-# pcboot - bootable PC demo/game kernel
+# 256boss - bootable launcher for 256byte intros
# Copyright (C) 2018 John Tsiombikas <nuclear@member.fsf.org>
#
# This program is free software: you can redistribute it and/or modify
.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
# 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
# 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
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
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
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
-
-# 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
+ .global boot_drive_number
+boot_drive_number:
.long 0
-saved_esp: .long 0
-saved_ebp: .long 0
-
- # 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)
-
- # modify the int instruction do this here before the
- # cs-load jumps, to let them flush the instruction cache
- mov $int_op, %ebx
- movb 8(%ebp), %al
- movb %al, 1(%ebx)
-
- # 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
-
- # load registers from the int86regs struct
- mov %esp, saved_esp
- mov %ebp, saved_ebp
- mov 12(%ebp), %esp
- popal
- popfw
- pop %es
- pop %ds
- # ignore fs and gs for now, don't think I'm going to need them
- mov saved_esp, %esp
-
- # call 16bit interrupt
-int_op: int $0
-
- mov saved_ebp, %ebp
- mov 12(%ebp), %esp
- add $38, %esp
- push %ds
- push %es
- pushfw
- pushal
- mov saved_esp, %esp
-
- # 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
-
- # restore 32bit interrupt descriptor table
- lidt (saved_idtr)
- sti
- popal
- pop %ebp
- ret
-
-
# buffer used by the track loader ... to load tracks.
.align 16
buffer:
projects / bootcensus / blobdiff