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⌂ ∞ ▽ Revs on the BBC Micro

Sound: DefineEnvelope

       Name: DefineEnvelope                                          [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Define a sound envelope

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ProcessShiftedKeys calls DefineEnvelope
             * ResetVariables calls DefineEnvelope




 Arguments:

   A                    The offset of the sound envelope data in envelopeData:

                          * A = 0 for the first (and only) envelope definition



 Returns:

   X                    X is unchanged



.DefineEnvelope

 STX xStoreSound        \ Store the value of X in xStoreSound, so we can
                        \ preserve it through the call to the DefineEnvelope
                        \ routine

 CLC                    \ Set (Y X) = envelopeData + A
 ADC #LO(envelopeData)  \
 TAX                    \ starting with the low byte

 LDA #8                 \ Set A = 8 for the OSWORD command to define an envelope

                        \ Fall through into MakeSoundEnvelope to set up Y and
                        \ apply the OSWORD command to the (Y X) block, which
                        \ defines the relevant sound envelope