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SPC Player

SNES music player in your browser with original hardware and Arduino.

arduino-spc

Table of Contents

What is this?

Video in action here.

With this project you are able to play original SNES SPC audio files from your browser with original hardware. All you need is Arduino Micro and original SNES Audio Processing Unit (APU). Deployed browser player can be found here. Playing songs also works from Python command-line tool. If you are interested how this project works check sections How it Works? and Resources.

For playing you also need to download your favorite SNES SPC music tracks. These can be downloaded from Zophar's website. Search for a game and download original music files. Files will end with .spc ending. I've included one Donkey Kong Country 2 song in root of the project that you can use for quick testing.

Project is develop on Linux machine and not tested on other platforms. Although it should work because of multiplatform tools used. If you stumble upon bugs, please file an issue here in GitHub.

This project was also featured in hackaday.

Structure of the Project

Project consist of two music track uploading frontend tools (browser and Python) and Arduino code for communicating with APU and with your computer. Browser based frontend code lives under frontend-web folder and Python code under frontend-python folder. Arduino code lives under backend folder.

Project also contains InkScape SVG image files under images folder and KiCad schemas under schemas folder.

How to Use

Connecting APU to Arduino

First you need to connect APU to Arduino. Here is APU pinout looking from the top side of the unit:

api-pinout

Signal and symbol explanations:

  • ~ means an active low signal.
  • PA7 is port address bit 7, connected to active low chip select (~CS) pin on the SPC700 chip. Pull this low to GND to enable the chip.
  • PA6 is port address bit 6, connected to chip select (CS) pin on the SPC700 chip. Pull this high to 5V to enable the chip.
  • PA0 and PA1 are port address bits 0 and 1. Used to select which port from 0 to 3 to write or read.
  • From D0 to D7 are bidirectional data lines for input and output a single byte.
  • RD is active low read, APU will write data to lines D0 to D7 when pulled low.
  • WR is active low write, APU will read data from lines D0 to D7 when pulled low.
  • RESET is active low reset line. When held low SPC is in reset mode.
  • SMPCK is a clock output from DSP with average clock rate of 2.23 MHz.
  • MUTE is active low mute output from DSP, it's 0V when DSP is muted and 5V when not.

Here is how you need to connect APU to Arduino:

scema

Uploading Arduino Code

Arduino based backend code uses PlatformIO CLI tool for managing the project and its dependencies instead of Arduino IDE. So to compile and upload the code you need to download PlatformIO and build the project using it. First download and install it from aforementioned website. Installing either IDE or CLI is fine. Generally I prefer CLI over IDE, so the following instructions are written with CLI.

After installing PlatformIO go to backend folder. If you are using browser frontend, you can simply run:

pio run

This will download needed tool and libraries. Compile the code and upload it to the board. Also you should see popup window from Chrome pointing to deployed browser player. If not, then it can be found here.

By default code uses WebUSB serial to communicate with the browser. Both WebUSB and normal serial cannot be used at the same time. If you are using Python frontend or normal serial, then you need to use following command instead and read the section Python Frontend.

pio run --environment serial

Python Frontend

Python frontend can only upload one song at the time. If you want more player like experience with automatically playing the next song. Have a look at browser based frontend instead. Python frontend lives under frontend-python folder. Go to that folder and run following commands inside it.

Project uses version 3.x of Python and uses pySerial library to talk to Arduino over USB serial line. First install pySerial with pip by running following command. Remember to use pip3 and python3 commands if you are using Debian based system like Ubuntu.

pip install pyserial

To upload the song with Python you need to know your serial port to which Arduino is connected to. In Linux it will be something similar like /dev/ttyACM0 and on Windows COM4. To list available serial ports run:

python main.py -l

Copy the serial port and replace the following command <serial-port> with it. Now upload the song with:

python main.py <serial-port> ../dkc2-stickerbrush-symphony.spc

If everything is working correctly Python should print following and song will start playing.

opened port /dev/ttyACM0
write CPU registers successful
write DSP registers successful
write first page RAM successful
write second page RAM successful
100%
write rest of the RAM successful
SPC execution started successfully, uploading took 9.22s

Enjoy some awesome SNES music! If you have some problems. Make sure APU is connected to Arduino correctly. For this check Debugging APU Connections.

Browser Frontend

Browser based code uses WebUSB for communicating with Arduino. So check your browser compatibility for it here. For example Chrome and supports it but Firefox does not at time of writing. Deployed player can be found here.

Browser player can play multiple songs more like a real player compared to the Python frontend which only can play one song at the time. Browser frontend lives under frontend-web folder. Go to that folder and run following commands under it.

Application is developed with React and packages are managed with Yarn. So install yarn first for your system from here. After installing install all required packages with:

yarn install

After installing run the application with

yarn start

and go to localhost:3000 with your browser.

With the player you first need to give permission to your use your USB devices and select the correct one to connect to. After connecting successfully you are presented with the player. Player contains some buttons to debug your setup and then button to upload SPC files. Multiple files can be uploaded at the same time. One DKC2 track is include in the project root for testing purposes. When you've uploaded some songs, then just click on any table line to start uploading the song and it should start playing. After the song ends the next song will be played automatically. UI could be better but that is the task for the future...

Enjoy some awesome SNES music! If you have some problems. Make sure APU is connected to Arduino correctly. For this check section below.

Debugging APU Connections

You can test that APU is connected to Arduino correctly. You need to use normal serial line, not WebUSB serial. After uploading the code go to backend folder and run:

pio run --target monitor

This will open serial monitor. Press R to send R character. Arduino should respond with 1 if it's able to reset the APU successfully and 0 when it fails. In that case check your connections and try again.

How it Works?

APU itself is a standalone CPU with it's own RAM and DSP for producing sound. Usually referred as SCP700 CPU (wiki). Then SPC music file is a snapshot of the state of that system just before the song starts to play. The snapshot includes details like values of all CPU and DSP register and whole RAM content.

When SPC700 boots up it will run it's Initial Program Loader (IPL) code. This code is responsible for communicating over parallel lines with SNES main CPU and transferring bytes to SCP700 RAM. It's also responsible of starting execution of uploaded code. In other words meaning when song should start playing.

In this project's case Arduino is talking with IPL program instead of SNES main CPU. Frontend program on PC (Python or browser) is reading SPC700 RAM bytes from SPC file, transferring them to Arduino over USB serial and Arduino then transferring them with IPL program to SPC700 CPU RAM over it's parallel lines. That's in a nutshell how the whole process works. After all RAM bytes and register values have been transferred. Arduino will inject small custom bootcode to SPC700 RAM and tell IPL to start execution from there. The bootcode is responsible for restoring last register and timer values and then jump to actual song program execution. Bootcode can be found from this file backend/src/SpcPlayer.cpp. Bootcode is filled up with details when whole RAM transferring is in progress. After the song starts playing the parallel line communication is dependant on the song and game. Only way to stop the song at this point is just to reset whole APU itself with the reset line.

One interesting detail which change from game to game. When program is running and music is playing. Program is still reading for values from parallel lines. If something is written there from SNES CPU side, then some sound effects are played. For example in Super Mario World Mario's jumping sound is played while the song is playing.

Using Other Arduino Boads

You can also port this code to work on other Arduino boards. Keep in mind that WebUSB serial cannot be used with all boards. For WebUSB serial support check this.

For porting the code to different Arduino board. Take a look at file backend/src/SpcHal.cpp. Which is Hardware Abstraction Layer (HAL) for the platform. Here you can find the low level data communication functions. Functions are directly using pin IO registers for speed purposes. But the equivalent Arduino code is also there commented out which uses digitalRead and digitalWrite functions. Which is much easier to understand. Note that using digitalRead and digitalWrite functions the song upload will be a lot slower!

Resources

Here are the most important resources what I've collected over time when studying for this project. I put them here in hope that someone else working on the same issues find them useful and don't have to waste time finding them.

Most important source of information being original SNES development manual part 1 which can be downloaded from this link: http://folk.uio.no/sigurdkn/snes/snes_manual1.pdf. SNES development manual most important pages include:

  • 153-179 for general sound system and DSP,
  • 180-188 for SPC700 CPU and
  • 237-240 for IPL ROM boot code procedure.

Development manual can be quite hard to read for the first time so that's why it's recommended to read following resources alongside with the manual to put beef around the bones:

Also when I studied for this project I used following project source code for studying purposes https://www.caitsith2.com/snes/apu.htm. Which can also be found from GitHub: https://github.com/emukidid/SNES_APU_SD.

Future Work

Can play all songs that I've tested but most likely not all SPC files work. At the moment only supports SPC file format v0.30. In future more formats could be supported.

If you stumble upon anything please file an issue about it. PRs are also welcome, thanks!

Deploying GitHub Pages

Under frontend-web run:

yarn build
yarn deploy