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⌂ ∞ Elite on the BBC Micro and NES

Drawing the screen: SetupViewInNMI_b3

[NES version, Bank 7]

       Name: SetupViewInNMI_b3                                       [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Call the SetupViewInNMI 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:
             * SetSpaceViewInNMI calls SetupViewInNMI_b3




.SetupViewInNMI_b3

 LDA #%11000000         ; Set A to the bitplane flags to set for the drawing
                        ; bitplane in the call to SetupViewInNMI below:
                        ;
                        ;   * Bit 2 clear = send tiles up to configured numbers
                        ;   * Bit 3 clear = don't clear buffers after sending
                        ;   * Bit 4 clear = we've not started sending data yet
                        ;   * Bit 5 clear = we have not yet sent all the data
                        ;   * Bit 6 set   = send both pattern and nametable data
                        ;   * Bit 7 set   = send data to the PPU
                        ;
                        ; Bits 0 and 1 are ignored and are always clear

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

 LDA currentBank        ; If ROM bank 3 is already paged into memory, jump to
 CMP #3                 ; bank18
 BEQ bank18

 PHA                    ; Otherwise store the current bank number on the stack

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

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

 JSR SetupViewInNMI     ; Call SetupViewInNMI, 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

.bank18

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

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