Tactics: FRMIS

       Name: FRMIS                                                   [Show more]
       Type: Subroutine
   Category: Tactics
    Summary: Fire a missile from our ship
  Deep dive: The NES combat demo
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main flight loop (Part 3 of 16) calls FRMIS


 We fired a missile, so send it streaking away from us to unleash mayhem and
 destruction on our sworn enemies.


.FRMIS

 LDX #MSL               ; Call FRS1 to launch a missile straight ahead of us
 JSR FRS1

 BCC FR1                ; If FRS1 returns with the C flag clear, then there
                        ; isn't room in the universe for our missile, so jump
                        ; down to FR1 to display a "missile jammed" message

 LDX MSTG               ; Fetch the slot number of the missile's target

 JSR GINF               ; Get the address of the data block for the target ship
                        ; and store it in INF

 LDA FRIN,X             ; Fetch the ship type of the missile's target into A

 JSR ANGRY              ; Call ANGRY to make the target ship hostile

 LDY #133               ; We have just launched a missile, so we need to remove
 JSR ABORT              ; missile lock and hide the active indicator on the
                        ; dashboard by setting it to the pattern number in Y
                        ; (no missile indicator = pattern 133)

 DEC NOMSL              ; Reduce the number of missiles we have by 1

 LDA demoInProgress     ; If the demo is not in progress, jump to frmi1 to skip
 BEQ frmi1              ; the following

                        ; If we get here then the demo is in progress and we
                        ; just fired a missile, so we get a 60-second penalty
                        ; added to the time taken to complete the demo

 LDA #147               ; Print recursive token 146 ("60 SECOND PENALTY") in
 LDY #10                ; the middle of the screen and leave it there for 10
 JSR PrintMessage       ; ticks of the DLY counter

 LDA #25                ; Set nmiTimer = 25 to add half a second on top of the
 STA nmiTimer           ; penalty below (as 25 frames is half a second in PAL
                        ; systems)

 LDA nmiTimerLo         ; Add 60 to (nmiTimerHi nmiTimerLo) so the time recorded
 CLC                    ; to complete the combat demo is 60 seconds longer than
 ADC #60                ; it would have been if we hadn't fired the missile
 STA nmiTimerLo
 BCC frmi1
 INC nmiTimerHi

.frmi1

 LDY #9                 ; Call the NOISE routine with Y = 9 to make the sound
 JMP NOISE              ; of a missile launch, returning from the subroutine
                        ; using a tail call