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⌂ ∞ ▽ Elite on the BBC Micro and NES

Drawing the screen: ChangeToView_b0

[NES version, Bank 7]

       Name: ChangeToView_b0                                         [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Call the ChangeToView routine in ROM bank 0
  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:
             * ShowScrollText calls ChangeToView_b0




.ChangeToView_b0

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

 LDA currentBank        ; If ROM bank 0 is already paged into memory, jump to
 CMP #0                 ; bank12
 BEQ bank12

 PHA                    ; Otherwise store the current bank number on the stack

 LDA #0                 ; Page ROM bank 0 into memory at $8000
 JSR SetBank

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

 JSR ChangeToView       ; Call ChangeToView, 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

.bank12

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

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