ay8910.h File Reference

Go to the source code of this file.

Data Structures
struct	AYChannel
	A AY-3-8910 channel. More...
struct	AYEnvelope
	Envelope of AY-3-8910. More...
struct	AYNoise
	Noise of AY-3-8910. More...
struct	AY8910
	A AY-3-8910 emulator. More...

Macros
#define	AY8910_DECIMATE   3
	Decimation factor for AY8910.
#define	AY8910_OUTPUT_STEREO   1
	Generate stereo output.
#define	AY8910_VOLUME_ATTENUATE   0.8
	Define the global attenuation applied to volumes (range 0.0 - 1.0).
#define	AY8910_CENTER_SILENCE   1
	Generate silence as 0.

Functions
void	ay8910_reset (AY8910 *ay)
	Reset the AY8910 emulator.
void	ay8910_set_ports (AY8910 *ay, uint8_t(*PortRead)(int), void(*PortWrite)(int, uint8_t))
	Configure the I/O port callbacks.
void	ay8910_write_addr (AY8910 *ay, uint8_t addr)
	Write to the AY8910 address line.
void	ay8910_write_data (AY8910 *ay, uint8_t val)
	Write to the AY8910 data line.
uint8_t	ay8910_read_data (AY8910 *ay)
	Read from the AY8910 data line.
bool	ay8910_is_mute (AY8910 *ay)
	Return true if ay8910 is currently muted (all channels disabled)
int	ay8910_gen (AY8910 *ay, int16_t *out, int nsamples)
	Generate audio for the specified number of samples.

Detailed Description

Author

Giovanni Bajo giova.nosp@m.nnib.nosp@m.ajo@g.nosp@m.mail.nosp@m..com

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Data Structure Documentation

AYChannel

struct AYChannel

A AY-3-8910 channel.

Data Fields
uint16_t	tone_period	Period (in ticks) of the current tone.
uint8_t	tone_vol	Volume of the tone (0x10 -> use envelope)
uint8_t	tone_en	Enable flag of the tone (0 is enabled)
uint8_t	noise_en	Enable flag of the noise for this channel (0 is enabled)
uint16_t	count	Current tick count for the period.
uint8_t	out	Current output value for this channel.

AYEnvelope

struct AYEnvelope

Envelope of AY-3-8910.

Data Fields
uint16_t	period	Period (in ticks) of the envelope.
uint8_t	shape	Shape of the envelope (jigsaw, etc.)
uint8_t	attack	0x0 if in attack, 0xF if in the release
uint8_t	alternate	True if attack and release alternate (jigsaw)
uint8_t	hold	True if the envelope holds after attack.
uint16_t	count	Current tick count for the period.
int16_t	step	Current step of the envelope.
uint8_t	vol	Current output volume.
uint8_t	holding	True if the envelope is currently holding.

AYNoise

struct AYNoise

Noise of AY-3-8910.

Data Fields
uint8_t	period	Period (in ticks) of the noise.
uint8_t	count	Current tick count for the period.
uint32_t	out	Current output value.

Macro Definition Documentation

AY8910_DECIMATE

#define AY8910_DECIMATE   3

Decimation factor for AY8910.

AY8910 is usually clocked at a very high frequency (>100K), and thus it requires downsampling to be played back. This emulator offers a very basic downsampling filter via decimation (taking average of Nth consecutive samples) that is usually a good compromise between quality and speed, for realtime playback. It will not sound as good as a real downsampling filter though.

It is suggested to configure this number to the smallest value that brings the AY8910 output frequency within the playback sample rate.

AY8910_OUTPUT_STEREO

#define AY8910_OUTPUT_STEREO   1

Generate stereo output.

If 1, AY8910 will generate a stereo output with fixed pans for each of the three internal channels, similar to what Arkos Tracker 2 does in stereo mode.

AY8910_VOLUME_ATTENUATE

#define AY8910_VOLUME_ATTENUATE   0.8

Define the global attenuation applied to volumes (range 0.0 - 1.0).

The AY8910 often clips so it's important to lower a bit the volume to avoid sound artifacts.

AY8910_CENTER_SILENCE

#define AY8910_CENTER_SILENCE   1

Generate silence as 0.

Normally, AY8910 generates output samples in which the silence is represented by -32768 (minimum volume). This is a little inconvenient if the caller wants to skip generation when the AY8910 is muted for performance reasons, because audio mixers normally assume that muted channels are made by samples with value 0, otherwise disabling the AY8910 would affect the volume of all other channels.

By setting this macro to 1, the dynamic range will be halved in the range 0-32767, so the silence will be as expected, but the audio will be somehow "duller".

Function Documentation

ay8910_gen()

int ay8910_gen	(	AY8910 *	ay,
		int16_t *	out,
		int	nsamples
	)

Generate audio for the specified number of samples.

"nsamples" is the number of samples after decimation (so the exact number of samples written in the output buffer).