The wW subroutine - Elite on the 6502

       Name: wW                                                      [Show more]
       Type: Subroutine
   Category: Flight
    Summary: Start a hyperspace countdown
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Ghy calls via wW2


 Start the hyperspace countdown (for both inter-system hyperspace and the
 galactic hyperdrive).


 Other entry points:

   wW2                  Start the hyperspace countdown, starting the countdown
                        from the value in A


.wW

 LDA #15                ; The hyperspace countdown starts from 15, so set A to
                        ; 15 so we can set the two hyperspace counters

.wW2

 STA QQ22+1             ; Set the number in QQ22+1 to A, which is the number
                        ; that's shown on-screen during the hyperspace countdown

 STA QQ22               ; Set the number in QQ22 to 15, which is the internal
                        ; counter that counts down by 1 each iteration of the
                        ; main game loop, and each time it reaches zero, the
                        ; on-screen counter gets decremented, and QQ22 gets set
                        ; to 5, so setting QQ22 to 15 here makes the first tick
                        ; of the hyperspace counter longer than subsequent ticks

 TAX                    ; Print the 8-bit number in X (i.e. 15) at text location
 JMP ee3                ; (0, 1), padded to 5 digits, so it appears in the top
                        ; left corner of the screen, and return from the
                        ; subroutine using a tail call

;.hy5                   ; This instruction and the hy5 label are commented out
;RTS                    ; in the original - they can actually be found at the
                        ; end of the jmp routine below, so perhaps this is where
                        ; they were originally, but the authors realised they
                        ; could save a byte by using a tail call instead of an
                        ; RTS?
Flight: wW

[Commodore 64 version]
