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⌂ ∞ Elite on the BBC Micro and NES

Sound: ChooseMusic_b6

[NES version, Bank 7]

       Name: ChooseMusic_b6                                          [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Call the ChooseMusic routine in ROM bank 6
  Deep dive: Splitting NES Elite across multiple ROM banks

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DEATH2 calls ChooseMusic_b6
             * DrawTitleScreen calls ChooseMusic_b6
             * PauseGame calls ChooseMusic_b6
             * TT102 calls ChooseMusic_b6




 Arguments:

   A                    The number of the tune to choose



.ChooseMusic_b6

 PHA                    ; Wait until the next NMI interrupt has passed (i.e. the
 JSR WaitForNMI         ; next VBlank), preserving the value in A via the stack
 PLA

 ORA #%10000000         ; Set bit 7 of the tune number and store in newTune to
 STA newTune            ; indicate that we are now in the process of changing to
                        ; this tune

 AND #%01111111         ; Clear bit 7 to set A to the tune number once again

 LDX disableMusic       ; If music is disabled then bit 7 of disableMusic will
 BMI RTS4               ; be set, so jump to RTS4 to return from the subroutine
                        ; as we can't choose a new tune if music is disabled

 STA storeA             ; Store the value of A so we can retrieve it below

 LDA currentBank        ; If ROM bank 6 is already paged into memory, jump to
 CMP #6                 ; bank1
 BEQ bank1

 PHA                    ; Otherwise store the current bank number on the stack

 LDA #6                 ; Page ROM bank 6 into memory at $8000
 JSR SetBank

 LDA storeA             ; Restore the value of A that we stored above

 JSR ChooseMusic        ; Call ChooseMusic, now that it is paged into memory

 JMP ResetBank          ; Fetch the previous ROM bank number from the stack and
                        ; page that bank back into memory at $8000, returning
                        ; from the subroutine using a tail call

.bank1

 LDA storeA             ; Restore the value of A that we stored above

 JMP ChooseMusic        ; Call ChooseMusic, which is already paged into memory,
                        ; and return from the subroutine using a tail call