This guide is probably obsolete, use this instead. Just drag your otp.bin to your browser window and it will compile it for you, I'm leaving the original guide below for those who likes to DIY.

Original post:
Hopefully this guide should silence the whiners

Before we begin I have to say this is my very first guide that I made from my experience and information from other Temp members, and English isn't my primary language so I might make mistakes. If you find any just tell me and I'll try my best to correct them. (The screenshot in the spoiler was taken in OS X with wineskin because I'm lazy, this guide is for Windows only)

So you just dumped your OTP and wondering how do you compile A9LH for your 3DS? Here's a guide to instruct you how to compile and install the payload on your device. This guide assumes you know the basics of 3DS homebrew and Windows command prompt,and just stay away from this if you don't - menuhax is good enough for most people IMO. (I am serious)

DISCLAIMER: Any modifications to your 3DS are done at your own risk. I am not responsible for any bricks that may occur during this process (use your common sense and read the guide carefully)

0. Requirements:

• arm9loaderhax source (https://github.com/capito27/arm9loaderhax), it includes all the file dumps you'll need, except your own OTP
• miniPasta (https://github.com/d0k3/MiniPasta/releases , N3DS only)
• OTP.bin (DO NOT use dumps that are not from your console or the one included with the A9LH source, you WILL brick your 3DS, guaranteed.)
• Python 2.7.11 x86-64 (https://www.python.org/downloads/windows)
• PyCrypto (http://www.voidspace.org.uk/python/pycrypto-2.6.1/pycrypto-2.6.1.win-amd64-py2.7.exe)
• Make(http://gnuwin32.sourceforge.net/packages/make.htm)
• devkitARM (https://sourceforge.net/projects/devkitpro/files/Automated Installer/ , part of devkitPro)
• Your brain

1. Preparation

1. If you have an existing install of Python 3.x/32-bit 2.7.x, remove it first
2. Install Python 2.7 x86-64, make sure you install "add python.exe to patch" sub feature during installation (it's not set by default)
   
   Spoiler

   
3. Install PyCrypto
4. Install devkitPro 1.6.0, you will be be presented with tons of packages but the only ones we're interested are under devkitARM, simply uncheck everything else.
   
   Spoiler

   
5. Install Make, you should download the file with md5:8ae51379d1f3eef8360df4e674f17d6d

2. Compile A9LH

1. Extract the A9LH source to any directory
2. Copy your OTP.bin to the data_input folder and overwrite the one that's included with the zip file
3. Open a CMD window (Shift+right click on the explorer window or cd into it manually)at the root directory of the source files, type "make" (without quotes) and enter.
4. Wait for a minute or so, a data_output folder will appear and there should be no errors
5. Copy the arm9loaderhax.3dsx file from the newly created folder to /3ds/ on your SD card (the installer is built specifically for the 3DS you dumped its OTP from, if you want to install A9LH on more than one 3DS you will to recompile the payload with their respective OTP.bin files)

3.1 Installing A9LH

1. Ensure you have a dump of your SysNAND before you continue
2. Enter hblauncher using an entry point of your choice
3. Run arm9loaderhax.3dsx (see below if you're stuck on "exploiting arm9")
4. The payload will be installed to your NAND and your 3DS will then be rebooted to black screens afterwards. Don't panic, turn off your 3DS

3.2 "exploiting arm9" workaround (required for n3DS, not sure about o3DS)

1. Download and copy the miniPasta 3dsx to your SD card
2. Run miniPasta, the screen will turn black for a few seconds and you will be kicked back to home menu afterwards
3. Re-enter hblauncher and try running the A9LH installer again

4. Testing the payload + conclusion
There's a test binary (forgot who made it) that will power off your 3DS upon pressing any buttons except ZL, ZR or home. Simply copy it to the root of your SD card, wait for a couple seconds and press a button. If your 3DS powers off, then A9LH is successfully installed and woking correctly (congrats). If your 3DS powers off the moment you turn it on, check if the file is named "arm9loaderhax.bin" and placed in the root directory, if it power led stay on and won't respond to button pressed then your 3DS is probably bricked
If you want a cold boot (permanent) CFW (the reason to get A9LH in the first place), check out @Aurora Wright's ReiNand fork. She already documented it very well so I'm not going through it in this thread

FAQ
Q: I'm getting "python: command not found"
A: Make sure you select "add python.exe to path" during installation, alternatively you can set the PATH variable manually by entering this in cmd (Thanks @Kever)

set PATH=C:\Python27;%PATH%

Q: How to uninstall A9LH?[/SIZE][/SIZE]
A: Restore a sysNAND backup made before running arm9loaderhax.3dsx

 

[solsolis]

With this will be possible to run an ds rom on the 3ds without r4?

No. Not right now. Maybe not ever.

 

[Dennis G]

Hey Guys, does anyone know what is the cause of this?

Cmd:
make[1]: Entering directory `/c/Users/Dennis/Desktop/arm9loaderhax-master/payload_stage1'
linking payload_stage1.elf
built ... payload_stage1.bin
make[1]: Leaving directory `/c/Users/Dennis/Desktop/arm9loaderhax-master/payload_stage1'
8+1 records in
8+1 records out
4168 bytes (4.2 kB) copied, 0.003 seconds, 1.4 MB/s
FIRM0 done!
FIRM1 done!
Traceback (most recent call last):
File "common/sector_generator.py", line 1, in <module>
from Crypto.Cipher import AES
File "c:\Python27\lib\site-packages\Crypto\Cipher\AES.py", line 50, in <module>
from Crypto.Cipher import _AES
ImportError: DLL load failed: %1 is not a valid Win32 application.
make: *** [sector] Error 1

thanks if someone can figure this out, probally some small thing that i oversee =P

 

[SomeGamer]

If I have the "old" A9LH installed, how can I update to the newer one which has screen init? (I've already built the new 3dsx installer.)

 

[Madridi]

Followed instructions, and it went well. Thanks

 

[dkabot]

If I have the "old" A9LH installed, how can I update to the newer one which has screen init? (I've already built the new 3dsx installer.)

You can use the 3dsx installer if you really want, use the dark-samus repo if you do.
If you go to A9LH discussion thread, they posted an updater that you run from A9LH itself without recompiling.
I'd recommend that, but whatever you feel like trying.

 

[SomeGamer]

You can use the 3dsx installer if you really want, use the dark-samus repo if you do.
If you go to A9LH discussion thread, they posted an updater that you run from A9LH itself without recompiling.
I'd recommend that, but whatever you feel like trying.

Could you link me to the updater? (I'm going back pages on that thread as we speak.)

 

[dkabot]

Could you link me to the updater? (I'm going back pages on that thread as we speak.)

https://gbatemp.net/threads/arm9loader-technical-details-and-discussion.408537/page-116#post-6112713
Put both files on SD, rename installer.bin to arm9loaderhax.bin and try it.
No bricks from it at all thus far, though some cases where it doesn't work right on some N3DS'; be sure to report it if that happens

 

[SomeGamer]

https://gbatemp.net/threads/arm9loader-technical-details-and-discussion.408537/page-116#post-6112713
Put both files on SD, rename installer.bin to arm9loaderhax.bin and try it.
No bricks from it at all thus far, though some cases where it doesn't work right on some N3DS'; be sure to report it if that happens

It worked on my O3DS! What do you mean by

some cases where it doesn't work right on some N3DS

?

 

[dkabot]

It worked on my O3DS! What do you mean by

?

There are two bugs on N3DS thus far, not found originally because test hardware was O3DS.
One, the installer doesn't init screen. Can still install.
The other, installer doesn't work at all. Can still compile 3dsx from repo and do that.

As you have O3DS and it worked, not necessary to worry about =P

 

[SomeGamer]

There are two bugs on N3DS thus far, not found originally because test hardware was O3DS.
One, the installer doesn't init screen. Can still install.
The other, installer doesn't work at all. Can still compile 3dsx from repo and do that.

As you have O3DS and it worked, not necessary to worry about =P

I also have a N3DS!

--------------------- MERGED ---------------------------

The only thing I want to know for sure is even if it doesn't work, it doesn't brick, right?

 

[dkabot]

I also have a N3DS!

Ah. Then, there you go.
As this is the "how to compile" thread, I think we're done here. Good luck if you try it on the N3DS.

Thus far, nothing has happened. If it does, I'm sure it'll appear in relevant threads.

 

[SomeGamer]

Ah. Then, there you go.
As this is the "how to compile" thread, I think we're done here. Good luck if you try it on the N3DS.

Thus far, nothing has happened. If it does, I'm sure it'll appear in relevant threads.

Installed flawlessly on my N3DS too! Thanks for your help!

 

[Daidouji]

Just to state my case also. @SomeGamer told me via PM how to use this update.

I had the "first bug" @dkabot said.... the screenInit on NEW 3DS happened to me BUT I just pressed "A" and the screen lit and showed me it installed the update... The screen showed text and "lit" as far as I had the "A" Button pressed.
I then proceeded to restore my previous a9hl.bin and it works now! my custom reiNAND Splash is shown every single time I turn on the console! This is so awesome! Thanks a lot guys =D

 

[Patxinco]

Everything worked perfect!!
Aureinand working on my O3DSXL.
Now some tips if someone wants it:

If pycripto says that doesn't find the python install, you're not using the right version of it, either 32bits or the 64Bits.
If when trying to compile (cmd "make") you get ONLY errors everywhere, edit the makefile file, and change "Python=python" to "Python=C:/Python27/python.exe"
And if, besides that, you get error somewhere, make sure the route of the folder where the makefile file is, HAS NOT a space anywhere!!!

Thanks to @lefthandsword , @Conn0r and @solsolis !!!

 

[Koryushin]

If when trying to compile (cmd "make") you get ONLY errors everywhere, edit the makefile file, and change "Python=python" to "Python=C:/Python27/python.exe"

A better solution is to add C:/Python27/ to the environment path.

 

[Patxinco]

A better solution is to add C:/Python27/ to the environment path.

I found the other way faster and more permanent, since i don't have to type it everytime i want to compile, also, i'd recommend doing 2 or 3 compilations and checking md5 of them, to see if something went wrong.

 

[Koryushin]

By adding it to your path it's permanent.
And the same thing shall be done to Devkitpro/dekitarm.

 

[Dennis G]

I install python when installing pycrypto it says "Can't find Python 27"

You have to uninstall python 2.7 reinstall and then on the first screen select "Only for current user" if you installed it the first time you automaticly install it for all users and that makes crypto not able to find it. that will fix it

 

[D34DL1N3R]

Should I uninstall menuhax before or after installing arm9loaderhax? Or just leave menuhax installed?

 

[Daidouji]

Should I uninstall menuhax before or after installing arm9loaderhax? Or just leave menuhax installed?

I just installed it... I guess you can uninstall it first, then install A9LH