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⌂ ∞ Elite on the BBC Micro and NES

Sound: MakeMusic

[NES version, Bank 6]

       Name: MakeMusic                                               [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Play the current music on the SQ1, SQ2, TRI and NOISE channels
  Deep dive: Music in NES Elite

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * MakeSounds calls MakeMusic




.MakeMusic

 LDA enableSound        ; If enableSound is non-zero then sound is enabled, so
 BNE makm1              ; jump to makm1 to play the current music

 RTS                    ; Otherwise sound is disabled, so return from the
                        ; subroutine

.makm1

 LDA tuneSpeed          ; Set tuneProgress = tuneProgress + tuneSpeed
 CLC                    ;
 ADC tuneProgress       ; This moves the tune along by the current speed,
 STA tuneProgress       ; setting the C flag only when the addition of this
                        ; iteration's speed overflows the addition
                        ;
                        ; This ensures that we only send music to the APU once
                        ; every 256 / tuneSpeed iterations, which keeps the
                        ; music in sync and sends the music more regularly with
                        ; higher values of tuneSpeed

 BCC makm2              ; If the addition didn't overflow, jump to makm2 to skip
                        ; playing music in this VBlank

 JSR MakeMusicOnSQ1     ; Play the current music on the SQ1 channel

 JSR MakeMusicOnSQ2     ; Play the current music on the SQ2 channel

 JSR MakeMusicOnTRI     ; Play the current music on the TRI channel

 JSR MakeMusicOnNOISE   ; Play the current music on the NOISE channel

.makm2

 JSR ApplyEnvelopeSQ1   ; Apply volume and pitch changes to the SQ1 channel

 JSR ApplyEnvelopeSQ2   ; Apply volume and pitch changes to the SQ2 channel

 JSR ApplyEnvelopeTRI   ; Apply volume and pitch changes to the TRI channel

 JMP ApplyEnvelopeNOISE ; Apply volume and pitch changes to the NOISE channel,
                        ; returning from the subroutine using a tail call