Add N2 OTG-USB guide (#15863)

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>
Co-authored-by: Franck Nijhof <git@frenck.dev>

source/hassio/flashing_n2_otg.markdown

@@ -0,0 +1,57 @@
+---
+title: "Flashing an ODROID-N2+"
+description: "Using Petitboot and OTG-USB to flash the eMMC on your Odroid N2"
+---
+
+Home Assistant can be flashed to an ODROID-N2+ by connecting the device directly to your computer via the USB-OTG connection on the front of the board. The device contains the Petitboot bootloader, which allows the ODROID-N2+ storage to show up as it were a USB drive.
+
+_All these instructions work the same for the ODROID-N2 (non-plus version)._
+
+## What you will need
+
+To flash your eMMC using Petitboot and OTG-USB, you will need the following items:
+
+- HDMI cable and monitor
+- USB keyboard
+- USB 2.0 to micro-USB cable
+
+### Enabling SPI boot mode
+
+Remove the case of your ODROID-N2+
+
+![Photo of the removed case](/images/hassio/screenshots/case-removed.jpg)
+
+Next, locate the toggle for boot mode and switch it from MMC to SPI.
+
+![Photo of the SPI toggle switch](/images/hassio/screenshots/toggle_spi.jpg)
+
+Connect a USB keyboard and HDMI connected monitor to your ODROID-N2+, and then connect power.
+
+### Enabling USB drive mode
+
+The ODROID-N2+ will now boot into a terminal. Select `Exit to shell` from the menu.
+
+![Exit to shell](/images/hassio/screenshots/exit-shell.png)
+
+Use the following command at the console to confirm the storage device node:
+
+```bash
+ls /dev/mmc*
+```
+
+Set the storage device on the ODROID-N2+ as a mass storage device using `ums` (USB Mass storage mode)
+This will configure the ODROID-N2+ and OTG to act as a memory card reader.
+
+```bash
+ums /dev/mmcblk0
+```
+
+### Flashing Home Assistant
+
+Connect the ODROID-N2+ to your PC via the micro-USB port at the front of the ODROID-N2+. When the ODROID-N2 is recognized as a USB connected storage device, you can flash the eMMC with [Etcher](https://www.balena.io/etcher/) using the latest stable version of Home Assistant OS for the [ODROID-N2+](https://github.com/home-assistant/operating-system/releases/latest) (hassos_odroid-n2-XXXX.img.gz).
+
+When the flash process is complete, disconnect the ODROID-N2+ from your PC and remove the power cable. Remove the USB and HDMI cable, and make sure to toggle the boot mode switch back to MMC.
+
+Once it is back in its case, connect your ODROID-N2+ to your network with an Ethernet cable and plug in power.
+
+If your router supports mDNS, you will be able to reach your installation on `http://homeassistant.local:8123`.  If your network doesn’t support mDNS, you’ll have to use the IP address of your ODROID-N2+ instead of `homeassistant.local`. For example, `http://192.168.0.9:8123`. You should be able to find the IP address of your ODROID-N2+ from the admin interface of your router.

source/hassio/installation.markdown

@@ -15,6 +15,7 @@ The following will take you through the steps required to install Home Assistant
      - [Raspberry Pi 4 Model B (1 GB, 2 GB, 4 GB and 8 GB model) 64-bit][pi4-64] (64-bit is required for 8 GB model)
      - [Tinkerboard][tinker]
      - [Odroid-C2][odroid-c2], [Odroid-C4 (Beta)][odroid-c4], [Odroid-N2][odroid-n2], [Odroid-XU4][odroid-xu4]
+       - [Guide: Flashing Odroid-N2 using OTG-USB][otg-usb]
      - [Intel NUC][intel-nuc]
 
    - As a virtual appliance (x86_64/UEFI):
@@ -121,3 +122,4 @@ If you would like to test next release before anyone else, you can install the b
 [ssh]: /addons/ssh/
 [pi-power]: https://www.raspberrypi.org/help/faqs/#powerReqs
 [configure]: /getting-started/configuration/
+[otg-usb]: hassio/flashing_n2_otg/