSEG, $go - _boot
+
+go:
+ movw %cs, %ax
+ movw $(0x4000-12), %dx # 0x4000 is arbitrary value >= length of
+ # bootsect + length of setup + room for stack
+ # 12 is disk parm size
+
+# bde - changed 0xff00 to 0x4000 to use debugger at 0x6400 up (bde). We
+# wouldn't have to worry about this if we checked the top of memory. Also
+# my BIOS can be configured to put the wini drive tables in high memory
+# instead of in the vector table. The old stack might have clobbered the
+# drive table.
+
+ movw %ax, %ds
+ movw %ax, %es
+ movw %ax, %ss # put stack at INITSEG:0x4000-12.
+ movw %dx, %sp
+
+/*
+ * Many BIOS's default disk parameter tables will not
+ * recognize multi-sector reads beyond the maximum sector number
+ * specified in the default diskette parameter tables - this may
+ * mean 7 sectors in some cases.
+ *
+ * Since single sector reads are slow and out of the question,
+ * we must take care of this by creating new parameter tables
+ * (for the first disk) in RAM. We will set the maximum sector
+ * count to 18 - the most we will encounter on an HD 1.44.
+ *
+ * High doesn't hurt. Low does.
+ *
+ * Segments are as follows: ds=es=ss=cs - INITSEG,
+ * fs = 0, gs = parameter table segment
+ */
+ pushw $0
+ popw %fs
+ movw $0x78, %bx # fs:bx is parameter table address
+ lgs %fs:(%bx),%si # gs:si is source
+
+ movw %dx, %di # es:di is destination
+ movw $6, %cx # copy 12 bytes
+ cld
+
+ rep movsw %gs:(%si), (%di)
+
+ movw %dx, %di
+ movb $18, 4(%di) # patch sector count
+
+ movw %di, %fs:(%bx)
+ movw %es, %fs:2(%bx)
+
+ movw %cs, %ax
+ movw %ax, %fs
+ movw %ax, %gs
+
+ xorb %ah, %ah # reset FDC
+ xorb %dl, %dl
+ int $0x13
+
+# load the setup-sectors directly after the bootblock.
+# Note that 'es' is already set up.
+
+load_setup:
+ xorw %dx, %dx # drive 0, head 0
+ movw $0x0002, %cx # sector 2, track 0
+ movw $0x0200, %bx # address = 512, in INITSEG
+ movw $(0x0200 + SETUPSECS), %ax # service 2, nr of sectors
+ # (assume all on head 0, track 0)
+ int $0x13 # read it
+ jnc ok_load_setup # ok - continue
+
+ pushw %ax # dump error code
+ call print_nl
+ movw %sp, %bp
+ call print_hex
+ popw %ax
+
+ xorb %dl, %dl # reset FDC
+ xorb %ah, %ah
+ int $0x13
+ jmp load_setup
+
+ok_load_setup:
+
+# Get disk drive parameters, specifically nr of sectors/track
+
+
+/* It seems that there is no BIOS call to get the number of sectors. Guess
+ * 18 sectors if sector 18 can be read, 15 if sector 15 can be read.
+ * Otherwise guess 9
+ */
+
+ xorw %dx, %dx # drive 0, head 0
+ movw $0x0012, %cx # sector 18, track 0
+ movw $(0x200+(SETUPSECS*0x200)), %bx # address after setup (es = cs)
+ movw $0x0201, %ax # service 2, 1 sector
+ int $0x13
+ jnc got_sectors
+ movb $0x0f, %cl # sector 15
+ movw $0x0201, %ax # service 2, 1 sector
+ int $0x13
+ jnc got_sectors
+ movb $0x09, %cl
+
+got_sectors:
+ movw %cx, %cs:sectors - _boot
+ movw $INITSEG, %ax
+ movw %ax, %es
+
+# Print some inane message
+
+ movb $0x03, %ah # read cursor pos
+ xorb %bh, %bh
+ int $0x10
+
+ movw $9, %cx
+ movw $0x0007, %bx # page 0, attribute 7 (normal)
+ movw $msg1 - _boot, %bp
+ movw $0x1301, %ax # write string, move cursor
+ int $0x10
+
+# ok, we've written the message, now
+# we want to load the system (at 0x10000)
+
+ movw $TSTLOAD, %ax
+ movw %ax, %es # segment of 0x010000
+ call read_it
+ call kill_motor
+ call print_nl
+
+# after that (everyting loaded), we jump to
+# the setup-routine loaded directly after
+# the bootblock:
+
+ ljmp $SETUPSEG,$0
+
+# This routine loads the system at address 0x10000, making sure
+# no 64kB boundaries are crossed. We try to load it as fast as
+# possible, loading whole tracks whenever we can.
+#
+# in: es - starting address segment (normally 0x1000)
+#
+sread: .word 1+SETUPSECS # sectors read of current track
+head: .word 0 # current head
+track: .word 0 # current track
+
+read_it:
+ movw %es, %ax
+ testw $0x0fff, %ax
+die:
+ jne die # es must be at 64kB boundary
+ xorw %bx,%bx # bx is starting address within segment
+rp_read:
+ movw %es, %ax
+ subw $TSTLOAD, %ax # have we loaded all yet?
+ cmpw syssize - _boot, %ax
+ jbe ok1_read
+ ret
+ok1_read:
+ movw %cs:sectors - _boot, %ax
+ subw sread - _boot, %ax
+ movw %ax, %cx
+ shlw $9, %cx
+ addw %bx, %cx
+ jnc ok2_read
+ je ok2_read
+ xorw %ax, %ax
+ subw %bx, %ax
+ shrw $9, %ax
+ok2_read:
+ call read_track
+ movw %ax, %cx
+ add sread - _boot, %ax
+ cmpw %cs:sectors - _boot, %ax
+ jne ok3_read
+ movw $1, %ax
+ subw head - _boot, %ax
+ jne ok4_read
+ incw track - _boot
+ok4_read:
+ movw %ax, head - _boot
+ xorw %ax, %ax
+ok3_read:
+ movw %ax, sread - _boot
+ shlw $9, %cx
+ addw %cx, %bx
+ jnc rp_read
+ movw %es, %ax
+ addb $0x10, %ah
+ movw %ax, %es
+ xorw %bx, %bx
+ jmp rp_read
+
+read_track:
+ pusha
+ pusha
+ movw $0xe2e, %ax # loading... message 2e = .
+ movw $7, %bx
+ int $0x10
+ popa
+
+ movw track - _boot, %dx
+ movw sread - _boot, %cx
+ incw %cx
+ movb %dl, %ch
+ movw head - _boot, %dx
+ movb %dl, %dh
+ andw $0x0100, %dx
+ movb $2, %ah
+
+ pushw %dx # save for error dump
+ pushw %cx
+ pushw %bx
+ pushw %ax
+
+ int $0x13
+ jc bad_rt
+ addw $8, %sp
+ popa
+ ret
+
+bad_rt:
+ pushw %ax # save error code
+ call print_all # ah = error, al = read
+
+ xorb %ah, %ah
+ xorb %dl, %dl
+ int $0x13
+
+ addw $10, %sp
+ popa
+ jmp read_track
+
+/*
+ * print_all is for debugging purposes.
+ * It will print out all of the registers. The assumption is that this is
+ * called from a routine, with a stack frame like
+ * dx
+ * cx
+ * bx
+ * ax
+ * error
+ * ret <- sp
+ *
+*/
+
+print_all:
+ movw $5, %cx # error code + 4 registers
+ movw %sp, %bp
+
+print_loop:
+ pushw %cx # save count left
+ call print_nl # nl for readability
+
+ cmpb 5, %cl # see if register name is needed
+ jae no_reg
+
+ movw $(0xe05 + 'A' - 1), %ax
+ subb %cl, %al
+ int $0x10
+ movb $'X', %al
+ int $0x10
+ movb $':', %al
+ int $0x10
+
+no_reg:
+ addw $2, %bp # next register
+ call print_hex # print it
+ popw %cx
+ loop print_loop
+ ret
+
+print_nl:
+ movw $0xe0d, %ax # CR
+ int $0x10
+ movb $0x0a, %al # LF
+ int $0x10
+ ret
+
+/*
+ * print_hex is for debugging purposes, and prints the word
+ * pointed to by ss:bp in hexadecmial.
+*/
+
+print_hex:
+ movw $4, %cx # 4 hex digits
+ movw (%bp), %dx # load word into dx
+
+print_digit:
+ rolw $4, %dx # rotate so that lowest 4 bits are used
+ movb $0xe, %ah
+ movb %dl, %al # mask off so we have only next nibble
+ andb $0xf, %al
+ addb $'0', %al # convert to 0-based digit
+ cmpb $'9', %al # check for overflow
+ jbe good_digit
+ addb $('A' - '0' - 10), %al
+
+good_digit:
+ int $0x10
+ loop print_digit
+ ret
+
+
+/*
+ * This procedure turns off the floppy drive motor, so
+ * that we enter the kernel in a known state, and
+ * don't have to worry about it later.
+ */
+kill_motor:
+ pushw %dx
+ movw $0x3f2, %dx
+ xorb %al, %al
+ outb %al, %dx
+ popw %dx
+ ret
+
+sectors:
+ .word 0
+
+msg1:
+ .byte 13,10
+ .ascii "Loading"
+
+.org 497
+setup_sects:
+ .byte SETUPSECS
+.org 500
+syssize:
+ .word _syssize
+.org 508
+root_dev:
+ .word ROOT_DEV
+boot_flag:
+ .word 0xAA55
+_eboot:
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