47 lines
1.4 KiB
Go
47 lines
1.4 KiB
Go
package audio
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// Very simple implementation of audio. Every frame, a channel is filled with
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// all the audio samples from the last frame. Each time the speaker clicks, the
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// channel is filled with the last audio samples. The channel is also
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// filled at the end of the frame.
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import "github.com/freewilll/apple2-go/system"
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// Click handles a speaker click
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func Click() {
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ForwardToFrameCycle()
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system.AudioAttenuationCounter = 400
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system.LastAudioValue = ^system.LastAudioValue
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}
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// attenuate makes sure the audio goes down to zero after a period of inactivity
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func attenuate(sample int16) int16 {
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if system.AudioAttenuationCounter == 0 {
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return 0
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}
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system.AudioAttenuationCounter--
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return sample
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}
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// ForwardToFrameCycle calculates how many audio samples need to be written to
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// the channel based on how many CPU cycles have been executed since the last
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// flush and shove them into the channel.
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func ForwardToFrameCycle() {
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// 1023000/44100=23.19 cycles per audio sample
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cyclesPerAudioSample := system.CPUFrequency / float64(system.AudioSampleRate)
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// Should be about 1023000/60=17050
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elapsedCycles := system.FrameCycles - system.LastAudioCycles
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// Should be about 17050/23.19=735 audio samples per frame
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audioSamples := uint64(float64(elapsedCycles) / cyclesPerAudioSample)
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for i := uint64(0); i < audioSamples; i++ {
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b := attenuate(system.LastAudioValue)
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system.AudioChannel <- b
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}
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system.LastAudioCycles = system.FrameCycles
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}
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