backported fixes from 256boss:

[bootcensus] / src / boot / boot2.s

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index 5aeebaa..894c7fa 100644 (file)
--- a/src/boot/boot2.s
+++ b/src/boot/boot2.s
@@ -1,5 +1,5 @@
 # pcboot - bootable PC demo/game kernel
-# Copyright (C) 2018  John Tsiombikas <nuclear@member.fsf.org>
+# Copyright (C) 2018-2019  John Tsiombikas <nuclear@member.fsf.org>
 # 
 # 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
@@ -21,10 +21,17 @@
        .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
 
@@ -42,9 +49,6 @@
        # 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
@@ -227,11 +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 $0xf, %al
        out %al, %dx
+0:
 
        mov $10, %ax
        call putchar
@@ -248,7 +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
@@ -451,15 +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
 
@@ -767,6 +811,8 @@ saved_eax: .long 0
 saved_es: .word 0
 saved_ds: .word 0
 saved_flags: .word 0
+saved_pic1_mask: .byte 0
+saved_pic2_mask: .byte 0
 
        # drop back to unreal mode to call 16bit interrupt
        .global int86
@@ -779,6 +825,16 @@ int86:
        sidt (saved_idtr)
        lidt (rmidt)
 
+       # save PIC masks
+       pushl $0
+       call get_pic_mask
+       add $4, %esp
+       mov %al, saved_pic1_mask
+       pushl $1
+       call get_pic_mask
+       add $4, %esp
+       mov %al, saved_pic2_mask
+
        # modify the int instruction. do this here before the
        # cs-load jumps, to let them flush the instruction cache
        mov $int_op, %ebx
@@ -812,7 +868,6 @@ int86:
        pop %es
        pop %ds
        # ignore fs and gs for now, don't think I'm going to need them
-       mov saved_esp, %esp
 
        # move to the real-mode stack, accessible from ss=0
        # just in case the BIOS call screws up our unreal mode
@@ -829,7 +884,7 @@ int_op:     int $0
        mov %ds, saved_ds
        mov %es, saved_es
        pushfw
-       pop %ax
+       popw %ax
        mov %ax, saved_flags
 
        # re-enable protection
@@ -855,7 +910,11 @@ int_op:    int $0
        pushw %ax
        mov saved_es, %ax
        pushw %ax
-       mov saved_flags, %ax
+       # grab the flags and replace the carry bit from the saved flags
+       pushfw
+       popw %ax
+       and $0xfffe, %ax
+       or saved_flags, %ax
        pushw %ax
        mov saved_eax, %eax
        pushal
@@ -863,12 +922,43 @@ int_op:   int $0
 
        # restore 32bit interrupt descriptor table
        lidt (saved_idtr)
+
+       # restore PIC configuration
+       call init_pic
+
+       # restore IRQ masks
+       movzbl saved_pic1_mask, %eax
+       push %eax
+       pushl $0
+       call set_pic_mask
+       add $8, %esp
+
+       movzbl saved_pic2_mask, %eax
+       push %eax
+       pushl $1
+       call set_pic_mask
+       add $8, %esp
+
+       # keyboard voodoo: with some BIOS implementations, after returning from
+       # int13, there's (I guess) leftover data in the keyboard port and we
+       # can't receive any more keyboard interrupts afterwards. Reading from
+       # the keyboard data port (60h) once, seems to resolve this. And it's
+       # cheap enough, so why not... I give up.
+       push %eax
+       in $0x60, %al
+       pop %eax
+
        sti
        popal
        pop %ebp
        ret
 
 
+       .align 4
+       .global boot_drive_number
+boot_drive_number:
+       .long 0
+
        # buffer used by the track loader ... to load tracks.
        .align 16
 buffer: