OSDev.org

The Place to Start for Operating System Developers
It is currently Wed Oct 28, 2020 9:26 am

All times are UTC - 6 hours




Post new topic Reply to topic  [ 1 post ] 
Author Message
 Post subject: Alter - MBR boot loader with new features
PostPosted: Tue Mar 01, 2011 2:11 am 
Offline
Member
Member

Joined: Fri Nov 16, 2007 1:59 pm
Posts: 612
Alter 3 now in testing.

New features for users:
1. Booting actsec sector when no active boot partition and Alt key (or other control key(s)) is not held down.
2. Booting altsec sector when no alternative boot partition and Alt key (or other control key(s)) is held down.
3. Booting from alternative boot partition when Alt key (or other control key(s)) is held down.

Alter 3 uses ten bytes of MBR for special purposes:

Name/Offset/Size
actsec/432/4
Description
Number of sector which is booted when feature 1 is enabled. To disable feature 1 put zero into this field.

Name/Offset/Size
altsec/436/4
Description
Number of sector which is booted when feature 2 is enabled. To disable feature 2 put zero into this field.

Name/Offset/Size
keyflags/444/1
Description
Set of bits which define the keys for activating extended mode features (8 - any Alt key).

Name/Offset/Size
altpart/445/1
Description
Number of alternative boot partition or zero. Values 1-4 are used for primary partitions. Values 5-255 are reserved for additional partitions.

Supported modes (keyflags/altpart):
0/0 - normal mode (feature 1 is enabled).
0/X - normal mode with pre-storing altpart value.
X/0, 5-255 - extended mode (feature 2 is enabled).
X/1-4 - extended mode (feature 3 is enabled).

New features for developers:
Support for "Secondary Loader Boot Specification Rev.3". This specification describes following interface between MBR boot loader (stage 0) and "primary loader" (stage 1):
  • ds:si - pointer to descriptor (PT entry) of boot partition (if byte at 7DFFh holds 88h).
  • dl - number of boot disk.
  • dh - number of boot partition or zero (if byte at 7DFFh holds 88h).

Download links:
alter-3.bin (432 bytes)
alter-3e.bin (432 bytes) - Alter 3 Extra Edition (one second delay for waiting for key press added).

_________________
If you have seen bad English in my words, tell me what's wrong, please.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1 post ] 

All times are UTC - 6 hours


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group