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⌂ ∞ Elite on the BBC Micro and NES

Utility routines: UpdateNMITimer

[NES version, Bank 7]

       Name: UpdateNMITimer                                          [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: Update the NMI timer, which we can use to keep track of time for
             places like the combat demo

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * NMI calls UpdateNMITimer




.UpdateNMITimer

 DEC nmiTimer           ; Decrement the NMI timer counter, so that it counts
                        ; each NMI interrupt

 BNE nmit1              ; If it hasn't reached zero yet, jump to nmit1 to return
                        ; from the subroutine

 LDA #50                ; Wrap the NMI timer round to start counting down from
 STA nmiTimer           ; 50 once again, as it just reached zero

 LDA nmiTimerLo         ; Increment (nmiTimerHi nmiTimerLo)
 CLC
 ADC #1
 STA nmiTimerLo
 LDA nmiTimerHi
 ADC #0
 STA nmiTimerHi

.nmit1

 RTS                    ; Return from the subroutine