Sound
Sound support is done with another OS call, OSWORD, which handles a variety of tasks enumerated via a task code placed into the accumulator. All OSWORD calls bear a parameter block used to send and receive multiple data, passed into the X and Y registers. There are four buffered sound channels -- three melodic and one noise -- based on the sound chip found in the BBC Micro. There is only one waveform for melodic channels; the supported note parameters are pitch, duration, and amplitude. The amplitude parameter is normally negative; positive values select an envelope (a predefined temporal variation) to apply to the note.
Other meta parameters (passed through the channel code when using the SOUND command in BASIC) include flush (the buffer is cleared and the channel silenced before the note is played), synchronise count (as soon as the same synch count is received for that many channels, all the synchronised notes are played together), and control over the Speech system upgrade where fitted.
Read more about this topic: Acorn MOS
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—Henry David Thoreau (1817–1862)