X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?a=blobdiff_plain;f=src%2Fboot%2Fboot2.s;h=161bd7343373334d3cc9905fa2ddfd09a98f7af3;hb=eb934abaf0dcfa48589c6ac15f2a2ff235c5aea0;hp=47121ee70f6443544581ad88dcca61d8f8d53d23;hpb=098b0dd7bf6600ed6b904cd531a55a6415996900;p=bootcensus diff --git a/src/boot/boot2.s b/src/boot/boot2.s index 47121ee..161bd73 100644 --- a/src/boot/boot2.s +++ b/src/boot/boot2.s @@ -1,36 +1,553 @@ +# pcboot - bootable PC demo/game kernel +# Copyright (C) 2018 John Tsiombikas +# +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY, without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . + # this is the second-stage boot loader .code16 .section .boot2,"a" + .set main_load_addr, 0x100000 + + # make sure any BIOS call didn't re-enable interrupts + cli + + # enter unreal mode + call unreal + + movb $10, %al + call ser_putchar + + call clearscr + + # enable A20 address line + call enable_a20 + + # load the whole program into memory starting at 1MB + call load_main + mov $0x13, %ax int $0x10 - pushw $63 - pushw $63 - pushw $0 - pushw $0xff - call set_palette - add $8, %sp + # load initial GDT + lgdt (gdt_lim) + # load initial IDT + lidt (idt_lim) + + # enter protected mode for the first time + mov %cr0, %eax + or $1, %eax + mov %eax, %cr0 + # inter-segment jump to set cs selector to segment 1 + ljmp $0x8,$0f + + .code32 + # set all data selectors to segment 2 +0: mov $0x10, %ax + mov %ax, %ds + mov %ax, %ss + mov %ax, %es + mov %ax, %gs + mov %ax, %fs + + jmp main_load_addr + + cli +0: hlt + jmp 0b + + + + .align 4 +gdt_lim: .word 23 +gdt_base:.long gdt + + .align 4 +idt_lim: .word 111 +idt_base:.long idt + + + .align 8 +gdt: # 0: null segment + .long 0 + .long 0 + # 1: code - base:0, lim:4g, G:4k, 32bit, avl, pres|app, dpl:0, type:code/non-conf/rd + .long 0x0000ffff + .long 0x00cf9a00 + # 2: data - base:0, lim:4g, G:4k, 32bit, avl, pres|app, dpl:0, type:data/rw + .long 0x0000ffff + .long 0x00cf9200 + + + .align 8 +idt: .space 104 + # trap gate 13: general protection fault + .short prot_fault + .short 0x8 + # type: trap, present, default + .short 0x8f00 + .short 0 + +gpf_msg: .asciz "GP fault " + +prot_fault: + mov (%esp), %eax + shr $3, %eax + call print_num + mov $64, %al + call putchar + mov 4(%esp), %eax + call print_num + mov $10, %al + call putchar + hlt + + .code16 +unreal: + # use the same GDT above, will use data segment: 2 + lgdt (gdt_lim) + + mov %cr0, %eax + or $1, %ax + mov %eax, %cr0 + jmp 0f + +0: mov $0x10, %ax + mov %ax, %ds + mov %ax, %es + mov %ax, %fs + mov %ax, %gs + mov %ax, %ss + + mov %cr0, %eax + and $0xfffe, %ax + mov %eax, %cr0 + + xor %ax, %ax + mov %ax, %ds + mov %ax, %es + mov %ax, %fs + mov %ax, %gs + mov %ax, %ss + ret + +mainsz_msg: .asciz "Main program size: " +mainsz_msg2: .asciz " (" +mainsz_msg3: .asciz " sectors)\n" + +first_sect: .long 0 +sect_left: .long 0 +cur_track: .long 0 +trk_sect: .long 0 +dest_ptr: .long 0 + +load_main: + movl $main_load_addr, dest_ptr + + # calculate first sector + mov $_boot2_size, %eax + add $511, %eax + shr $9, %eax + # add 1 to account for the boot sector + inc %eax + mov %eax, first_sect + + # calculate the first track (first_sect / sect_per_track) + movzxw sect_per_track, %ecx + xor %edx, %edx + div %ecx + mov %eax, cur_track + # remainder is sector within track + mov %edx, trk_sect + + mov $mainsz_msg, %esi + call putstr + mov $_main_size, %eax + mov %eax, %ecx + call print_num + + mov $mainsz_msg2, %esi + call putstr + + # calculate sector count + add $511, %eax + shr $9, %eax + mov %eax, sect_left + + call print_num + mov $mainsz_msg3, %esi + call putstr + + # read a whole track into the buffer (or partial first track) +ldloop: + movzxw sect_per_track, %ecx + sub trk_sect, %ecx + push %ecx + call read_track + + mov buffer, %eax + call print_num + mov $10, %al + call putchar + + # copy to high memory + mov $buffer, %esi + mov dest_ptr, %edi + mov (%esp), %ecx + shl $9, %ecx + add %ecx, dest_ptr + shr $2, %ecx + addr32 rep movsl + + incl cur_track + # other than the first track which might be partial, all the rest start from 0 + movl $0, trk_sect + + pop %ecx + sub %ecx, sect_left + ja ldloop - pushw $0xa000 - pop %es - xor %di, %di - mov $16000, %ecx - mov $0xffffffff, %eax - rep stosl + # the BIOS might have enabled interrupts + cli + # just in case we were loaded from floppy, turn all floppy motors off + mov $0x3f2, %dx + in %dx, %al + and $0xf0, %al + out %al, %dx + + mov $10, %ax + call putchar + + # DBG hlt -set_palette: - mov %sp, %bp - mov $0x3c8, %dx - movw 2(%bp), %ax - outb %al, %dx - inc %dx - movw 4(%bp), %ax - outb %al, %dx - movw 6(%bp), %ax - outb %al, %dx - movw 8(%bp), %ax - outb %al, %dx ret + +rdtrk_msg: .asciz "Reading track: " +rdcyl_msg: .asciz " - cyl: " +rdhead_msg: .asciz " head: " +rdsect_msg: .asciz " start sect: " + +read_retries: .short 0 + + .set drive_number, 0x7bec +read_track: + # set es to the start of the destination buffer to allow reading in + # full 64k chunks if necessary + mov $buffer, %bx + shr $4, %bx + mov %bx, %es + xor %ebx, %ebx + + movw $3, read_retries + +read_try: + # print track + mov $rdtrk_msg, %esi + call putstr + mov cur_track, %eax + call print_num + mov $rdcyl_msg, %esi + call putstr + + # calc cylinder (cur_track / num_heads) and head (cur_track % num_heads) + mov cur_track, %eax + movzxw num_heads, %ecx + xor %edx, %edx + div %ecx + + # print cylinder + push %eax + call print_num + # print head + mov $rdhead_msg, %esi + call putstr + movzx %dx, %eax + call print_num + pop %eax + + # head in dh + mov %dl, %dh + + # cylinder low byte at ch and high bits at cl[7, 6] + mov %al, %ch + mov %ah, %cl + and $3, %cl + ror $2, %cl + + # print start sector + mov $rdsect_msg, %esi + call putstr + mov trk_sect, %eax + call print_num + mov $10, %al + call putchar + + # start sector (1-based) in cl[0, 5] + mov trk_sect, %al + inc %al + and $0x3f, %al + or %al, %cl + + # number of sectors in al + mov 2(%esp), %ax + # call number (2) in ah + mov $2, %ah + # drive number in dl + movb drive_number, %dl + int $0x13 + jnc read_ok + + # abort after 3 attempts + decw read_retries + jz read_fail + + # error, reset controller and retry + xor %ah, %ah + int $0x13 + jmp read_try + +read_fail: + jmp abort_read + +read_ok: + mov $35, %ax + call putchar + + # reset es to 0 before returning + xor %ax, %ax + mov %ax, %es + ret + +str_read_error: .asciz "Read error while reading track: " + +abort_read: + mov $str_read_error, %esi + call putstr + mov cur_track, %eax + call print_num + mov $10, %al + call putchar + + cli +0: hlt + jmp 0b + + + + # better print routines, since we're not constrainted by the 512b of + # the boot sector. +cursor_x: .long 0 +cursor_y: .long 0 + +putchar: + pusha + call ser_putchar + + cmp $10, %al + jnz 0f + call video_newline + jmp 1f + +0: push %eax + mov cursor_y, %eax + mov $80, %ecx + mul %ecx + add cursor_x, %eax + mov %eax, %ebx + pop %eax + + mov $0xb8000, %edx + + # this looks retarded. in nasm: [ebx * 2 + edx] + mov %al, (%edx, %ebx, 2) + movb $7, 1(%edx, %ebx, 2) + incl cursor_x + cmpl $80, cursor_x + jnz 1f + call video_newline + +1: popa + ret + + # expects string pointer in esi +putstr: + mov (%esi), %al + cmp $0, %al + jz 0f + call putchar + inc %esi + jmp putstr +0: ret + + # expects number in eax +print_num: + # save registers + pusha + + mov $numbuf + 16, %esi + movb $0, (%esi) + mov $10, %ebx +convloop: + xor %edx, %edx + div %ebx + add $48, %dl + dec %esi + mov %dl, (%esi) + cmp $0, %eax + jnz convloop + + call putstr + + # restore regs + popa + ret + + +video_newline: + movl $0, cursor_x + incl cursor_y + cmpl $25, cursor_y + jnz 0f + call scrollup + decl cursor_y +0: ret + +scrollup: + pusha + # move 80 * 24 lines from b80a0 -> b8000 + mov $0xb8000, %edi + mov $0xb80a0, %esi + mov $960, %ecx + addr32 rep movsl + # clear last line (b8f00) + mov $0xb8f00, %edi + xor %eax, %eax + mov $40, %ecx + addr32 rep stosl + popa + ret + +clearscr: + mov $0xb8000, %edi + xor %eax, %eax + mov $1000, %ecx + addr32 rep stosl + ret + + .set UART_DATA, 0x3f8 + .set UART_LSTAT, 0x3fd + .set LST_TREG_EMPTY, 0x20 + +ser_putchar: + push %dx + + cmp $10, %al + jnz 0f + push %ax + mov $13, %al + call ser_putchar + pop %ax + +0: mov %al, %ah + # wait until the transmit register is empty + mov $UART_LSTAT, %dx +wait: in %dx, %al + and $LST_TREG_EMPTY, %al + jz wait + mov $UART_DATA, %dx + mov %ah, %al + out %al, %dx + + pop %dx + ret + + + +ena20_msg: .asciz "A20 line enabled\n" + +enable_a20: + call test_a20 + jnc a20done + call enable_a20_kbd + call test_a20 + jnc a20done + call enable_a20_fast + call test_a20 + jnc a20done + # keep trying ... we can't do anything useful without A20 anyway + jmp enable_a20 +a20done: + mov $ena20_msg, %esi + call putstr + ret + + # CF = 1 if A20 test fails (not enabled) +test_a20: + mov $0x07c000, %ebx + mov $0x17c000, %edx + movl $0xbaadf00d, (%ebx) + movl $0xaabbcc42, (%edx) + subl $0xbaadf00d, (%ebx) + ret + + # enable A20 line through port 0x92 (fast A20) +enable_a20_fast: + mov $ena20_fast_msg, %esi + call putstr + + in $0x92, %al + or $2, %al + out %al, $0x92 + ret + +ena20_fast_msg: .asciz "Attempting fast A20 enable\n" + + + # enable A20 line through the keyboard controller + .set KBC_DATA_PORT, 0x60 + .set KBC_CMD_PORT, 0x64 + .set KBC_STATUS_PORT, 0x64 + .set KBC_CMD_RD_OUTPORT, 0xd0 + .set KBC_CMD_WR_OUTPORT, 0xd1 + + .set KBC_STAT_OUT_RDY, 0x01 + .set KBC_STAT_IN_FULL, 0x02 + +enable_a20_kbd: + mov $ena20_kbd_msg, %esi + call putstr + + call kbc_wait_write + mov $KBC_CMD_WR_OUTPORT, %al + out %al, $KBC_CMD_PORT + call kbc_wait_write + mov $0xdf, %al + out %al, $KBC_DATA_PORT + ret + +ena20_kbd_msg: .asciz "Attempting KBD A20 enable\n" + + # wait until the keyboard controller is ready to accept another byte +kbc_wait_write: + in $KBC_STATUS_PORT, %al + and $KBC_STAT_IN_FULL, %al + jnz kbc_wait_write + ret + +numbuf: .space 16 + + .align 16 +buffer: