Cdi

NESCD-001

An unofficial homemade CD add-on for the NES, just because!

This repo contains the schematics, PCB, 3D printable STLs for the shell, sticker labels, and the firmware.

How it works

It's basically an RP2350B hooked up to both an Everdrive N8 Pro and an IDE CD drive. It reads the game ROM off the CD, uploads it to the Everdrive over USB and asks the menu to install it, then watches a mailbox byte in the cart's CHR RAM for the game to ask for music. The RP2350B is the coordinator in the middle that bridges the NES/Everdrive and the CD drive.

Project video: https://www.youtube.com/watch?v=6D8RWVwW4ZI

Hardware

• The main PCB (see pcb/)
• A standard 40-pin IDE CD drive
• Everdrive N8 Pro

Build

cd firmware && ./flash.sh

Making a disc

The demo game needs cc65 (ca65/ld65), plus python3 with numpy, ffmpeg for the audio, and xorriso to burn.

cd game && make         # demo.nes, four music tracks, and build/demo.img
cd game && make burn    # burn build/demo.img and read it back to check

To put your own game on a disc, pass mkgamedisc.py an iNES ROM and one track per music byte:

python3 firmware/tools/mktrack.py theme.wav -o theme.rom --loop-start 4.2
python3 firmware/tools/mkgamedisc.py -o mygame.img --title "MY GAME" --nes mygame.nes --track 1=theme.rom --verify
firmware/burn.sh mygame.img

Using it

If everything goes right, you should be able to just put a burned disc into the CD drive while the NES is on and sitting on the Everdrive menu. It'll auto-boot the game once it's read and uploaded to the Everdrive.

Playing an audio CD

Arguably the most practical use for this thing: A CD player!

Insert the CD while on the Everdrive menu and it should automatically launch the player.

FAQ

What?

Great question! I came up with the idea for this project while reading about the canceled SNES CD-ROM add-on. I was originally going to make my own version of that add-on, but decided it'd be funnier and weirder if I took it a step further and made one for NES.

Why?

Because it's fun.

Who?

It's me! Your old pal - Throaty Mumbo!

Where are the FMVs you showed in the video?

I chose not to include any FMV-related code here because to get that working I had to semi-reverse engineer Something Nerdy's Bad Apple!! Ultimate NES Demake, which is currently closed source. The team has mentioned they're planning to formally open source their MXM mapper (which this demo presumably uses, actually not sure) once their game Former Dawn is released. I didn't feel good about publishing reverse engineered code from an indie development team for my stupid meme project, especially when they have plans to release it themselves.

Why not stream audio from the Everdrive?

I originally wanted to do this, but was hitting a ceiling on the Everdrive USB bandwidth. I'd likely have to add some form of aggressive compression to make room. It's also a nice touch to use the expansion port instead.

The USB cable poking out on the front is by far the biggest blemish on the design of this contraption, so I did look at moving everything to the expansion port. Unfortunately the bandwidth there is even more limited than the USB route.

Plus, the expansion port audio allows more flexibility with mixing and volume control - hence the volume knob on the front.

How is this thing powered?

A single molex cable from a wall adapter (this one in particular). The 5V/12V rails are split between the CD drive and the board + the NES output. I took the end of a spare NES power cable and hooked it up to a buck converter that converts the 12V input to ~9.5V so you can power the NES as well (the plug pokes out of the top of the box). That way you only need one wall outlet to get the entire thing running. You can also power the NES separately from its regular adapter - the plug coming out of the NESCD is optional.

Couldn't you power everything off VRAW?

This was my initial plan, but it seemed tight considering the stock NES adapter (1.3A) has to power the NES, Everdrive, RP2350, DAC, and the CD drive. The power adapter for that Fideco drive sled I tested with initially outputs at 2A, so I figured a dedicated 2A molex adapter (which supposedly outputs 2A on 5V and 12V each, at least according to the label) would be the minimum. But honestly I didn't actually test running the CD drive and everything else off VRAW at the same time, so this was more of a cautious choice than based off of objective measurement. If it works it'd be a nice improvement for an eventual v2 design.

How do you get back to the Everdrive menu once you've inserted a disc?

This is still something I'm trying to figure out. AFAIK there's no way to trigger a soft reset on the NES. However one guaranteed solution is to hook up the NES power output rail to a relay switch. That way if the board ever needs the NES to reset, it can just turn it on and off from the source. Not super elegant but it should work.