X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=blobdiff_plain;f=src%2Fboot%2Fboot2.s;h=53dff6d218d37786870d0f34df567f8dd19162c5;hp=e4088f4ccb9e0b50fcfde6cd68b6052aef7d69bc;hb=81c11bdd80190ec319a82b0402173cfb65fcbf72;hpb=11db15bb0f0f3d23aa9b2966c2f65a0379246813 diff --git a/src/boot/boot2.s b/src/boot/boot2.s index e4088f4..53dff6d 100644 --- a/src/boot/boot2.s +++ b/src/boot/boot2.s @@ -1,4 +1,4 @@ -# pcboot - bootable PC demo/game kernel +# 256boss - bootable launcher for 256byte intros # Copyright (C) 2018 John Tsiombikas # # This program is free software: you can redistribute it and/or modify @@ -15,14 +15,23 @@ # along with this program. If not, see . # this is the second-stage boot loader +# plus some other code that needs to run below 1mb (int86 implementation). + .code16 .section .boot2,"ax" .set main_load_addr, 0x100000 + .set drive_number, 0x7bec # make sure any BIOS call didn't re-enable interrupts cli + xor %eax, %eax + mov drive_number, %al + mov %eax, boot_drive_number + + call setup_serial + # enter unreal mode call unreal @@ -34,12 +43,12 @@ # enable A20 address line call enable_a20 + # detect available memory + call detect_memory + # load the whole program into memory starting at 1MB call load_main - #mov $0x13, %ax - #int $0x10 - # load initial GDT lgdt (gdt_lim) # load initial IDT @@ -222,11 +231,15 @@ ldloop: # the BIOS might have enabled interrupts cli - # just in case we were loaded from floppy, turn all floppy motors off + # if we were loaded from floppy, turn all floppy motors off + movb drive_number, %bl + and $0x80, %bl + jnz 0f mov $0x3f2, %dx in %dx, %al - and $0xf0, %al + and $0xf, %al out %al, %dx +0: mov $10, %ax call putchar @@ -243,7 +256,6 @@ rdfail_msg: .asciz "failed\n" 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 @@ -446,15 +458,52 @@ scrollup: clearscr: mov $0xb8000, %edi - xor %eax, %eax + # clear with white-on-black spaces + mov $0x07200720, %eax mov $1000, %ecx addr32 rep stosl ret .set UART_DATA, 0x3f8 + .set UART_DIVLO, 0x3f8 + .set UART_DIVHI, 0x3f9 + .set UART_FIFO, 0x3fa + .set UART_LCTL, 0x3fb + .set UART_MCTL, 0x3fc .set UART_LSTAT, 0x3fd + .set DIV_9600, 115200 / 9600 + .set LCTL_8N1, 0x03 + .set LCTL_DLAB, 0x80 + .set FIFO_ENABLE_CLEAR, 0x07 + .set MCTL_DTR_RTS_OUT2, 0x0b .set LST_TREG_EMPTY, 0x20 +setup_serial: + # set clock divisor + mov $LCTL_DLAB, %al + mov $UART_LCTL, %dx + out %al, %dx + mov $DIV_9600, %ax + mov $UART_DIVLO, %dx + out %al, %dx + shr $8, %ax + mov $UART_DIVHI, %dx + out %al, %dx + # set format 8n1 + mov $LCTL_8N1, %al + mov $UART_LCTL, %dx + out %al, %dx + # clear and enable fifo + mov $FIFO_ENABLE_CLEAR, %al + mov $UART_FIFO, %dx + out %al, %dx + # assert RTS and DTR + mov $MCTL_DTR_RTS_OUT2, %al + mov $UART_MCTL, %dx + out %al, %dx + ret + + ser_putchar: push %dx @@ -554,97 +603,200 @@ kbc_wait_write: numbuf: .space 16 -# this is not boot loader code. It's called later on by the main kernel -# code in 32bit protected mode. It's placed here because it needs to be -# located in base memory as it returns and runs in real mode. - .code32 - .align 4 - # place to save the protected mode IDTR pseudo-descriptor - # with sidt, so that it can be restored before returning - .short 0 -saved_idtr: -idtlim: .short 0 -idtaddr:.long 0 - # real mode IDTR pseudo-descriptor pointing to the IVT at addr 0 - .short 0 -rmidt: .short 0x3ff - .long 0 +detect_memory: + mov $memdet_e820_msg, %esi + call putstr + call detect_mem_e820 + jnc memdet_done + mov $rdfail_msg, %esi + call putstr -saved_esp: .long 0 -saved_ebp: .long 0 + mov $memdet_e801_msg, %esi + call putstr + call detect_mem_e801 + jnc memdet_done + mov $rdfail_msg, %esi + call putstr - # drop back to unreal mode to call 16bit interrupt - .global int86 -int86: - push %ebp - mov %esp, %ebp - pushal - cli - # save protected mode IDTR and replace it with the real mode vectors - sidt (saved_idtr) - lidt (rmidt) + mov $memdet_88_msg, %esi + call putstr + call detect_mem_88 + jnc memdet_done + mov $rdfail_msg, %esi + call putstr - # long jump to load code selector for 16bit code (6) - ljmp $0x30,$0f -0: - .code16 - # disable protection - mov %cr0, %eax - and $0xfffe, %ax - mov %eax, %cr0 - # load cs <- 0 - ljmp $0,$0f -0: # zero data segments - xor %ax, %ax - mov %ax, %ds - mov %ax, %es - mov %ax, %ss - nop + # just panic... + mov $memdet_fail_msg, %esi + call putstr +0: hlt + jmp 0b - # modify the int instruction - mov $int_op, %ebx - movb 4(%ebp), %al - movb %al, 1(%ebx) +memdet_done: + mov $rdok_msg, %esi + call putstr + ret - # load registers from the int86regs struct - mov %esp, saved_esp - mov %ebp, saved_ebp - mov 8(%ebp), %esp - popal - mov saved_esp, %esp +memdet_fail_msg: .ascii "Failed to detect available memory!\n" + .ascii "Please file a bug report: https://github.com/jtsiomb/pcboot/issues\n" + .asciz " or contact me through email: nuclear@member.fsf.org\n" +memdet_e820_msg: .asciz "Detecting RAM (BIOS 15h/0xe820)... " +memdet_e801_msg: .asciz "Detecting RAM (BIOS 15h/0xe801)... " +memdet_88_msg: .asciz "Detecting RAM (BIOS 15h/0x88, max 64mb)... " - # call 16bit interrupt -int_op: int $0 + # detect extended memory using BIOS call 15h/e820 +detect_mem_e820: + movl $0, boot_mem_map_size - mov saved_ebp, %ebp - mov 8(%ebp), %esp - add $32, %esp - pushal - mov saved_esp, %esp + mov $buffer, %edi + xor %ebx, %ebx + mov $0x534d4150, %edx + +e820_looptop: + mov $0xe820, %eax + mov $24, %ecx + int $0x15 + jc e820_fail + cmp $0x534d4150, %eax + jnz e820_fail + + # skip areas starting above 4GB as we won't be able to use them + cmpl $0, 4(%edi) + jnz e820_skip + + # only care for type 1 (usable ram), otherwise ignore + cmpl $1, 16(%edi) + jnz e820_skip + + mov buffer, %eax + mov $boot_mem_map, %esi + mov boot_mem_map_size, %ebp + # again, that's [ebp * 8 + esi] + mov %eax, (%esi,%ebp,8) + + # skip areas with 0 size (also clamp size to 4gb) + # test high 32bits + cmpl $0, 12(%edi) + jz e820_highzero + # high part is non-zero, make low part ffffffff + xor %eax, %eax + not %eax + jmp 0f - # re-enable protection - mov %cr0, %eax - or $1, %ax - mov %eax, %cr0 - # long jump to load code selector for 32bit code (1) - ljmp $0x8,$0f -0: - .code32 - # set data selector (2) to all segment regs - mov $0x10, %ax - mov %ax, %ds - mov %ax, %es - mov %ax, %ss - nop +e820_highzero: + # if both high and low parts are zero, ignore + mov 8(%edi), %eax + cmpl $0, %eax + jz e820_skip - # restore 32bit interrupt descriptor table - lidt (saved_idtr) - sti - popal - pop %ebp +0: mov %eax, 4(%esi,%ebp,8) + incl boot_mem_map_size + +e820_skip: + # terminate the loop if ebx was reset to 0 + cmp $0, %ebx + jz e820_done + jmp e820_looptop + +e820_done: + clc ret +e820_fail: + # if size > 0, then it's not a failure, just the end + cmpl $0, boot_mem_map_size + jnz e820_done + + stc + ret + + + # detect extended memory using BIOS call 15h/e801 +detect_mem_e801: + mov $boot_mem_map, %esi + mov boot_mem_map_size, %ebp + movl $0, (%ebp) + + xor %cx, %cx + xor %dx, %dx + mov $0xe801, %ax + int $0x15 + jc e801_fail + + cmp $0, %cx + jnz 0f + cmp $0, %ax + jz e801_fail + mov %ax, %cx + mov %bx, %dx + +0: movl $0x100000, (%esi) + movzx %cx, %eax + # first size is in KB, convert to bytes + shl $10, %eax + jnc 0f + # overflow means it's >4GB, clamp to 4GB + mov $0xffffffff, %eax +0: mov %eax, 4(%esi) + incl boot_mem_map_size + cmp $0, %dx + jz e801_done + movl $0x1000000, 8(%esi) + movzx %dx, %eax + # second size is in 64kb blocks, convert to bytes + shl $16, %eax + jnc 0f + # overflow means it's >4GB, clamp to 4GB + mov $0xffffffff, %eax +0: mov %eax, 12(%esi) + incl boot_mem_map_size +e801_done: + clc + ret +e801_fail: + stc + ret + +detect_mem_88: + # reportedly some BIOS implementations fail to clear CF on success + clc + mov $0x88, %ah + int $0x15 + jc x88_fail + + cmp $0, %ax + jz x88_fail + + # ax has size in KB, convert to bytes in eax + and $0xffff, %eax + shl $10, %eax + + mov $boot_mem_map, %esi + movl $0x100000, (%esi) + mov %eax, 4(%esi) + + movl $1, boot_mem_map_size + clc + ret + +x88_fail: + stc + ret + + + # this part is placed at the very end of all low memory sections + .section .bootend,"ax" + .global boot_mem_map_size +boot_mem_map_size: .long 0 + .global boot_mem_map +boot_mem_map: .space 128 + + .align 4 + .global boot_drive_number +boot_drive_number: + .long 0 # buffer used by the track loader ... to load tracks. .align 16 buffer: + .global low_mem_buffer +low_mem_buffer: