GameCube Architecture: Powerful and Compact by Rodrigo Copetti

Author:Rodrigo Copetti [Copetti, Rodrigo]
Language: eng
Format: epub
Tags: Nonfiction, Computers, Advanced Computing, Engineering, Computer Architecture, Application Software, Computer Graphics, Computer Science
ISBN: 9798201660857
Amazon: B0B6G9Z4BC
Goodreads: 62908910
Published: 2019-11-18T14:30:00+00:00

6 Audio

Nintendo finally delivered some dedicated audio circuitry to offload the huge task from the CPU-GPU and provide richer sounds. Their new solution is an independent Digital Signal Processor or ‘DSP’ manufactured by Macronix running inside Flipper.

The DSP’s job consists of performing different operations over our raw audio data (e.g. volume changes, sample rate conversion, 3D sound effects, filtering, echo, reverb, etc) and then output a 2-channel PCM signal. It doesn’t work alone however, the DSP delivers audio with the help of other components.

Its first companion is the Audio Interface (AI), a 16-bit stereo digital-to-analogue converter responsible for sending the final sample through the audio signal that ends on the TV. The AI can only process 32 bytes of audio data every 0.25ms, so if we take into account that each sound sample weights 2 bytes and we need two to create stereo sound, the AI will be able to mix up to eight stereo samples with up to 32 kHz of sampling rate, sound!

Finally, we have the Audio RAM (ARAM) block, which is a large (16 MB) but very slow spare memory that can be used to store raw sound data. There’s quite a lot of space, so the GPU can also use it to store additional material (like textures). The CPU doesn’t have direct access to this memory so it will resort to DMA to move content around.

For better or worse, the DSP is programmable with the use of microcode (yikes), but fear not, as the official SDK already bundles a general-purpose microcode that almost every game used, except on the console’s boot sequence and some Nintendo games (how convenient, as Nintendo didn’t document the DSP, so only they know how to program it).

That being said, the process of generating sound works as follows [11]:

CPU commands DMA to move raw samples to ARAM.

CPU sends a list of commands that instruct how the DSP should operate these samples. In other words, it uploads the microcode program (only one is officially available for developers).

DSP fetches samples from ARAM, applies the required operations and mixes them into two channels. Finally, it stores the resulting data on RAM.

AI fetches processed samples from RAM and outputs them through the audio signal.

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