OpenDSP

An open-source replacement for dspfirm.cdc, the DSP firmware that libctru's ndsp needs on the Nintendo 3DS.

Normally, a homebrew app with sound only works after the user has dumped dspfirm.cdc from their console onto the SD card. OpenDSP gets linked into your app instead, so there is nothing to dump and nothing to copy. ndsp works as before. You only call opendspInit() instead of ndspInit().

OpenDSP was written from scratch and contains no code from Nintendo's firmware.

Usage

Build and install the library (devkitPro with libctru required):

make -C library install

In your Makefile:

LIBS    := -lopendsp -lctru -lm
LIBDIRS := $(PORTLIBS) $(CTRULIB)

In your code:

#include <opendsp.h>

opendspInit();   // instead of ndspInit()
...
opendspExit();   // instead of ndspExit()

More details and other ways to integrate it are in docs/GUIDE.md.

Reverb and delay

OpenDSP also has a reverb and a delay that run on the DSP, on ndsp's two aux buses. Voices send to them with the usual mix gains, and ndspAuxSetVolume() brings the result back.

#include <opendsp/effects.h>

opendspReverbConfig hall = {
    .struct_size = sizeof(hall),
    .room_size = 0.9f, .decay_time = 2.5f, .damping = 0.35f,
    .diffusion = 0.75f, .width = 1.0f, .level = 0.7f,
};
opendspReverbSet(0, &hall);
ndspAuxSetVolume(0, 0.7f);

See docs/GUIDE.md for the delay and what it all costs.

Status

Supported: 24 voices, PCM8/PCM16 (mono and stereo), DSP-ADPCM, looping wave buffers, playback rates up to 4x, all three interpolation modes, the per-voice filters, mix gains, the aux settings, master volume, output modes, clipping, capture and sleep mode. Plus the reverb and delay above.

Missing: AAC decoding. Surround output is mixed down to stereo, though the rear ratio works.

Tested on a New 3DS with Luma3DS.

Demo

examples/soundlab is a small app with music, sound effects, a WAV player, mixer settings and a reverb and delay page. The DSP lab shows how busy the DSP is. All of it runs on OpenDSP.

Building the firmware

The library already contains a prebuilt firmware/opendsp.cdc. You only have to build it yourself if you want to change the firmware. See docs/BUILDING.md.

License

BSD 2-Clause. If you ship OpenDSP inside a binary, include the copyright notice and the license text in your credits or documentation.

Made by Cellenseres. Thanks to Gericom for teak-llvm, wwylele for teakra, and the devkitPro and libctru developers.

OpenDSP is not affiliated with Nintendo.