RP2040 Doom

This is a port of Doom for RP2040 devices, derived from Chocolate Doom.

Significant changes have been made to support running on the RP2040 device, but particularly to support running the entire shareware DOOM1.WAD which is 4M big on a Raspberry Pi Pico with only 2M flash!

You can read many details on this port in the blog post here.

Note that a hopefully-fully-functional chocolate-doom executable is buildable from this RP2040 code base as a means of verification that everything still works, but whilst they can still be built, Hexen, Strife and Heretic are almost certainly broken, so are not built by default.

This chocolate-doom commit that the code is branched off can be found in the upstream branch.

The original Chocolate Doom README is here.

Code State

Thus far, the focus has been entirely on getting RP2040 Doom running. Not a lot of time has been spent cleaning the code up. There are a bunch of defunct #ifdefs and other code that was useful at some point, but no longer are, and indeed changing them may result in non-functional code. This is particularly true of the whd_gen tool used to convert/compress WADs who's code is likely completely incomprehensible!

Artifacts

You can find a RP2040 Doom UF2s based on the standard VGA/I2S pins in the releases of this repository. There are also versions with the shareware DOOM1.WAD already embedded.

Note you can always use picotool info -a <UF2 file> to see the pins used by a particular build.

Goals

The main goals for this port were:

1. Everything should match the original game experience, i.e. all the graphics at classic 320x200 resolution, stereo sound, OPL2 music, save/load, demo playback, cheats, network multiplayer... basically it should feel like the original game.
2. DOOM1.WAD should run on a Raspberry Pi Pico. There was also to be no sneaky discarding of splash screens, altering of levels, down-sampling of textures or whatever. RP2040 boards with 8M should be able to play at least the full Ultimate Doom and DOOM II WADs.
3. The RP2040 should output directly to VGA (16 color pins for RGB565 along with HSync/VSync) along with stereo sound.

Results

Features:

• Full DOOM1.WAD playable on Raspberry Pi Pico with 2M flash.
• Ultimate Doom and Doom II are playable on 8M devices.
• 320x200x60 VGA output (really 1280x1024x60).
• 9 Channel OPL2 Sound at 49716Hz.
• 9 Channel Stereo Sound Effects.
• I2C networking for up to 4 players.
• Save/Load of games.
• All cheats supported.
• Demos from original WADs run correctly.
• USB Keyboard Input support.
• All end scenes, intermissions, help screens etc. supported.
• Good frame rate; generally 30-35+ FPS.
• Uses 270Mhz overclock (requires flash chip that will run at 135Mhz)

Building

RP2040 Doom should build fine on Linux and macOS. The RP2040 targeting builds should also work on Windows, though I haven't tried.

The build uses CMake.

Regular chocolate-doom/native builds

To build everything, assuming you have SDL2 dependencies installed, you can create a build directory:

mkdir build
cd build
cmake ..

And then run make or make -j<num_cpus> from that directory. To build a particular target e.g. chocolate-doom, do make chocolate-doom

Note this is the way you build the whd_gen tool too.

RP2040 Doom builds

You must have pico-sdk and the latest version of pico-extras installed, along with the regular pico-sdk requisites (e.g. arm-none-eabi-gcc). If in doubt, see the Raspberry Pi documentation. I have been building against the develop branch of pico-sdk, so I recommend that..

NOTE: I was building with arm-none-eabi-gcc 9.2.1 .. it seems like other versions may cause problems with binary size, so stick with that for now.

For USB keyboard input support, RP2040 Doom currently uses a modified version of TinyUSB included as a submodule. Make sure you have initialized this submodule via git submodule update --init

You can create a build directly like this:

mkdir rp2040-build
cd rp2040-build
cmake -DCMAKE_BUILD_TYPE=MinSizeRel -DPICO_BOARD=vgaboard -DPICO_SDK_PATH=/path/to/pico-sdk -DPICO_EXTRAS_PATH=/path/to/pico-extras ..

Note that the PICO_BOARD setting is for the standard VGA demo board which has RGB on pins 0->15, sync pins on 16,17 and I2S on 26,27,28.

As before, use make or make <target> to build.

The RP2040 version has four targets, each of which create a similarly named UF2 file (e.g. doom_tiny.uf2). These UF2 files contain the executable code/data, but they do not contain the WAD data which is converted into a RP2040 Domom specific WHD/WHX format by whd_gen (for more see below). The WHD/WHX file must also be loaded onto the device at a specific address which varies by binary.

"super-tiny" refers to RP2040 Doom builds that use the more compressed WHX format, and required forDOOM1. WAD to run on a 2M Raspberry Pi Pico. "Non super-tiny" refers to RP2040 Doom builds that use the WHD format which is larger, but also is required for Ultimate Doom and Doom II WADs. These binaries are distinct as supporting both formats in the same binary would just have made things bigger and slower.

• doom_tiny This is a "super tiny" version with no USB keyboard support. You can use SDL Event Forwarder to tunnel keyboard input from your host computer over UART. The WHX file must be loaded at 0x10040000.
• doom_tiny_usb This is a "super tiny" version with additional USB keyboard support. Because of the extra USB code, the WHX file must be loaded at 0x10042000. As you can see USB support via TinyUSB causes the binary to grow by 2K (hence the move of the WHX file address) leaving less space for saved games (which are also stored in flash).
• doom_tiny_nost This is a "non super tiny" version of doom_tiny supporting larger WADs stored as WHD. The WHD file must be loaded at 0x10048000
• doom_tiny_nost_usb This is a "non super tiny" version of doom_tiny_usb supporting larger WADs stored as WHD. The WHD file must be loaded at 0x10048000

You can load you WHD/WHX file using picotool. e.g.

picotool load -v -t bin doom1.whx -o 0x10042000.

See whd_gen further below for generating WHX or WHD files.

USB keyboard support

Note that TinyUSB host mode support for keyboard may not work with all keyboards especially since the RP2040 Doom has been built with small limits for number/sizes of hubs etc. I know that Raspberry Pi keyboards work fine, as did my ancient Dell keyboard. Your keyboard may just do nothing, or may cause a crash. If so, for now, you are stuck forwarding keys from another PC via sdl_event_forwarder.

RP2040 Doom builds not targeting an RP2040 device

You can also build the RP2040 Doom to run on your host computer (Linux or macOS) by using pico_host_sdl which simulates RP2040 based video/audio output using SDL.

This version currently embeds the WHD/WHX in src/tiny.whd.h so you must generate this file.

You can do this via ./cup.sh <whd/whx_file>

mkdir host-build
cd host-build
cmake -DPICO_PLATFORM=host -DPICO_SDK_PATH=/path/to/pico-sdk -DPICO_EXTRAS_PATH=/path/to/pico-extras -DPICO_SDK_PRE_LIST_DIRS=/path/to/pico_host_sdl ..

... and then make as usual.

whd_gen

doom1.whx is includd in this repository, otherwise you need to build whd_gen using the regular native build instructions above.

To generate a WHX file (you must use this to convert DOOM1.WAD to run on a 2M Raspberry Pi Pico)

whd_gen <wad_file> <whx_file>

The larger WADs (e.g. Ultimate Doom or Doom II have levels which are too complex to convert into a super tiny WHX file. These larger WADs are not going to fit in a 2M flash anywy, so the less compressed WHD format can be used given that the device now probably has 8M of flash.

whd_gen <wad_file> <whd_file> -no-super-tiny

Note that whd_gen has not been tested with a wide variety of WADs, so whilst it is possible that non Id WADs may work, it is by no means guaranteed!

NOTE: You should use a release build of whd_gen for the best sound effect fidelity, as the debug build deliberately lowers the encoding quality for the sake of speed.

Running the RP2040 version

The releases here use pins as defined when building with PICO_BOARD=vgaboard:

 0-4:    Red 0-4
 6-10:   Green 0-4
 11-15:  Blue 0-4
 16:     HSync
 17:     VSync
 18:     I2C1 SDA
 19:     I2C1 SCL
 20:     UART1 TX
 21:     UART1 RX
 26:     I2S DIN
 27:     I2S BCK
 28:     I2S LRCK

You can always find these from your ELF or UF2 with

picotool info -a <filename>

These match for example the Pimoroni Pico VGA Demo Base which itself is based on the suggested Raspberry Pi Documentation here and the design files zipped here.

Future

Evilution and Plutonia are not yet supported. There is an issue tracking it here.

RP2040 Doom Licenses

• Any code derived from chocolate-doom matinains its existing license (generally GPLv2).
• New RP2040 Doom specific code not implementing existing chocolate-doom interfaces is licensed BSD-3.
• ADPCM-XA is unmodified and is licensed BSD-3.
• Modified emu8950 derived code retains its MIT license.