Version analysis of ZERO - Elite on the BBC Micro and NES

This code appears in the following versions (click to see it in the source code):

Cassette, Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron

Code variations between these versions are shown below.

       Name: ZERO
       Type: Subroutine
   Category: Utility routines

Code variation 1 of 3A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Electron
Flight, Docked, 6502SP, Master
    Summary: Zero-fill pages &9, &A, &B, &C and &D
    Summary: Reset the local bubble of universe and ship status



 This resets the following workspaces to zero:

Code variation 2 of 3A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette
Flight, Docked
6502SP, Master
Electron
   * The ship data blocks ascending from K% at &0900

   * The ship line heap descending from WP at &0D40

   * 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
     (only a portion of the LSX/LSO sun line heap is cleared)
   * 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
     (only a portion of the LSX/LSO sun line heap is cleared)
   * UP workspace variables from FRIN to de, which include the ship slots for
     the local bubble of universe, and various flight and ship status variables
   * The ship data blocks ascending from K% at &0900

   * The ship line heap descending from WP at &0BE0

   * 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
     (only a portion of the LSO space station line heap is cleared)



.ZERO

Code variation 3 of 3Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

Cassette
Flight, Docked, 6502SP, Master
Electron
 LDX #&D                \ Point X to page &D

.ZEL

 JSR ZES1               \ Call ZES1 to zero-fill the page in X

 DEX                    \ Decrement X to point to the next page

 CPX #9                 \ If X is > 9 (i.e. is &A, &B or &C), then loop back
 BNE ZEL                \ up to clear the next page

                        \ Then fall through into ZES1 with X set to 9, so we
                        \ clear page &9 too
 LDX #(de-FRIN)         \ We're going to zero the UP 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

.ZEL2

 STA FRIN,X             \ Zero the X-th byte of FRIN to de

 DEX                    \ Decrement the loop counter

 BPL ZEL2               \ Loop back to zero the next variable until we have done
                        \ them all

 RTS                    \ Return from the subroutine
 LDX #&B                \ Point X to page &B

 JSR ZES1               \ Call ZES1 to zero-fill the page in X

 DEX                    \ Decrement X to point to the next page (&A)

 JSR ZES1               \ Call ZES1 to zero-fill the page in X

 DEX                    \ Decrement X to point to the next page

                        \ Then fall through into ZES1 with X set to 9, so we
                        \ clear page &9 too