Sound: MakeSoundEnvelope

       Name: MakeSoundEnvelope                                       [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Either make a sound or set up an envelope
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * MakeSound calls MakeSoundEnvelope


 Arguments:

   A                    The action:

                          * A = 7 make a sound

                          * A = 8 to define a sound envelope

   X                    The low byte of the address of the OSWORD block

   C flag               The outcome of the addition of the low bytes of (Y X)


.MakeSoundEnvelope

 LDY #HI(envelopeData)  \ Set y to the high byte of the envelopeData block
                        \ address, so (Y X) now points to the relevant envelope
                        \ or sound data block

 BCC senv1              \ If the addition we did before calling the routine
                        \ didn't overflow, skip the next instruction

 INY                    \ The above addition overflowed, so increment the high
                        \ byte of (Y X) to point to the next page in memory

.senv1

 JSR OSWORD             \ Call OSWORD with action A, as follows:
                        \
                        \  * A = 7 to make the sound at (Y X)
                        \
                        \  * A = 8 to set up the sound envelope at (Y X)

 RTS                    \ Return from the subroutine

 NOP                    \ This instruction appears to be unused