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elite-loader.asm
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elite-loader.asm
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\ ******************************************************************************
\
\ ELECTRON ELITE LOADER SOURCE
\
\ Electron Elite was written by Ian Bell and David Braben and is copyright
\ Acornsoft 1984
\
\ The code on this site has been reconstructed from a disassembly of the version
\ released on Ian Bell's personal website at http://www.elitehomepage.org/
\
\ The commentary is copyright Mark Moxon, and any misunderstandings or mistakes
\ in the documentation are entirely my fault
\
\ The terminology and notations used in this commentary are explained at
\ https://elite.bbcelite.com/terminology
\
\ The deep dive articles referred to in this commentary can be found at
\ https://elite.bbcelite.com/deep_dives
\
\ ------------------------------------------------------------------------------
\
\ This source file produces the following binary file:
\
\ * ELITEDA.bin
\
\ ******************************************************************************
INCLUDE "1-source-files/main-sources/elite-build-options.asm"
_IB_SUPERIOR = (_VARIANT = 1)
_IB_ACORNSOFT = (_VARIANT = 2)
GUARD &5800 \ Guard against assembling over screen memory
\ ******************************************************************************
\
\ Configuration variables
\
\ ******************************************************************************
CODE% = &4400 \ The address where the code will be run
LOAD% = &4400 \ The address where the code will be loaded
DISC = TRUE \ Set to TRUE to load the code above DFS and relocate
\ down, so we can load the cassette version from disc
N% = 17 \ N% is set to the number of bytes in the VDU table, so
\ we can loop through them in part 2 below
USERV = &0200 \ The address of the user vector
BRKV = &0202 \ The address of the break vector
IRQ1V = &0204 \ The address of the interrupt vector
WRCHV = &020E \ The address of the write character vector
RDCHV = &0210 \ The address of the read character vector
KEYV = &0228 \ The address of the keyboard vector
LE% = &0B00 \ LE% is the address to which the code from UU% onwards
\ is copied in part 3
C% = &0D00 \ C% is set to the location that the main game code gets
\ moved to after it is loaded
L% = &2000 \ L% is the load address of the main game code file
S% = C% \ S% points to the entry point for the main game code
VIA = &FE00 \ Memory-mapped space for accessing internal hardware,
\ such as the video ULA, 6845 CRTC and 6522 VIAs (also
\ known as SHEILA)
OSWRCH = &FFEE \ The address for the OSWRCH routine
OSBYTE = &FFF4 \ The address for the OSBYTE routine
OSWORD = &FFF1 \ The address for the OSWORD routine
OSCLI = &FFF7 \ The address for the OSCLI routine
\ ******************************************************************************
\
\ Name: ZP
\ Type: Workspace
\ Address: &0004 to &0005 and &0070 to &0086
\ Category: Workspaces
\ Summary: Important variables used by the loader
\
\ ******************************************************************************
ORG &0004
.TRTB%
SKIP 2 \ Contains the address of the keyboard translation
\ table, which is used to translate internal key
\ numbers to ASCII
ORG &0070
.ZP
SKIP 2 \ Stores addresses used for moving content around
.P
SKIP 1 \ Temporary storage, used in a number of places
.Q
SKIP 1 \ Temporary storage, used in a number of places
.YY
SKIP 1 \ Temporary storage, used in a number of places
.T
SKIP 1 \ Temporary storage, used in a number of places
.SC
SKIP 1 \ Screen address (low byte)
\
\ Elite draws on-screen by poking bytes directly into
\ screen memory, and SC(1 0) is typically set to the
\ address of the character block containing the pixel
\ we want to draw (see the deep dives on "Drawing
\ monochrome pixels in mode 4" and "Drawing pixels
\ in the Electron version" for more details)
.SCH
SKIP 1 \ Screen address (high byte)
.BLPTR
SKIP 2 \ Gets set to &03CA as part of the obfuscation code
.V219
SKIP 2 \ Gets set to &0218 as part of the obfuscation code
SKIP 4 \ These bytes appear to be unused
.K3
SKIP 1 \ Temporary storage, used in a number of places
.BLCNT
SKIP 2 \ Stores the tape loader block count as part of the copy
\ protection code in IRQ1
.BLN
SKIP 2 \ Gets set to &03C6 as part of the obfuscation code
.EXCN
SKIP 2 \ Gets set to &03C2 as part of the obfuscation code
\ ******************************************************************************
\
\ ELITE LOADER
\
\ ******************************************************************************
ORG CODE%
\ ******************************************************************************
\
\ Name: Elite loader (Part 1 of 5)
\ Type: Subroutine
\ Category: Loader
\ Summary: Include binaries for recursive tokens and images
\
\ ------------------------------------------------------------------------------
\
\ The loader bundles a number of binary files in with the loader code, and moves
\ them to their correct memory locations in part 3 below.
\
\ There is one file containing code:
\
\ * WORDS9.bin contains the recursive token table, which is moved to &0400
\ before the main game is loaded
\
\ and four files containing images, which are all moved into screen memory by
\ the loader:
\
\ * P.A-SOFT.bin contains the "ACORNSOFT" title across the top of the loading
\ screen, which gets moved to screen address &5960, on the second character
\ row of the space view
\
\ * P.ELITE.bin contains the "ELITE" title across the top of the loading
\ screen, which gets moved to screen address &5B00, on the fourth character
\ row of the space view
\
\ * P.(C)ASFT.bin contains the "(C) Acornsoft 1984" title across the bottom
\ of the loading screen, which gets moved to screen address &73A0, the
\ penultimate character row of the space view, just above the dashboard
\
\ * P.DIALS.bin contains the dashboard, which gets moved to screen address
\ &7620, which is the starting point of the dashboard, just below the space
\ view
\
\ The routine ends with a jump to the start of the loader code at ENTRY.
\
\ ******************************************************************************
PRINT "WORDS9 = ",~P%
INCBIN "3-assembled-output/WORDS9.bin"
ALIGN 256
PRINT "P.DIALS = ",~P%
INCBIN "1-source-files/images/P.DIALS.bin"
PRINT "P.ELITE = ",~P%
INCBIN "1-source-files/images/P.ELITE.bin"
PRINT "P.A-SOFT = ",~P%
INCBIN "1-source-files/images/P.A-SOFT.bin"
PRINT "P.(C)ASFT = ",~P%
INCBIN "1-source-files/images/P.(C)ASFT.bin"
.run
JMP ENTRY \ Jump to ENTRY to start the loading process
\ ******************************************************************************
\
\ Name: B%
\ Type: Variable
\ Category: Drawing the screen
\ Summary: VDU commands for changing to a standard mode 4 screen
\
\ ------------------------------------------------------------------------------
\
\ This block contains the bytes that get written by OSWRCH to set up the screen
\ mode (this is equivalent to using the VDU statement in BASIC).
\
\ The Electron version of Elite is unique in that it uses a standard mode 4
\ screen, rather than the custom square mode used in the BBC versions. This is
\ because the Electron lacks the 6845 CRTC chip, which the BBC versions use to
\ customise the mode.
\
\ To make the Electron screen appear square like the BBC versions, there is a
\ blank 32-byte (&20-byte) margin on each end of each character row, so each
\ character row consists of 32 blank bytes on the left, then a page (256 bytes)
\ of screen memory containing the game display, then another 32 blank bytes on
\ the right. Screen memory is from &5800 to &7FFF, and the bottom row from &7EC0
\ to &7FFF is left blank, again to be consistent with look of the BBC version.
\ This means the screen takes up more memory on the Electron version than on the
\ BBC versions, despite showing the same amount of content.
\
\ On top of this, the Electron also lacks the Video ULA of the BBC Micro, so the
\ famous split-screen mode of the BBC versions can't be implemented in the
\ Electron version, as the BBC versions reprogram the ULA to create the coloured
\ dashboard. As a result, not only does the Electron suffer from the bigger
\ memory footprint of the screen, it also has to stick to the same palette for
\ the whole screen, so while the space view is the same monochrome mode 4 view
\ as in the BBC versions, the dashboard has to be in the same screen mode, so
\ it's also monochrome (though it has twice the number of horizontal pixels as
\ the four-colour mode 5 dashboard of the BBC versions, so it is noticeably
\ sharper, at least).
\
\ The following are also set up:
\
\ * The text window is 9 rows high and 15 columns wide, and is at (8, 10)
\
\ * The cursor is disabled
\
\ ******************************************************************************
.B%
EQUB 22, 4 \ Switch to screen mode 4
IF DISC
EQUB 28 \ Define a text window as follows:
EQUB 8, 19, 23, 10 \
\ * Left = 8
\ * Right = 23
\ * Top = 10
\ * Bottom = 19
\
\ i.e. 9 rows high, 15 columns wide at (8, 10)
ELSE
EQUB 28 \ Define a text window as follows:
EQUB 8, 23, 23, 14 \
\ * Left = 8
\ * Right = 23
\ * Top = 14
\ * Bottom = 23
\
\ i.e. 9 rows high, 15 columns wide at (8, 14)
\
\ This is slightly lower than the default window, as
\ otherwise the cassette's loading message overwrites
\ the main code file as it loads into screen memory
ENDIF
EQUB 23, 1, 0, 0 \ Disable the cursor
EQUB 0, 0, 0
EQUB 0, 0, 0
\ ******************************************************************************
\
\ Name: E%
\ Type: Variable
\ Category: Sound
\ Summary: Sound envelope definitions
\
\ ------------------------------------------------------------------------------
\
\ This table contains the sound envelope data, which is passed to OSWORD by the
\ FNE macro to create the four sound envelopes used in-game. Refer to chapter 22
\ of the Acorn Electron User Guide for details of sound envelopes and what all
\ the parameters mean.
\
\ The envelopes are as follows:
\
\ * Envelope 1 is the sound of our own laser firing
\
\ * Envelope 2 is the sound of lasers hitting us, or hyperspace
\
\ * Envelope 3 is the first sound in the two-part sound of us dying, or the
\ second sound in the two-part sound of us making hitting or killing an
\ enemy ship
\
\ * Envelope 4 is the sound of E.C.M. firing
\
\ ******************************************************************************
.E%
EQUB 1, 1, 0, 111, -8, 4, 1, 8, 126, 0, 0, -126, 126, 126
EQUB 2, 1, 14, -18, -1, 44, 32, 50, 6, 1, 0, -2, 120, 126
EQUB 3, 1, 1, -1, -3, 17, 32, 128, 1, 0, 0, -1, 1, 1
EQUB 4, 1, 4, -8, 44, 4, 6, 8, 22, 0, 0, -127, 126, 0
\ ******************************************************************************
\
\ Name: swine
\ Type: Subroutine
\ Category: Copy protection
\ Summary: Resets the machine if the copy protection detects a problem
\
\ ******************************************************************************
.swine
JMP (&FFFC) \ Jump to the address in &FFFC to reset the machine
\ ******************************************************************************
\
\ Name: OSB
\ Type: Subroutine
\ Category: Utility routines
\ Summary: A convenience routine for calling OSBYTE with Y = 0
\
\ ******************************************************************************
.OSB
LDY #0 \ Call OSBYTE with Y = 0, returning from the subroutine
JMP OSBYTE \ using a tail call (so we can call OSB to call OSBYTE
\ for when we know we want Y set to 0)
\ ******************************************************************************
\
\ Name: Authors' names
\ Type: Variable
\ Category: Copy protection
\ Summary: The authors' names, buried in the code
\
\ ------------------------------------------------------------------------------
\
\ Contains the authors' names, plus an unused OS command string that would
\ *RUN the main game code, which isn't what actually happens (so presumably
\ this is to throw the crackers off the scent).
\
\ ******************************************************************************
EQUS "RUN ELITEcode"
EQUB 13
EQUS "By D.Braben/I.Bell"
EQUB 13
EQUB &B0
\ ******************************************************************************
\
\ Name: oscliv
\ Type: Variable
\ Category: Utility routines
\ Summary: Contains the address of OSCLIV, for executing OS commands
\
\ ******************************************************************************
.oscliv
EQUW &FFF7 \ Address of OSCLIV, for executing OS commands
\ (specifically the *LOAD that loads the main game code)
\ ******************************************************************************
\
\ Name: David9
\ Type: Variable
\ Category: Copy protection
\ Summary: Address used as part of the stack-based decryption loop
\
\ ------------------------------------------------------------------------------
\
\ This address is used in the decryption loop starting at David2 in part 4, and
\ is used to jump back into the loop at David5.
\
\ ******************************************************************************
.David9
EQUW David5 \ The address of David5
CLD \ This instruction is not used
\ ******************************************************************************
\
\ Name: David23
\ Type: Variable
\ Category: Copy protection
\ Summary: Address pointer to the start of the 6502 stack
\
\ ------------------------------------------------------------------------------
\
\ This two-byte address points to the start of the 6502 stack, which descends
\ from the end of page 2, less LEN bytes, which comes out as &01DF. So when we
\ push 33 bytes onto the stack (LEN being 33), this address will point to the
\ start of those bytes, which means we can push executable code onto the stack
\ and run it by calling this address with a JMP (David23) instruction. Sneaky
\ stuff!
\
\ ******************************************************************************
.David23
EQUW 6 \ This value is not used in this unprotected version of
\ the loader, though why the crackers set it to 6 is a
\ mystery
\ ******************************************************************************
\
\ Name: doPROT1
\ Type: Subroutine
\ Category: Copy protection
\ Summary: Routine to self-modify the loader code
\
\ ------------------------------------------------------------------------------
\
\ This routine modifies various bits of code in-place as part of the copy
\ protection mechanism. It is called with A = &48 and X = 255.
\
\ ******************************************************************************
.doPROT1
LDY #&DB \ Store &EFDB in TRTB%(1 0) to point to the keyboard
STY TRTB% \ translation table for OS 0.1 (which we will overwrite
LDY #&EF \ with a call to OSBYTE later)
STY TRTB%+1
LDY #2 \ Set the high byte of V219(1 0) to 2
STY V219+1
CMP swine-5,X \ This part of the loader has been disabled by the
\ crackers, by changing an STA to a CMP (as this is an
\ unprotected version)
LDY #&18 \ Set the low byte of V219(1 0) to &18 (as X = 255), so
STY V219+1,X \ V219(1 0) now contains &0218
RTS \ Return from the subroutine
\ ******************************************************************************
\
\ Name: MHCA
\ Type: Variable
\ Category: Copy protection
\ Summary: Used to set one of the vectors in the copy protection code
\
\ ------------------------------------------------------------------------------
\
\ This value is used to set the low byte of BLPTR(1 0), when it's set in PLL1
\ as part of the copy protection.
\
\ ******************************************************************************
.MHCA
EQUB &CA \ The low byte of BLPTR(1 0)
\ ******************************************************************************
\
\ Name: David7
\ Type: Subroutine
\ Category: Copy protection
\ Summary: Part of the multi-jump obfuscation code in PROT1
\
\ ------------------------------------------------------------------------------
\
\ This instruction is part of the multi-jump obfuscation in PROT1 (see part 2 of
\ the loader), which does the following jumps:
\
\ David8 -> FRED1 -> David7 -> Ian1 -> David3
\
\ ******************************************************************************
.David7
BCC Ian1 \ This instruction is part of the multi-jump obfuscation
\ in PROT1
\ ******************************************************************************
\
\ Name: FNE
\ Type: Macro
\ Category: Sound
\ Summary: Macro definition for defining a sound envelope
\
\ ------------------------------------------------------------------------------
\
\ The following macro is used to define the four sound envelopes used in the
\ game. It uses OSWORD 8 to create an envelope using the 14 parameters in the
\ I%-th block of 14 bytes at location E%. This OSWORD call is the same as BBC
\ BASIC's ENVELOPE command.
\
\ See variable E% for more details of the envelopes themselves.
\
\ ******************************************************************************
MACRO FNE I%
LDX #LO(E%+I%*14) \ Set (Y X) to point to the I%-th set of envelope data
LDY #HI(E%+I%*14) \ in E%
LDA #8 \ Call OSWORD with A = 8 to set up sound envelope I%
JSR OSWORD
ENDMACRO
\ ******************************************************************************
\
\ Name: Elite loader (Part 2 of 5)
\ Type: Subroutine
\ Category: Loader
\ Summary: Perform a number of OS calls, set up sound, push routines on stack
\
\ ------------------------------------------------------------------------------
\
\ This part of the loader does a number of calls to OS routines, sets up the
\ sound envelopes, and pushes 33 bytes onto the stack. A lot of the code in this
\ routine has been removed or hobbled to remove the protection; for a full
\ picture of the protection that's missing, see the source code for the BBC
\ Micro cassette version, which contains almost exactly the same protection code
\ as the original Electron version.
\
\ ------------------------------------------------------------------------------
\
\ Other entry points:
\
\ Ian1 Re-entry point following the wild goose chase
\ obfuscation
\
\ ******************************************************************************
.ENTRY
NOP \ This part of the loader has been disabled by the
NOP \ crackers, as this is an unprotected version NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
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NOP
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NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
LDA #&60 \ This appears to be a lone instruction left over from
STA &0088 \ the unprotected code, as this value is never used
NOP \ This part of the loader has been disabled by the
NOP \ crackers, as this is an unprotected version
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
LDA #&20 \ Set A to the op code for a JSR call with absolute
\ addressing
NOP \ This part of the loader has been disabled by the
\ crackers, as this is an unprotected version
.Ian1
NOP \ This part of the loader has been disabled by the
NOP \ crackers, as this is an unprotected version
NOP
NOP
NOP
LSR A \ Set A = 16
LDX #3 \ Set the high bytes of BLPTR(1 0), BLN(1 0) and
STX BLPTR+1 \ EXCN(1 0) to &3. We will fill in the high bytes in
STX BLN+1 \ the PLL1 routine, and will then use these values in
STX EXCN+1 \ the IRQ1 handler
LDX #0 \ Call OSBYTE with A = 16 and X = 0 to set the joystick
LDY #0 \ port to sample 0 channels (i.e. disable it)
JSR OSBYTE
LDX #255 \ Call doPROT1 to change an instruction in the PROT1
LDA #&95 \ routine and set up another couple of variables
JSR doPROT1
LDA #144 \ Call OSBYTE with A = 144, X = 255 and Y = 0 to move
JSR OSB \ the screen down one line and turn screen interlace on
EQUB &2C \ Skip the next instruction by turning it into
\ &2C &D0 &92, or BIT &92D0, which does nothing apart
\ from affect the flags
.FRED1
BNE David7 \ This instruction is skipped if we came from above,
\ otherwise this is part of the multi-jump obfuscation
\ in PROT1
LDA #247 \ Call OSBYTE with A = 247 and X = Y = 0 to disable the
LDX #0 \ BREAK intercept code by poking 0 into the first value
JSR OSB
LDA #143 \ Call OSBYTE 143 to issue a paged ROM service call of
LDX #&C \ type &C with argument &FF, which is the "NMI claim"
LDY #&FF \ service call that asks the current user of the NMI
JSR OSBYTE \ space to clear it out
LDA #13 \ Set A = 13 for the next OSBYTE call
.abrk
LDX #0 \ Call OSBYTE with A = 13, X = 0 and Y = 0 to disable
JSR OSB \ the "output buffer empty" event
LDA #225 \ Call OSBYTE with A = 225, X = 128 and Y = 0 to set
LDX #128 \ the function keys to return ASCII codes for SHIFT-fn
JSR OSB \ keys (i.e. add 128)
LDA #172 \ Call OSBYTE 172 to read the address of the MOS
LDX #0 \ keyboard translation table into (Y X)
LDY #255
JSR OSBYTE
STX TRTB% \ Store the address of the keyboard translation table in
STY TRTB%+1 \ TRTB%(1 0)
NOP \ This part of the loader has been disabled by the
NOP \ crackers, as this is an unprotected version
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
LDA #13 \ Call OSBYTE with A = 13, X = 2 and Y = 0 to disable
LDX #2 \ the "character entering keyboard buffer" event
JSR OSB
.OS01
LDX #&FF \ Set the stack pointer to &01FF, which is the standard
TXS \ location for the 6502 stack, so this instruction
\ effectively resets the stack
INX \ Set X = 0, to use as a counter in the following loop
\ The following loop copies the crunchit routine into
\ zero page, though this unprotected version of the
\ loader doesn't call it there, so this has no effect
LDY #0 \ Set a counter in Y for the copy
.David3
LDA crunchit,Y \ Copy the Y-th byte of crunchit
.PROT1
STA TRTB%+2,X \ And store it in the X-th byte of zero page after the
\ TRTB%(1 0) variable
INX \ Increment both byte counters
INY
CPY #33 \ Loop back to copy the next byte until we have copied
BNE David3 \ all 33 bytes
LDA #LO(B%) \ Set the low byte of ZP(1 0) to point to the VDU code
STA ZP \ table at B%
LDA #&95 \ This part of the loader has been disabled by the
BIT PROT1 \ crackers, as this is an unprotected version (the BIT
\ instruction is an STA instruction in the full version,
\ but it has been hobbled here)
LDA #HI(B%) \ Set the high byte of ZP(1 0) to point to the VDU code
STA ZP+1 \ table at B%
LDY #0 \ We are now going to send the N% VDU bytes in the table
\ at B% to OSWRCH to set up the screen mode
.LOOP
LDA (ZP),Y \ Pass the Y-th byte of the B% table to OSWRCH
JSR OSWRCH
INY \ Increment the loop counter
CPY #N% \ Loop back for the next byte until we have done them
BNE LOOP \ all (the number of bytes was set in N% above)
LDA #1 \ This part of the loader has been disabled by the
TAX \ crackers, as this is an unprotected version (the CMP
TAY \ instruction is an STA instruction in the full version,
LDA abrk+1 \ but it has been hobbled here)
CMP (V219),Y
LDA #4 \ Call OSBYTE with A = 4, X = 1 and Y = 0 to disable
JSR OSB \ cursor editing, so the cursor keys return ASCII values
\ and can therefore be used in-game
LDA #9 \ Call OSBYTE with A = 9, X = 0 and Y = 0 to disable
LDX #0 \ flashing colours
JSR OSB
LDA #&6C \ This part of the loader has been disabled by the
NOP \ crackers, as this is an unprotected version (the BIT
NOP \ instruction is an STA instruction in the full version,
NOP \ but it has been hobbled here)
BIT &544F
FNE 0 \ Set up sound envelopes 0-3 using the FNE macro
FNE 1
FNE 2
FNE 3
\ ******************************************************************************
\
\ Name: Elite loader (Part 3 of 5)
\ Type: Subroutine
\ Category: Loader
\ Summary: Move recursive tokens and images
\
\ ------------------------------------------------------------------------------
\
\ Move the following memory blocks:
\
\ * WORDS9: move 4 pages (1024 bytes) from &4400 (CODE%) to &0400
\
\ * P.ELITE: move 1 page (256 bytes) from &4F00 (CODE% + &0B00) to &5BE0
\
\ * P.A-SOFT: move 1 page (256 bytes) from &5000 (CODE% + &0C00) to &5960
\
\ * P.(C)ASFT: move 1 page (256 bytes) from &5100 (CODE% + &0D00) to &73A0
\
\ * P.DIALS: move 7 pages (1792 bytes) from &4800 (CODE% + &0400) to &7620
\
\ * Move 1 page (256 bytes) from &5615 (UU%) to &0B00-&0BFF
\
\ and call the routine to draw Saturn between P.(C)ASFT and P.DIALS.
\
\ The dashboard image (P.DIALS) is moved into screen memory one page at a time,
\ but not in a contiguous manner - it has to take into account the &20 bytes of
\ blank margin at each edge of the screen (see the description of the screen
\ mode in B% above). So the seven rows of the dashboard are actually moved into
\ screen memory like this:
\
\ 1 page from &4800 to &7620 = &7620
\ 1 page from &4900 to &7720 + &40 = &7760
\ 1 page from &4A00 to &7820 + 2 * &40 = &78A0
\ 1 page from &4B00 to &7920 + 3 * &40 = &79E0
\ 1 page from &4C00 to &7A20 + 4 * &40 = &7B20
\ 1 page from &4D00 to &7B20 + 5 * &40 = &7C60
\ 1 page from &4E00 to &7C20 + 6 * &40 = &7DA0
\
\ See part 1 above for more details on the above files and the locations that
\ they are moved to.
\
\ The code at UU% (see below) forms part of the loader code and is moved before
\ being run, so it's tucked away safely while the main game code is loaded and
\ decrypted.
\
\ In the unprotected version of the loader, the images are encrypted and this
\ part also decrypts them, but this is an unprotected version of the game, so
\ the encryption part of the crunchit routine is disabled.
\
\ ******************************************************************************
LDX #4 \ Set the following:
STX P+1 \
LDA #HI(CODE%) \ P(1 0) = &0400
STA ZP+1 \ ZP(1 0) = CODE%
LDY #0 \ (X Y) = &400 = 1024
LDA #256-232 \
CMP (V219-4,X) \ The CMP instruction is an STA instruction in the
STY ZP \ protected version of the loader, but this version has
STY P \ been hacked to remove the protection, and the crackers
\ just switched the STA to a CMP to disable this bit of
\ the protection code
JSR crunchit \ Call crunchit to move &400 bytes from CODE% to &0400.
\ We loaded WORDS9.bin to CODE% in part 1, so this moves
\ WORDS9
LDX #1 \ Set the following:
LDA #(HI(CODE%)+&B) \
STA ZP+1 \ P(1 0) = &5BE0
LDA #&5B \ ZP(1 0) = CODE% + &B
STA P+1 \ (X Y) = &100 = 256
LDA #&E0
STA P
LDY #0
JSR crunchit \ Call crunchit to move &100 bytes from CODE% + &B to
\ &5BE0, so this moves P.ELITE
LDX #1 \ Set the following:
LDA #(HI(CODE%)+&C) \
STA ZP+1 \ P(1 0) = &5960
LDA #&59 \ ZP(1 0) = CODE% + &C
STA P+1 \ (X Y) = &100 = 256
LDA #&60
STA P
LDY #0
JSR crunchit \ Call crunchit to move &100 bytes from CODE% + &C to
\ &5960, so this moves P.A-SOFT
LDX #1 \ Set the following:
LDA #(HI(CODE%)+&D) \
STA ZP+1 \ P(1 0) = &73A0
LDA #&73 \ ZP(1 0) = CODE% + &D
STA P+1 \ (X Y) = &100 = 256
LDA #&A0
STA P
LDY #0
JSR crunchit \ Call crunchit to move &100 bytes from CODE% + &D to
\ &73A0, so this moves P.(C)ASFT
JSR PLL1 \ Call PLL1 to draw Saturn
LDA #(HI(CODE%)+4) \ Set the following:
STA ZP+1 \
LDA #&76 \ P(1 0) = &7620
STA P+1 \ ZP(1 0) = CODE% + &4
LDY #0 \ Y = 0
STY ZP \
LDX #&20 \ Also set BLCNT = 0
STY BLCNT
STX P
.dialsL
LDX #1 \ Set (X Y) = &100 = 256
JSR crunchit \ Call crunchit to move &100 bytes from ZP(1 0) to
\ P(1 0), so this moves P.DIALS one row at a time
CLC \ Set P(1 0) = P(1 0) + &40 to skip the screen margins
LDA P
ADC #&40
STA P
LDA P+1
ADC #0
STA P+1
CMP #&7E \ Loop back to copy the next row of the dashboard until
BCC dialsL \ we have poked the last one into screen memory
LDX #1 \ Set the following:
LDA #HI(UU%) \
STA ZP+1 \ P(1 0) = LE%
LDA #LO(UU%) \ ZP(1 0) = UU%
STA ZP \ (X Y) = &100 = 256
LDA #HI(LE%)
STA P+1
LDY #0
STY P
JSR crunchit \ Call crunchit to move &100 bytes from UU% to LE%
\ ******************************************************************************
\
\ Name: Elite loader (Part 4 of 5)
\ Type: Subroutine
\ Category: Loader
\ Summary: Call part 5 of the loader now that is has been relocated
\
\ ------------------------------------------------------------------------------
\
\ In the protected version of the loader, this part copies more code onto the
\ stack and decrypts a chunk of loader code before calling part 5, but in the
\ unprotected version it's mostly NOPs.
\
\ ******************************************************************************
JMP &0B11 \ Call relocated UU% routine to load the main game code
\ at &2000, move it down to &0D00 and run it
NOP \ This part of the loader has been disabled by the
NOP \ crackers, as this is an unprotected version
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP