Utility routines: ZERO

       Name: ZERO                                                    [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: Reset the local bubble of universe and ship status
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * RES2 calls ZERO
             * RESET calls ZERO


 This resets the following workspaces to zero:

   * WP workspace variables from FRIN to de, which include the ship slots for
     the local bubble of universe, and various flight and ship status
     variables, including the MANY block


.ZERO

 JSR SetupPPUForIconBar ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 LDX #(de-FRIN+1)       ; We're going to zero the WP workspace variables from
                        ; FRIN to de, so set a counter in X for the correct
                        ; number of bytes

 LDA #0                 ; Set A = 0 so we can zero the variables

.ZEL

 STA FRIN-1,X           ; Zero byte X-1 of FRIN to de

 DEX                    ; Decrement the loop counter

 BNE ZEL                ; Loop back to zero the next variable until we have done
                        ; them all from FRIN to FRIN+42

 LDX #NTY               ; We're now going to zero the NTY bytes in the MANY
                        ; block, so set a counter in X for the correct number of
                        ; bytes

.ZEL2

 STA MANY,X             ; Zero the X-th byte of MANY

 DEX                    ; Decrement the loop counter

 BPL ZEL2               ; Loop back to zero the next variable until we have done
                        ; them all from MANY to MANY+33

 JSR SetupPPUForIconBar ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 RTS                    ; Return from the subroutine