audio

Documentation

Overview

Package audio implements the audio generation of the TIA. Originally, Gopher2600 used Ron Fries' audio implementation but this has now been completely superceded by the work of Chris Brenner.

Chris's work has been used in both the 6502.ts and Stella projects. Source from both projects was used as reference. Both projects are exactly equivalent.

  6502.ts (published under the MIT licence)
		https://github.com/6502ts/6502.ts/blob/6f923e5fe693b82a2448ffac1f85aea9693cacff/src/machine/stella/tia/PCMAudio.ts
		https://github.com/6502ts/6502.ts/blob/6f923e5fe693b82a2448ffac1f85aea9693cacff/src/machine/stella/tia/PCMChannel.ts

 Stella (published under the GNU GPL v2.0 licence)
		https://github.com/stella-emu/stella/blob/e6af23d6c12893dd17711002971087f28f87c31f/src/emucore/tia/Audio.cxx
		https://github.com/stella-emu/stella/blob/e6af23d6c12893dd17711002971087f28f87c31f/src/emucore/tia/AudioChannel.cxx

Index

• Constants
• func CmpRegisters(a Registers, b Registers) bool
• type Audio
  • func NewAudio(env *environment.Environment) *Audio
  • func (au *Audio) HasTicked() (bool, bool, bool)
  • func (au *Audio) Plumb(env *environment.Environment)
  • func (au *Audio) ReadMemRegisters(data chipbus.ChangedRegister) bool
  • func (au *Audio) Reset()
  • func (au *Audio) SetTracker(tracker Tracker)
  • func (au *Audio) Snapshot() *Audio
  • func (au *Audio) Step() bool
  • func (au *Audio) String() string
  • func (au *Audio) UpdateTracker()
• type Registers
  • func (reg Registers) String() string
• type Tracker
• type TrackerEnvironment

Constants

const SampleFreq = 31400

SampleFreq represents the number of samples generated per second. This is the 30Khz reference frequency desribed in the Stella Programmer's Guide.

Functions

func CmpRegisters

func CmpRegisters(a Registers, b Registers) bool

CmpRegisters returns true if the two registers contain the same values

Types

type Audio

type Audio struct {

	// the volume output for each channel
	Vol0 uint8
	Vol1 uint8
	// contains filtered or unexported fields
}

Audio is the implementation of the TIA audio sub-system, using Ron Fries' method. Reference source code here:

https://raw.githubusercontent.com/alekmaul/stella/master/emucore/TIASound.c

func NewAudio

func NewAudio(env *environment.Environment) *Audio

NewAudio is the preferred method of initialisation for the Audio sub-system.

func (*Audio) HasTicked

func (au *Audio) HasTicked() (bool, bool, bool)

HasTicked returns whether the audio channels were ticked on the previous video cycle. The return values indicate the ticking for phase 0 & phase 1; and whether an audio register has changed. Can never return three true values

The function is only useful for emulator reflection.

func (*Audio) Plumb

func (au *Audio) Plumb(env *environment.Environment)

Plumb audio into emulation

func (*Audio) ReadMemRegisters

func (au *Audio) ReadMemRegisters(data chipbus.ChangedRegister) bool

ReadMemRegisters checks the TIA memory for changes to registers that are interesting to the audio sub-system

Returns true if memory.ChipData has not been serviced.

func (*Audio) Reset

func (au *Audio) Reset()

func (*Audio) SetTracker

func (au *Audio) SetTracker(tracker Tracker)

SetTracker adds a Tracker implementation to the Audio sub-system.

func (*Audio) Snapshot

func (au *Audio) Snapshot() *Audio

Snapshot creates a copy of the TIA Audio sub-system in its current state.

func (*Audio) Step

func (au *Audio) Step() bool

Step the audio on one TIA clock. The step will be filtered to produce a 30Khz clock.

func (*Audio) String

func (au *Audio) String() string

func (*Audio) UpdateTracker

func (au *Audio) UpdateTracker()

UpdateTracker changes the state of the attached tracker. Should be called whenever any of the audio registers have changed.

type Registers

type Registers struct {
	Control uint8 // 4 bit
	Freq    uint8 // 5 bit
	Volume  uint8 // 4 bit
}

each channel has three registers that control its output. from the "Stella Programmer's Guide":

"Each audio circuit has three registers that control a noise-tone generator (what kind of sound), a frequency selection (high or low pitch of the sound), and a volume control."

not all the bits are used in each register. the comments below indicate how many of the least-significant bits are used.

func (Registers) String

func (reg Registers) String() string

type Tracker

type Tracker interface {
	// AudioTick is called every video cycle
	AudioTick(env TrackerEnvironment, channel int, reg Registers)
}

Tracker implementations display or otherwise record the state of the audio registers for each channel.

type TrackerEnvironment

type TrackerEnvironment interface {
	IsEmulation(environment.Label) bool
}

TrackerEnvironment defines the subset of the Environment type required by a Tracker implementation