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⌂ ∞ Elite on the BBC Micro and NES

Flight: hyp

[NES version, Bank 0]

       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




 Called when the hyperspace icon is chosen during flight. Checks the following:

   * We are in space

   * We are not already in a hyperspace countdown

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



.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 selectedSystemFlag ; If bit 6 of selectedSystemFlag is set, then we can
 ASL A                  ; hyperspace to the currently selected system, so jump
 BMI hyps1              ; to hyps1 to skip the following instruction and keep
                        ; going

 RTS                    ; Bit 6 of selectedSystemFlag is clear, so we can't
                        ; hyperspace to the currently selected system (we may
                        ; not have enough fuel, or it might be the same as the
                        ; current system), so return from the subroutine

.hyps1

 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