Reboot the computer using assembly language

[Kirdow]

I want to reboot the computer. I know how to shutdown the computer by connecting to ASM and the shutting down. but now I want to be able to reboot.
I've done some general researched and saw that reboots is done by first shutting down and also sending a "message" to the motherboard that right before you power off, you cancel, reset some values, and instead act if you just pressed the button and powered on the computer.

Remember, If it's possible, I don't want to implement some complicated library and so on. I would want pure assembly and from scratch (if possible). And what I want is when I reboot, I want BIOS to go through the boot order, so if the user has my OS to boot after for example Windows, which means he has to go into bios manually and then start my OS manually, then when my OS performs a reboot, BIOS should go though the boot order and see "aah, I should boot Windows". Get it? So I don't just want to reload my bootloader from scratch. I want the whole system to reboot, kind of the reboot button on Windows XP/7/8/8.1/10 etc... So how do I add a reboot functionality to my code? Please show code to help me understand what to do

[Nable]

In fact, reboot is much simpler than shutdown. You can find general examples here: http://wiki.osdev.org/Reboot .
But you should be careful: all power-related things are highly system-specific (some method could work on your PC and lead to a total mess on another one). Proper ACPI implementation (I'm in doubt whether you have it) covers a high percentage but it's far from 100%, as there are tons of machines with broken ACPI (or even complete absence of it).

tl;dr: one method isn't enough, you should implement many of them and apply them in a right order.

[micccy]

Remember that you can also do a CPU reset via the 8042 keyboard controller.
If you are working in (un)real mode, you can perform a very simple reboot jumping to the POST procedure (FFFF:0000):

Code: Select all

PUSH    0FFFFh
PUSH    0000h
RETF

That puts the address of the POST procedure into the stack and then perfmorms a RETF which read the value to put in CS:IP from the stack.

Sorry if my english isn't very good

[Nable]

Remember that you can also do a CPU reset via the 8042 keyboard controller.

But one should also note that 8042 (and sometimes even its emulation) is absent on recent systems. Attempt to use I/O ports of absent device could lead to unexpected results.

[BrightLight]

But one should also note that 8042 (and sometimes even its emulation) is absent on recent systems. Attempt to use I/O ports of absent device could lead to unexpected results.

That's why 8042 should be a fallback method, and ACPI reset should be the main method.

[sebihepp]

Why not just generate a "triple fault"?

[Octocontrabass]

A triple fault should be the last resort, since it won't reboot some PCs.

[Kirdow]

I know this one is a few weeks old but I think I need to open this one again.
I had this to reboot:

Code: Select all

db 0x0ea
dw 0x0000
dw 0xFFFF

but I've seen on multiple places this is not a good idea and could sometimes fail, like it did for me now after fixing segments.

So how do I reboot using something like APM? and also, I am in 16-bit Real Mode, and if you do CTRL+ALT+DEL it reboots the system. so I wonder, is there a way to manually do that from code?
I would like to have both ways.

[BASICFreak]

I know this one is a few weeks old but I think I need to open this one again.
I had this to reboot:

Code: Select all

db 0x0ea
dw 0x0000
dw 0xFFFF

but I've seen on multiple places this is not a good idea and could sometimes fail, like it did for me now after fixing segments.

So how do I reboot using something like APM? and also, I am in 16-bit Real Mode, and if you do CTRL+ALT+DEL it reboots the system. so I wonder, is there a way to manually do that from code?
I would like to have both ways.

If you are in real mode, why not look at int 19h (BootStrap Loader) http://www.ctyme.com/intr/rb-2270.htm

[Kirdow]

I know this one is a few weeks old but I think I need to open this one again.
I had this to reboot:

Code: Select all

db 0x0ea
dw 0x0000
dw 0xFFFF

but I've seen on multiple places this is not a good idea and could sometimes fail, like it did for me now after fixing segments.

So how do I reboot using something like APM? and also, I am in 16-bit Real Mode, and if you do CTRL+ALT+DEL it reboots the system. so I wonder, is there a way to manually do that from code?
I would like to have both ways.

If you are in real mode, why not look at int 19h (BootStrap Loader) http://www.ctyme.com/intr/rb-2270.htm

I don't have time to test it right now, but does this reboot thing go through the boot disk order or does it just reboot the floppy? for example when I develop, I have the harddrive to boot before the floppy, so when I use int 19h, will it in this case boot from the harddrive or the floppy?

[BASICFreak]

I know this one is a few weeks old but I think I need to open this one again.
I had this to reboot:

Code: Select all

db 0x0ea
dw 0x0000
dw 0xFFFF

but I've seen on multiple places this is not a good idea and could sometimes fail, like it did for me now after fixing segments.

So how do I reboot using something like APM? and also, I am in 16-bit Real Mode, and if you do CTRL+ALT+DEL it reboots the system. so I wonder, is there a way to manually do that from code?
I would like to have both ways.

If you are in real mode, why not look at int 19h (BootStrap Loader) http://www.ctyme.com/intr/rb-2270.htm

I don't have time to test it right now, but does this reboot thing go through the boot disk order or does it just reboot the floppy? for example when I develop, I have the harddrive to boot before the floppy, so when I use int 19h, will it in this case boot from the harddrive or the floppy?

From the link I gave:

(Table 00653)
Values Bootstrap loader is called with (IBM BIOS):.
CS:IP = 0000h:7C00h.
DH = access

bits 7-6,4-0:
Don't care

bit 5:
=0 device supported by INT 13.
DL = boot drive
00h first floppy
80h first hard disk

So, as with reading a disk DL = drive.