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[mbr] use 80x25:16 text mode rather than 640x480:16 VGA mode

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* This should produce the same output while improving compatibility with systems that have a broken VGA implementation.
* Also fix an LD error with newer gcc toolchains.
This commit is contained in:
Pete Batard 2022-07-04 15:08:55 +01:00
parent 3cf41abf2e
commit 8fb602b8ee
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GPG key ID: 38E0CF5E69EDD671
5 changed files with 20 additions and 26 deletions
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17
res/mbr/msg.S
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@ -2,7 +2,7 @@
/* MSG - A protective MBR that displays an ASCII message located in the */
/* subsequent sectors. */
/* */
/* Copyright (c) 2019-2020 Pete Batard <pete@akeo.ie> */
/* Copyright (c) 2019-2022 Pete Batard <pete@akeo.ie> */
/* */
/* 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 */
@ -31,7 +31,7 @@
/********************************************************************************/
MBR_ADDR = 0x7c00
MBR_RESERVED = 0x1b8 # Start of the reserved section (partition table, etc.)
MSG_SECTOR = 0x22 # First sector of the message (must be after the GPT)
MSG_SECTOR = 0x22 # First sector of the message (must be after the GPT)
NB_SECTORS = 0x08 # Number of sectors to read
PT_MAX = 0x04 # Number of partition entries in the partition table
PT_ENTRY_SIZE = 0x10 # Size of a partition entry in the partition table
@ -85,21 +85,16 @@ mbr:
mov es, ax # Keep allocated RAM segment in ES
clear_display:
mov bh, 0x07
mov ax, 0x007f
int 0x10 # Set Video Mode to 640x480 16 color graphics (VGA)
xor bx, bx
xor cx, cx
mov dx, 0x184f
mov ax, 0x0600
int 0x10 # Clear screen
xor dx, dx
mov ax, 0x0003
int 0x10 # Set Text Mode to 80x25, 16 color (setting mode also clears the screen)
mov ah, 0x02
int 0x10 # Set cursor pos to top left
read_sectors: # Copy the next sectors into RAM
mov ah, 0x41
mov bx, 0x55aa
xor cx, cx
xor dx, dx
int 0x13
jb no_ext # failure to get ext
cmp bx, 0xaa55