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⌂ ∞ Elite on the BBC Micro and NES

Drawing ships: LL9_b1

[NES version, Bank 7]

       Name: LL9_b1                                                  [Show more]
       Type: Subroutine
   Category: Drawing ships
    Summary: Call the LL9 routine in ROM bank 1
  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:
             * DrawShipInBitplane calls LL9_b1
             * Main flight loop (Part 12 of 16) calls LL9_b1




.LL9_b1

 LDA currentBank        ; If ROM bank 1 is already paged into memory, jump to
 CMP #1                 ; bank3
 BEQ bank3

 PHA                    ; Otherwise store the current bank number on the stack

 LDA #1                 ; Page ROM bank 1 into memory at $8000
 JSR SetBank

 JSR LL9                ; Call LL9, 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

.bank3

 JMP LL9                ; Call LL9, which is already paged into memory, and
                        ; return from the subroutine using a tail call