The SVE subroutine - Elite on the BBC Micro

       Name: SVE                                                     [Show more]
       Type: Subroutine
   Category: Save and load
    Summary: Display the disc access menu and process saving of commander files
  Deep dive: Commander save files
             The competition code
    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * BR1 (Part 1 of 2) calls SVE
             * BRBR calls SVE
             * DELT calls SVE
             * LOD calls SVE
             * TT102 calls SVE


.SVE

 TSX                    \ Transfer the stack pointer to X and store it in stack,
 STX stack              \ so we can restore it in the BRBR routine

 JSR TRADE              \ Set the palette for trading screens and switch the
                        \ current colour to white

 LDA #1                 \ Print extended token 1, the disc access menu, which
 JSR DETOK              \ presents these options:
                        \
                        \   1. Load New Commander
                        \   2. Save Commander {commander name}
                        \   3. Catalogue
                        \   4. Delete A File
                        \   5. Default JAMESON
                        \   6. Exit

 JSR t                  \ Scan the keyboard until a key is pressed, returning
                        \ the ASCII code in A and X

 CMP #'1'               \ Option 1 was chosen, so jump to LD1 to load a new
 BEQ LD1                \ commander

 CMP #'2'               \ Option 2 was chosen, so jump to SV1 to save the
 BEQ SV1                \ current commander

 CMP #'3'               \ Option 3 was chosen, so jump to CAT to catalogue a
 BEQ CAT                \ disc

 CMP #'4'               \ If option 4 wasn't chosen, skip the next two
 BNE P%+8               \ instructions

 JSR DELT               \ Option 4 was chosen, so call DELT to delete a file

 JMP SVE                \ Jump to SVE to display the disc access menu again and
                        \ return from the subroutine using a tail call

 CMP #'5'               \ If option 5 wasn't chosen, skip to exit to exit the
 BNE exit               \ menu

 LDA #224               \ Print extended token 224 ("ARE YOU SURE?")
 JSR DETOK

 JSR GETYN              \ Call GETYN to wait until either "Y" or "N" is pressed

 BCC exit               \ If "N" was pressed, jump to exit

 JSR JAMESON            \ Otherwise "Y" was pressed, so call JAMESON to set the
                        \ last saved commander to the default "JAMESON"
                        \ commander

 JMP DFAULT             \ Jump to DFAULT to reset the current commander data
                        \ block to the last saved commander, returning from the
                        \ subroutine using a tail call

.exit

 CLC                    \ Option 5 was chosen, so clear the C flag to indicate
                        \ that nothing was loaded

 RTS                    \ Return from the subroutine

.CAT

 JSR CATS               \ Call CATS to ask for a drive number (or a directory
                        \ name on the Master Compact) and catalogue that disc
                        \ or directory

 JSR t                  \ Scan the keyboard until a key is pressed, returning
                        \ the ASCII code in A and X

 JMP SVE                \ Jump to SVE to display the disc access menu and return
                        \ from the subroutine using a tail call

.LD1

 JSR GTNMEW             \ If we get here then option 1 (load) was chosen, so
                        \ call GTNMEW to fetch the name of the commander file
                        \ to load (including drive number and directory) into
                        \ INWK

IF _SNG47

 JSR GTDRV              \ Get an ASCII disc drive drive number from the keyboard
                        \ in A, setting the C flag if an invalid drive number
                        \ was entered

 BCS LDdone             \ If the C flag is set, then an invalid drive number was
                        \ entered, so return from the subroutine (as DELT-1
                        \ contains an RTS)

 STA LDLI+6             \ Store the ASCII drive number in LDLI+6, which is the
                        \ drive character of the load filename string ":1.E."

ENDIF

 JSR LOD                \ Call LOD to load the commander file

 JSR TRNME              \ Transfer the commander filename from INWK to NA%

 SEC                    \ Set the C flag to indicate we loaded a new commander

.LDdone

 RTS                    \ Return from the subroutine

.SV1

 JSR GTNMEW             \ If we get here then option 2 (save) was chosen, so
                        \ call GTNMEW to fetch the name of the commander file
                        \ to save (including drive number and directory) into
                        \ INWK

 JSR TRNME              \ Transfer the commander filename from INWK to NA%

 LSR SVC                \ Halve the save count value in SVC

 LDA #4                 \ Print extended token 4, which is blank (this was where
 JSR DETOK              \ the competition number was printed in older versions,
                        \ but the competition was long gone by the time of the
                        \ BBC Master version

 LDX #NT%               \ We now want to copy the current commander data block
                        \ from location TP to the last saved commander block at
                        \ NA%+8, so set a counter in X to copy the NT% bytes in
                        \ the commander data block

.SVL1

 LDA TP,X               \ Copy the X-th byte of TP to the X-th byte of NA%+8
 STA NA%+8,X

 DEX                    \ Decrement the loop counter

 BPL SVL1               \ Loop back until we have copied all the bytes in the
                        \ commander data block

 JSR CHECK              \ Call CHECK to calculate the checksum for the last
                        \ saved commander and return it in A

 STA CHK                \ Store the checksum in CHK, which is at the end of the
                        \ last saved commander block

 PHA                    \ Store the checksum on the stack

 ORA #%10000000         \ Set K = checksum with bit 7 set
 STA K

 EOR COK                \ Set K+2 = K EOR COK (the competition flags)
 STA K+2

 EOR CASH+2             \ Set K+1 = K+2 EOR CASH+2 (the third cash byte)
 STA K+1

 EOR #&5A               \ Set K+3 = K+1 EOR &5A EOR TALLY+1 (the high byte of
 EOR TALLY+1            \ the kill tally)
 STA K+3

 CLC                    \ Clear the C flag so the call to BPRNT does not include
                        \ a decimal point

 JSR TT67               \ Call TT67 twice to print two newlines
 JSR TT67

 PLA                    \ Restore the checksum from the stack

 EOR #&A9               \ Store the checksum EOR &A9 in CHK2, the penultimate
 STA CHK2               \ byte of the last saved commander block

 LDY #NT%               \ We now want to copy the current commander data block
                        \ to location &0791 so we can do a file save operation,
                        \ so set a counter in X to copy the NT% bytes in the
                        \ commander data block

.SVL2

 LDA NA%+8,Y            \ Copy the X-th byte of NA% to the X-th byte of &0791
 STA &0791,Y

 DEY                    \ Decrement the loop counter

 BPL SVL2               \ Loop back until we have copied all the bytes in the
                        \ commander data block

IF _SNG47

 JSR GTDRV              \ Get an ASCII disc drive drive number from the keyboard
                        \ in A, setting the C flag if an invalid drive number
                        \ was entered

 BCS P%+8               \ If the C flag is set, then an invalid drive number was
                        \ entered, so skip the next two instructions

 STA SVLI+6             \ Store the ASCII drive number in SVLI+6, which is the
                        \ drive character of the save filename string ":1.E."

ENDIF

 JSR SAVE               \ Call SAVE to save the commander file

 JSR DFAULT             \ Call DFAULT to reset the current commander data
                        \ block to the last saved commander

 CLC                    \ Clear the C flag to indicate that no new commander
                        \ file was loaded

 RTS                    \ Return from the subroutine

[X]

Variable CASH in workspace WP

Our current cash pot

[X]

Label CAT is local to this routine

[X]

Subroutine CATS (category: Save and load)

Ask for a disc drive number and print a catalogue of that drive

[X]

Subroutine CHECK (category: Save and load)

Calculate the checksum for the last saved commander data block

[X]

Variable CHK (category: Save and load)

First checksum byte for the saved commander data file

[X]

Variable CHK2 (category: Save and load)

Second checksum byte for the saved commander data file

[X]

Variable COK in workspace WP

Flags used to generate the competition code

[X]

Subroutine DELT (category: Save and load)

Catalogue a disc, ask for a filename to delete, and delete the file

[X]

Subroutine DETOK (category: Text)

Print an extended recursive token from the TKN1 token table

[X]

Subroutine GETYN (category: Keyboard)

Wait until either "Y" or "N" is pressed

[X]

Subroutine GTDRV (category: Save and load)

Get an ASCII disc drive drive number from the keyboard

[X]

Subroutine GTNMEW (category: Save and load)

Fetch the name of a commander file to save or load

[X]

Subroutine JAMESON (category: Save and load)

Restore the default JAMESON commander

[X]

Variable K in workspace ZP

Temporary storage, used in a number of places

[X]

Label LD1 is local to this routine

[X]

Variable LDLI (category: Save and load)

The OS command string for loading a commander file

[X]

Label LDdone is local to this routine

[X]

Subroutine LOD (category: Save and load)

Load a commander file

[X]

Variable NA% (category: Save and load)

The data block for the last saved commander

[X]
Configuration variable: NT% = SVC + 3 - TP
This sets the variable NT% to the size of the current commander data block, which starts at TP and ends at SVC+3 (inclusive), i.e. with the last checksum byte

[X]

Subroutine SAVE (category: Save and load)

Save the commander file

[X]

Label SV1 is local to this routine

[X]

Variable SVC in workspace WP

The save count

[X]

Subroutine SVE (category: Save and load)

Display the disc access menu and process saving of commander files

[X]

Label SVL1 is local to this routine

[X]

Label SVL2 is local to this routine

[X]

Variable SVLI (category: Save and load)

The OS command string for saving a commander file

[X]

Variable TALLY in workspace WP

Our combat rank

[X]

Variable TP in workspace WP

The current mission status

[X]

Entry point TRADE in subroutine TRADEMODE (category: Utility routines)

Set the palette for trading screens and switch the current colour to white

[X]

Subroutine TRNME (category: Save and load)

Copy the last saved commander's name from INWK to NA%

[X]

Subroutine TT67 (category: Text)

Print a newline

[X]

Label exit is local to this routine

[X]

Variable stack (category: Save and load)

Temporary storage for the stack pointer when jumping to the break handler at BRBR

[X]

Entry point t in subroutine TT217 (category: Keyboard)

As TT217 but don't preserve Y, set it to YSAV instead