Drawing the screen: ClearScreen_b3

       Name: ClearScreen_b3                                          [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Call the ClearScreen routine in ROM bank 3
  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:
             * BAY calls ClearScreen_b3
             * TBRIEF calls ClearScreen_b3
             * TT66 calls ClearScreen_b3


.ClearScreen_b3

 LDA currentBank        ; If ROM bank 3 is already paged into memory, jump to
 CMP #3                 ; bank27
 BEQ bank27

 PHA                    ; Otherwise store the current bank number on the stack

 LDA #3                 ; Page ROM bank 3 into memory at $8000
 JSR SetBank

 JSR ClearScreen        ; Call ClearScreen, 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

.bank27

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