Boot to custom recovery

1. Install tools

   sudo apt install adb fastboot
   

2. Download the latest TWRP recovery image

   https://dl.twrp.me/fugu/

3. Reboot into the bootloader

   adb reboot bootloader
   

4. Boot the custom recovery image

   sudo fastboot boot twrp-X.X.X-X-fugu.img
   

Set up Amazon Fire TV remote

The remote included with the Nexus Player disconnects a lot (as indicated by the flashing light). The basic Amazon Fire TV remote (not the one with the microphone) seems to work much better.

It mostly works out of the box but benefits from a button remapping, which can be done by following the steps here:

https://forum.xda-developers.com/t/will-the-fire-tv-remote-work-with-the-nexus-player.2939508/page-2#post-63171780

Install RetroArch

1. Install RetroArch from the Google Play Store

   You can install it from the Nexus Player, but if you wish to install it from another device:

   1. Go here:

      https://play.google.com/store/apps/details?id=com.retroarch

   2. Install > Choose a device > Nexus Player > Install

2. Configure the Nexus Player gamepad

   1. With the Nexus remote:

      1. Open RetroArch

      2. Settings tab (press right/left until it says Settings at the top) > Input

         1. User 1 Binds
            1. User 1 Bind All
               1. Bind the keys using the gamepad
               2. For the letter buttons, go by the direction instead of the letter. For example, for User 1 B button (down), press the bottom button on the gamepad (A) instead of the button labeled B on the gamepad
            2. User 1 Save Autoconfig

      3. Quit RetroArch

   2. With the Nexus Player gamepad:

      1. Open RetroArch

      2. Settings tab > Input

         1. Input Hotkey Binds > Menu toggle > press the back button on the gamepad (This allows you to press the back button on the gamepad to open the RetroArch menu while you’re playing a game)

   3. Now when you want to play games with RetroArch, open RetroArch using the Nexus Player gamepad. If you use the Nexus Player remote at any point while RetroArch is running, it will disable the gamepad for some reason.

3. Disable the controller overlay

   1. Settings tab _> _Onscreen Overlay > Display Overlay > Off

4. Install cores

   1. Online Updater > Core Updater
   2. Install whichever cores you like. Some recommended cores:
      • Nestopia (NES)
      • Snes9x (SNES)
      • Mupen64Plus (Nintendo 64)
      • Genesis Plus GX (Genesis)

5. Put the ROMs in place

   1. Using ES File Explorer, create a folder to put the ROMs (e.g. /sdcard/Games/NES)

   2. Copy the ROMs using ES File Explorer (see instructions above for copying files)

6. Add the ROMs to RetroArch

   1. Add Content > Scan Directory > pick any option and browse to the folder where you put the ROMs

   2. Settings tab > Playlists > set each playlist to the correct core (so you don’t have to choose the first time you launch each game)

7. To load a game

   1. Playlists tab > choose a device > choose a game

   2. If you added a ROM but it’s not showing up in the playlist after scanning:

      1. On your PC, do a checksum on the ROM

         crc32 somerom.nes
         

      2. Find the database for your device here:

         https://github.com/libretro/libretro-database

      3. Use the search feature at the top of the page to find the game and its checksum

      4. Make sure the checksum matches. If it doesn’t, download a different version of the ROM

8. Remap A and B buttons for NES

   1. Start an NES game and then press the back button to go back to the RetroArch menu

   2. Go down to Controls

   3. B button > A

   4. Y button > B

   5. A button > Turbo A or —

   6. X button > Turbo B or —

   7. Save Core Remap File

Copy files to the Nexus Player

http://cord-cutters.wonderhowto.com/how-to/sideload-apps-nexus-player-0160364/