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⌂ ∞ ▽ Elite on the 6502

Flight: hyp

[Commodore 64 version]

       Name: hyp                                                     [Show more]
       Type: Subroutine
   Category: Flight
    Summary: Start the hyperspace process

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TT102 calls hyp
             * TTX110 calls via TTX111




 Called when "H" or CTRL-H is pressed during flight. Checks the following:

   * We are in space

   * We are not already in a hyperspace countdown

 If CTRL is being held down, we jump to Ghy to engage the galactic hyperdrive,
 otherwise we check that:

   * The selected system is not the current system

   * We have enough fuel to make the jump

 and if all the pre-jump checks are passed, we print the destination on-screen
 and start the countdown.



 Other entry points:

   TTX111               Used to rejoin this routine from the call to TTX110



.hyp

 LDA QQ12               ; If we are docked (QQ12 = $FF) then jump to dockEd to
 BNE dockEd             ; print an error message and return from the subroutine
                        ; using a tail call (as we can't hyperspace when docked)

 LDA QQ22+1             ; Fetch QQ22+1, which contains the number that's shown
                        ; on-screen during hyperspace countdown

 BEQ P%+3               ; If it is zero, skip the next instruction

 RTS                    ; The count is non-zero, so return from the subroutine

;LDA #CYAN              ; These instructions are commented out in the original
;JSR DOCOL              ; source

 JSR CTRL               ; Scan the keyboard to see if CTRL is currently pressed

 BMI Ghy                ; If it is, then the galactic hyperdrive has been
                        ; activated, so jump to Ghy to process it

 LDA QQ11               ; If the current view is 0 (i.e. the space view) then
 BEQ TTX110             ; jump to TTX110, which calls TT111 to set the current
                        ; system to the nearest system to (QQ9, QQ10), and jumps
                        ; back into this routine at TTX111 below

 AND #%11000000         ; If either bit 6 or 7 of the view type is set - so
 BNE P%+3               ; this is either the Short-range or Long-range Chart -
                        ; then skip the following instruction

 RTS                    ; This is not a chart view, so return from the
                        ; subroutine

 JSR hm                 ; This is a chart view, so call hm to redraw the chart
                        ; crosshairs

.TTX111

                        ; If we get here then the current view is either the
                        ; space view or a chart

 LDA QQ8                ; If either byte of the distance to the selected system
 ORA QQ8+1              ; in QQ8 are zero, skip the next instruction to make a
 BNE P%+3               ; copy of the destination seeds in safehouse

 RTS                    ; The selected system is the same as the current system,
                        ; so return from the subroutine

 LDX #5                 ; We now want to copy those seeds into safehouse, so we
                        ; so set a counter in X to copy 6 bytes

.sob

 LDA QQ15,X             ; Copy the X-th byte of QQ15 into the X-th byte of
 STA safehouse,X        ; safehouse

 DEX                    ; Decrement the loop counter

 BPL sob                ; Loop back to copy the next byte until we have copied
                        ; all six seed bytes

 LDA #7                 ; Move the text cursor to column 7
 JSR DOXC

 LDA #23                ; Set A = 23 to use as the text row for views other
                        ; than the space view

 LDY QQ11               ; If QQ11 = 0 then this is the space view, so set A = 17
 BNE P%+4               ; to use as the text row
 LDA #17

 JSR DOYC               ; Move the text cursor to row 17 (in the space view) or
                        ; 23 (otherwise), which is in the middle of the bottom
                        ; text row)

 LDA #0                 ; Set QQ17 = 0 to switch to ALL CAPS
 STA QQ17

 LDA #189               ; Print recursive token 29 ("HYPERSPACE ")
 JSR TT27

 LDA QQ8+1              ; If the high byte of the distance to the selected
 BNE goTT147            ; system in QQ8 is > 0, then it is definitely too far to
                        ; jump (as our maximum range is 7.0 light years, or a
                        ; value of 70 in QQ8(1 0)), so jump to TT147 via goTT147
                        ; to print "RANGE?" and return from the subroutine using
                        ; a tail call

 LDA QQ14               ; Fetch our current fuel level from Q114 into A

 CMP QQ8                ; If our fuel reserves are greater than or equal to the
 BCS P%+5               ; distance to the selected system, then we have enough
                        ; fuel for this jump, so skip the following instruction
                        ; to start the hyperspace countdown

.goTT147

 JMP TT147              ; We don't have enough fuel to reach the destination, so
                        ; jump to TT147 to print "RANGE?" and return from the
                        ; subroutine using a tail call

 LDA #'-'               ; Print a hyphen
 JSR TT27

 JSR cpl                ; Call cpl to print the name of the selected system

                        ; Fall through into wW to start the hyperspace countdown