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46 lines
2.6 KiB
Markdown
46 lines
2.6 KiB
Markdown
# Seta/Allumer X1-010
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One of sound chip originally designed by Seta, mainly used at their arcade hardwares at late-80s to early-2000s.
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it has 2 output channel, but no known hardware using this feature for stereo sound.
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later hardware paired this with external bankswitching logic, but its logic is not emulated now in current furnace revision.
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Allumer one is just rebadged Seta's thing for use in their arcade hardwares.
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It has 16 channels, and all channels can be switchable to PCM sample or wavetable playback mode.
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Wavetable needs to paired with envelope, this feature is similar as AY PSG but it's shape are stored at RAM: it means it is user-definable.
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In furnace, this chip is can be configurable for original arcade mono output or stereo output - its simulates early 'incorrect' emulation on some mono hardware but it is also based on the assumption that each channel is connected to each output.
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# waveform type
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This chip supports 2 type waveforms, needs to paired external 8KB RAM for use these feature:
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One is signed 8 bit mono waveform, its operated like other wavetable based sound systems.
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These are stored at bottom half of RAM at common case.
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Another one ("Envelope") is 4 bit stereo waveform, its multiplied with above and calculates final output, Each nibble is used for each output channels.
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These are stored at upper half of RAM at common case.
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Both waveforms are 128 byte fixed size, its freely allocated at each half of RAM except channel register area: each half can be stored total 32/31 waveforms at once.
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# effects
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- `10xx`: change wave.
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- `11xx`: change envelope shape. (also wavetable)
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- `17xx`: toggle PCM mode.
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- `20xx`: set PCM frequency. (1 to FF)*
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- `22xx`: set envelope mode.
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- bit 0 sets whether envelope will affect this channel.
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- bit 1 sets whether envelope one-shot mode. when it sets, channel is halted after envelope cycle is ended.
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- bit 2 sets whether envelope shape split mode. when it sets, envelope shape will splitted to left half and right half.
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- bit 3/5 sets whether the right/left shape will mirror the original one.
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- bit 4/6 sets whether the right/left output will mirror the original one.
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- `23xx`: set envelope period.
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- `25xx`: slide envelope period up.
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- `26xx`: slide envelope period down.
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- `29xy`: enable auto-envelope mode.
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- in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
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- `x` is the numerator.
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- `y` is the denominator.
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- if `x` or `y` are 0 this will disable auto-envelope mode.
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* PCM frequency: 255 step, fomula: `step * (Chip clock / 8192)`; 1.95KHz to 498KHz if Chip clock is 16MHz.
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