Comment by junon

Comment by junon 7 days ago

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Very cool. Having done a bit of NES dev I can imagine this wasn't super straightforward to make performant for the graphics, given you can typically only have a few sprites on a row before the NES starts to 'dissolve' them (not sure the term).

I wonder if it's using the background tile map for this instead of sprites, though that's also an impressive amount of graphics bandwidth.

> with full audio playback rate (44.2kHz)

The audio being so clear is also impressive, is that something that the card extends? IIRC the PCM channel on the NES isn't anywhere near that bitrate, and is also 8-bit sample size.

Dylan16807 6 days ago

The channel can either play back delta-modulation samples from memory, or you can directly set the output as a 7 bit value.

So by burning a lot of CPU cycles, you can keep up a perfectly good sample rate using the latter method.

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godd2 6 days ago

The bitrate of the PCM is determined based on how quickly you can write a byte to the register. The fastest you could write general data is once every 6 cycles, which gives ~298 MHz of sample rate, so 44.2 kHz is easily doable if that's all you want to do with the CPU.

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  • junon 4 days ago

    Do you mean 298 KHz? I thought the 6502 on the NES was slightly over 1MHz

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godd2 6 days ago

> I wonder if it's using the background tile map for this instead of sprites

Yes, it's all background tiles being loaded continuously from the SD card. We created the tiles with a custom tile de-maker.

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