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[mbr] finalize protective message MBR

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* Note that msg.txt uses codepage 850
This commit is contained in:
Pete Batard 2020-02-19 18:48:24 +00:00
parent bfbb9d2ed5
commit 98c630d81a
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GPG key ID: 38E0CF5E69EDD671
4 changed files with 64 additions and 22 deletions
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48
res/mbr/msg.S
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@ -1,6 +1,6 @@
/********************************************************************************/
/********************************************************************************/
/* MSG - A protective MBR that displays an ASCII message located in the */
/* following sectors. */
/* subsequent sectors. */
/* */
/* Copyright (c) 2019-2020 Pete Batard <pete@akeo.ie> */
/* */
@ -139,20 +139,50 @@ display_msg: # Display the message
mov ax, es
mov ds, ax
call print_msg
jmp halt_system
jmp prompt_user
display_err: # Read error -> display shorter message from this MBR
mov si, offset err_msg
call print_msg
halt_system: # Halt the system
hlt
jmp halt_system # Just in case...
prompt_user:
xor ax, ax
mov ds, ax
mov si, offset prompt_string
call print_msg # Prompt the user
call flush_keyboard
wait_for_keyboard:
mov ah, 0x01
int 0x16 # KEYBOARD - CHECK BUFFER, DO NOT CLEAR
jnz reboot # Z is clear when characters are present in the buffer
mov ah, 0x02
int 0x16 # KEYBOARD - GET SHIFT STATUS
and al, 0x04 # AL = shift status bits
jz wait_for_keyboard
reboot: # Trigger a reboot
xor ax, ax
mov ds, ax
mov ax, 0x1234
mov [0x473], ax
jmp 0xffff:0000
/********************************************************************************/
/* Subroutines */
/********************************************************************************/
flush_keyboard: # Flush the keyboard buffer
mov ah, 0x01
int 0x16 # KEYBOARD - CHECK BUFFER, DO NOT CLEAR
jz 0f # Z is set if no character in buffer
mov ah, 0x00
int 0x16 # KEYBOARD - READ CHAR FROM BUFFER
loop flush_keyboard
0: ret
# ---------------------------------------------------------------------------
print_msg: # Print NUL terminated string in DS:SI to console
lodsb
cmp al, 0x00 # NUL?
@ -204,7 +234,9 @@ print_msg: # Print NUL terminated string in DS:SI to console
/* Data section */
/********************************************************************************/
err_msg:
.string "*** ERROR: THIS MEDIA CANNOT BOOT IN LEGACY MODE ***"
.string "\r\n \\04*** ERROR: THIS MEDIA CANNOT BOOT IN LEGACY MODE ***\\07\r\n"
prompt_string:
.string "\r\n\r\n \\70Please remove this media and press any key to reboot\\07"
/********************************************************************************/
/* From offset 0x1b8, the MBR contains the partition table and signature data */