3DS:Ntrboot

ntrboot is a hardware exploit for the 3DS that relies on a DS flashcart with a version of boot9strap flashed to it to boot a  payload named  from its attached SD. It is compatible with all console types & system versions and has very few requirements besides the flashcart, making it the best (and occasionally, only) option for cases where multiple parts of your system such as shoulder buttons, DSiWare Management, or DS mode are broken or you need to recover from a brick.

Requirements
To use ntrboot, you need a DS flashcart compatible with the ntrboot exploit (see a full list of such carts here), a small magnet for all models except the old 2DS, working, , and buttons, and a working cartridge reader. If you have not already flashed ntrboot to the flashcart, you will need also one of three things to do so: If you do not have one of these, you must either use a pre-flashed cart such as the R4i-SDHC B9S or install CFW with another method first.
 * 1) A DSi or 3DS with a system version within the flashcart's supported range
 * 2) A DS/DS Lite
 * 3) A second 3DS with boot9strap already installed

How it works
If your console is in sleep mode while the buttons are accessible (either via a magnet or the old 2DS' sleep switch) and you hold the keycombo, , and , then press while continuing to hold the other three buttons, the console attempts to directly boot from an inserted DS cartridge. This only works when the flashcart's firmware can be used as a bootloader, and was likely intended for Nintendo-made recovery cartridges. But since a flashcart capable of ntrboot runs boot9strap, it boots, it looks for a file on the flashcart's SD root named, and immediately loads into it. This can be used with any  payload with the correct name, which is also how boot9strap is installed to a console via our guide.

Usage
The most commonly useful applications of ntrboot are listed here.

Flashcart compatibility
Not all flashcarts are compatible with the ntrboot exploit due to differences in their chipsets. The three main issues are a lack of documented flashing commands for the cart, the cart being accidentally made unable to flash safely with ntrboot, or the cart using encryption to make unverified firmware result in a brick. Understandably, it can be hard to figure out if a cart doesn't have any of these issues due to clones, counterfeits, and custom-made flashcarts all existing, which is why our guide provides a list of known compatible flashcarts.

Issues ntrboot cannot solve
ntrboot is not capable of fixing hardware issues or a locked NAND - however, a locked NAND specifically has only been known to occur with Gateway-3DS flashcarts & [3Dsafe] (neither of which should be used anymore), and can be fixed with a hardmod and NAND backup like one linked to on a page on our guide.

Normal flashcart usage with ntrboot installed
Almost all flashcarts lose the ability to load  files when ntrboot is installed, for one of two reasons: As a result, you must choose between running .nds files or running ntrboot, unless using an Acekard 2i or a flashcart with a 'switch' to change between ntrboot and NDS modes. Note that an Acekard 2i still loses  access on an unmodded DSi/3DS when ntrboot is installed due to Nintendo blocking its firmware. To restore regular functionality, reflash the flashcart's original firmware.
 * Flashing ntrboot overwrites the flashcart's ability to run  files. This applies to most carts.
 * The flashcart stops spoofing a retail cartridge's information, and the original firmware for the cart is blocked by Nintendo (only some carts made prior to 2013 are blocked) - this only applies in practice to the Acekard 2i.

Dev consoles
The normal guide for ntrboot does not work on developer consoles, and a specialized guide is required to install CFW for them - a working guide existed at [panda.hacks.guide], but has since been closed off due to a lack of people capable of maintaining it.