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Elite on the BBC Micro

Loader 2 source (Disc version)

DISC ELITE LOADER (PART 2) SOURCE Elite was written by Ian Bell and David Braben and is copyright Acornsoft 1984 The code on this site has been disassembled from 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://www.bbcelite.com/about_site/terminology_used_in_this_commentary.html The deep dive articles referred to in this commentary can be found at https://www.bbcelite.com/deep_dives
This source file produces the following binary file: * output/ELITE3.bin
INCLUDE "sources/elite-header.h.asm" _IB_DISC = (_RELEASE = 1) _STH_DISC = (_RELEASE = 2) OSNEWL = &FFE7 \ The address for the OSNEWL routine 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 vector VIA = &FE00 \ Memory-mapped space for accessing internal hardware, \ such as the video ULA, 6845 CRTC and 6522 VIAs (also \ known as SHEILA) CODE% = &5700 LOAD% = &5700
Name: ZP [View individually] Type: Workspace Address: &0004 to &0005 and &0070 to &0082 Category: Workspaces Summary: Important variables used by the loader
ORG &0004 .TRTB% SKIP 2 \ TRTB%(1 0) points to the keyboard translation table, \ which is used to translate internal key numbers to \ ASCII ORG &0070 .S SKIP 1 \ Temporary storage, used in a number of places .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 .R SKIP 1 \ Temporary storage, used in a number of places .T SKIP 1 \ Temporary storage, used in a number of places ORG &0081 .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 colour \ pixels in mode 5" for more details) .SCH SKIP 1 \ Screen address (high byte)
ELITE LOADER
ORG CODE%
Name: Elite loader (Part 1 of 4) [View individually] Type: Subroutine Category: Loader Summary: Various copy protection checks, plus make sure there is no Tube
.ENTRY LDA #0 \ We start by deleting the first loader from memory, so \ it doesn't leave any clues for the crackers, so set A \ to 0 so we can zero the memory TAY \ Set Y to 0 to act as an index in the following loop .LOOP1 STA &2F00,Y \ Zero the Y-th byte of &2F00, which is where the first \ loader was running before it loaded this one INY \ Increment the loop counter BNE LOOP1 \ Loop back until we have zeroed all 256 bytes from \ &2F00 to &2FFF, leaving Y = 0 LDA #0 \ Set &3FFF = 0 STA &3FFF LDA #64 \ Set &7FFF = 64 STA &7FFF EOR &3FFF \ Set A = 64 EOR &3FFF \ = 64 EOR 0 \ = 64 CLC \ Set A = A + 64 ADC #64 \ = 64 + 64 \ = 128 PHA \ Push 128 on the stack TAX \ Set X = 128 LDA #254 \ Call OSBYTE with A = 254, X = 128 and Y = 0 to set LDY #0 \ the available RAM to 32K JSR OSBYTE PLA \ Pull 128 from the stack into A AND &5973 \ &5973 contains 128, so set A = 128 AND 128 = 128 IF _REMOVE_CHECKSUMS NOP \ If we have disabled checksums, ignore the result in A NOP ELSE BEQ P% \ If A = 0 then enter an infinite loop, which hangs the \ computer ENDIF JSR PROT1 \ Call PROT1 to display the mode 7 loading screen and \ perform lots of copy protection LDA #172 \ Call OSBYTE 172 to read the address of the MOS LDX #0 \ keyboard translation table into (Y X) LDY #&FF JSR OSBYTE STX TRTB% \ Store the address of the keyboard translation table in STY TRTB%+1 \ TRTB%(1 0) LDA #234 \ Call OSBYTE with A = 234, X = 0 and Y = &FF, which LDX #0 \ detects whether Tube hardware is present, returning LDY #&FF \ X = 0 (not present) or X = &FF (present) JSR OSBYTE CPX #&FF \ If X is not &FF, i.e. we are not running this over the BNE notube \ Tube, then jump to notube LDA &5A00 \ &5A00 contains 0, so set A = 0 BEQ P% \ If A = 0 then enter an infinite loop, which hangs the \ computer JMP &5A00 \ Otherwise we jump to &5A00, though I have no idea why, \ as we will only get here if the code has been altered \ in some way .notube LDA MPL \ Set A = &A0, as MPL contains an LDY #0 instruction NOP \ These bytes appear to be unused NOP NOP JMP MPL \ Jump to MPL to copy 512 bytes to &0400 and jump to \ ENTRY2 SKIP 8 \ These bytes appear to be unused NOP NOP
Name: Elite loader (Part 2 of 4) [View individually] Type: Subroutine Category: Loader Summary: Jump straight to part 3, as the copy protection code has been removed
.ENTRY2 JMP ENTRY3 \ Jump to the next part, as the copy protection code has \ been removed NOP \ These bytes appear to be unused NOP NOP NOP
Name: Elite loader (Part 4 of 4) [View individually] Type: Subroutine Category: Loader Summary: Load and run the ELITE4 loader
.ENTRY4 LDX #LO(MESS1) \ Set (Y X) to point to MESS1 ("LOAD Elite4") LDY #HI(MESS1) JSR OSCLI \ Call OSCLI to run the OS command in MESS1, which loads \ the ELITE4 binary to its load address of &1900 LDA #21 \ Call OSBYTE with A = 21 and X = 0 to flush the LDX #0 \ keyboard buffer JSR OSBYTE LDA #201 \ Call OSBYTE with A = 201, X = 1 and Y = 1 to re-enable LDX #1 \ the keyboard, which we disabled in the first loader LDY #1 JSR OSBYTE JMP &197B \ Jump to the start of the ELITE4 loader code at &197B SKIP 15 \ These bytes appear to be unused
Name: MESS1 [View individually] Type: Variable Category: Loader Summary: The OS command string for loading the ELITE4 loader
.MESS1 EQUS "LOAD Elite4" EQUB 13 SKIP 4 \ These bytes appear to be unused
Name: Elite loader (Part 3 of 4) [View individually] Type: Subroutine Category: Loader Summary: Pause for a surprisingly long time (7.67 seconds) so people can enjoy the Acornsoft loading screen
.ENTRY3 LDA #129 \ Call OSBYTE with A = 129, X = &FF and Y = 2 to scan LDY #2 \ the keyboard for &2FF centiseconds (7.67 seconds) LDX #&FF JSR OSBYTE LDA #15 \ Call OSBYTE with A = 129 and Y = 0 to flush the input LDY #0 \ buffer JSR OSBYTE JMP ENTRY4 \ Jump to ENTRY4 to load and run the next part of the \ loader SKIP 63 \ These bytes appear to be unused EQUB &32 SKIP 13
Name: MPL [View individually] Type: Subroutine Category: Utility routines Summary: Move two pages of memory from LOADcode to LOAD and jump to ENTRY2
.MPL LDY #0 \ Set Y = 0 to act as a byte counter LDX #2 \ Set X = 2 to act as a page counter .MVBL LDA LOADcode,Y \ Copy the Y-th byte of LOADcode to the Y-th byte of STA LOAD,Y \ LOAD (this instruction gets modified below, so this is \ a single-use, self-modifying routine) INY \ Increment the byte counter BNE MVBL \ Loop back to MVBL to copy the next byte until we have \ copied a whole page INC MVBL+2 \ Increment the high byte of the LDA instruction above, \ so it now points to the next page INC MVBL+5 \ Increment the high byte of the STA instruction above, \ so it now points to the next page DEX \ Decrement the page counter in X BNE MVBL \ Loop back to MVBL to copy the next page until we have \ copied X pages JMP ENTRY2 \ Jump to ENTRY2 to continue the loading process
Name: LOADcode [View individually] Type: Subroutine Category: Copy protection Summary: LOAD routine, bundled up in the loader so it can be moved to &0400 to be run
.LOADcode ORG &0400
Name: LOAD [View individually] Type: Subroutine Category: Copy protection Summary: This code accesses the disc directly (not used in this version as disc protection is disabled)
.LOAD JSR LOAD10 PLA STA L0509 PLA STA L050A PLA CLC ADC L0551 STA L0557 PLA STA L0559 PLA STA L0558 BEQ LOAD2 .LOAD1 JSR LOAD7 DEC L0558 BNE LOAD1 .LOAD2 LDA L0559 BEQ LOAD3 ORA #&20 STA L0511 JSR LOAD7 .LOAD3 LDA L051A BEQ LOAD5 LDY #&00 .LOAD4 LDA &0700,Y STA &1000,Y INY BNE LOAD4 .LOAD5 LDX L055B BEQ LOAD6 LDX #&52 LDY #&05 JSR OSCLI LDX #&02 .LOAD6 STX &76 \ Store the drive number in &76 for retrieval in ELITE4 LDA #&15 LDX #&00 JSR OSBYTE LDA #&C9 LDX #&01 LDY #&01 JMP OSBYTE .LOAD7 JSR LOAD11 LDA #&28 SEC SBC L0557 STA L0545 STA L050F LDA #&01 JSR LOAD13 LDA L050A CMP #&0E BNE LOAD8 LDA L050F STA L051A STA L0525 STA L0530 LDA #&04 JSR LOAD13 LDA #&05 JSR LOAD13 LDA #&06 JSR LOAD13 JMP LOAD9 .LOAD8 LDA #&03 JSR LOAD13 .LOAD9 LDA L053B STA L0545 LDA #&01 JSR LOAD13 LDA L050A CLC ADC #&0A STA L050A INC L0557 RTS .LOAD10 JSR LOAD11 LDA L053B STA L054E LDA #&02 JSR LOAD13 RTS .LOAD11 LDA L0557 LDX L055B BEQ LOAD12 ASL A .LOAD12 STA L053B LDA #&00 .LOAD13 STA R .LOAD14 LDA R ASL A TAX LDA L04FA,X LDY L04FA+1,X TAX STX P STY P+1 LDA #127 JSR OSWORD LDA R CMP #&03 BCC LOAD15 LDY #&0A LDA (P),Y AND #&DF BNE LOAD14 .LOAD15 RTS .L04FA EQUB &34 EQUB &05, &3D, &05, &47, &05, &08, &05, &13 EQUB &05, &1E, &05, &29, &05, &FF .L0509 EQUB &00 .L050A EQUB &0A EQUB &FF, &FF, &03, &57 .L050F EQUB &00, &F6 .L0511 EQUB &2A, &00 EQUB &FF, &00, &0E, &FF, &FF, &03, &57 .L051A EQUB &00 EQUB &F6, &22, &00, &FF, &00, &07, &FF, &FF EQUB &03, &57 .L0525 EQUB &00, &F8, &21, &00, &FF, &00 EQUB &11, &FF, &FF, &03, &57 .L0530 EQUB &00, &F9, &27 EQUB &00, &FF, &FF, &FF, &FF, &FF, &01, &69 .L053B EQUB &00, &00, &FF, &FF, &FF, &FF, &FF, &02 EQUB &7A, &12 .L0545 EQUB &00, &00, &FF, &00, &07, &FF EQUB &FF, &03, &5B .L054E EQUB &00, &00, &0A .L0551 EQUB &00, &44 EQUB &52, &2E, &32, &0D .L0557 EQUB &03 .L0558 EQUB &00 .L0559 EQUB &00 EQUB &80 \ This is location &5973, as referenced by part 1 .L055B EQUB &FF, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00 \ This is location &5A00, as referenced by part 1 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &00, &00 COPYBLOCK LOAD, P%, LOADcode ORG LOADcode + P% - LOAD SKIP 487 \ These bytes appear to be unused
Name: ECHAR [View individually] Type: Variable Category: Loader Summary: Character definitions for the Electron to mimic the graphics characters of the BBC Micro's mode 7 teletext screen
.ECHAR EQUB &00, &00, &00, &00, &00, &00, &00, &00 EQUB &E0, &E0, &00, &00, &00, &00, &00, &00 EQUB &0E, &0E, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &0E, &0E EQUB &E0, &E0, &00, &E0, &E0, &00, &00, &00 EQUB &EE, &EE, &00, &E0, &E0, &00, &00, &00 EQUB &EE, &EE, &00, &0E, &0E, &00, &00, &00 EQUB &00, &00, &00, &00, &00, &00, &E0, &E0 EQUB &E0, &E0, &00, &00, &00, &00, &E0, &E0 EQUB &00, &00, &00, &E0, &E0, &00, &E0, &E0 EQUB &E0, &E0, &00, &E0, &E0, &00, &E0, &E0 EQUB &EE, &EE, &00, &E0, &E0, &00, &E0, &E0 EQUB &EE, &EE, &00, &EE, &EE, &00, &E0, &E0 EQUB &EE, &EE, &00, &00, &00, &00, &00, &00 EQUB &00, &00, &00, &0E, &0E, &00, &0E, &0E EQUB &0E, &0E, &00, &0E, &0E, &00, &0E, &0E EQUB &EE, &EE, &00, &0E, &0E, &00, &0E, &0E EQUB &EE, &EE, &00, &EE, &EE, &00, &0E, &0E EQUB &00, &00, &00, &00, &00, &00, &EE, &EE EQUB &EE, &EE, &00, &00, &00, &00, &EE, &EE EQUB &00, &00, &00, &E0, &E0, &00, &EE, &EE EQUB &E0, &E0, &00, &E0, &E0, &00, &EE, &EE EQUB &00, &00, &00, &0E, &0E, &00, &EE, &EE EQUB &0E, &0E, &00, &0E, &0E, &00, &EE, &EE EQUB &00, &00, &00, &EE, &EE, &00, &EE, &EE EQUB &E0, &E0, &00, &EE, &EE, &00, &EE, &EE EQUB &0E, &0E, &00, &EE, &EE, &00, &EE, &EE EQUB &EE, &EE, &00, &EE, &EE, &00, &EE, &EE
Name: LOGO [View individually] Type: Variable Category: Loader Summary: Tables containing the Acornsoft logo for the BBC Micro and Acorn Electron
.LOGO EQUB &A0, &A1 \ For the BBC Micro, the tables below consist of offsets EQUB &A2, &E0 \ into this top table, so the first three characters of EQUB &A5, &A7 \ the Acornsoft logo are &A0 (the &00-th entry in this EQUB &AB, &B0 \ table), then &FC (the &18-th entry in this table), EQUB &B1, &B4 \ then &B4 (the &09-th entry in this table) and so on EQUB &B5, &B7 \ EQUB &BF, &A3 \ The Electron ignores this top table and just uses the EQUB &E8, &EA \ values below, adding &E0 to get the number of the EQUB &EB, &EF \ relevant user-defined character (so the first three EQUB &F0, &F3 \ characters are &E0, then &F8, then &E9 and so on) EQUB &F4, &F5 \ EQUB &F8, &FA \ The Acornsoft logo is made up of 5 rows with 38 EQUB &FC, &FD \ graphics characters on each row, which corresponds EQUB &FE, &FF \ with the tables below EQUB &00, &00, &00, &18, &09, &03, &18, &18 EQUB &07, &00, &16, &18, &14, &00, &18, &18 EQUB &18, &07, &0E, &14, &00, &0E, &09, &16 EQUB &18, &18, &07, &00, &1A, &1B, &09, &00 EQUB &18, &18, &18, &18, &18, &18 EQUB &00, &00, &17, &1B, &0A, &1B, &05, &06 EQUB &1B, &0F, &0C, &0D, &11, &0A, &1B, &0D EQUB &10, &0A, &0F, &1B, &09, &0F, &0A, &1B EQUB &08, &06, &04, &0F, &1B, &1B, &1B, &00 EQUB &1B, &0D, &0D, &0D, &1B, &0D EQUB &00, &0E, &0C, &10, &0A, &1B, &00, &00 EQUB &00, &0F, &0A, &00, &0F, &0A, &1B, &18 EQUB &1A, &04, &0F, &0C, &1B, &17, &0A, &06 EQUB &1B, &19, &07, &1B, &1B, &1B, &1B, &0A EQUB &1B, &1B, &1B, &00, &1B, &00 EQUB &03, &1B, &19, &1A, &0A, &1B, &07, &03 EQUB &18, &0F, &15, &00, &17, &0A, &1B, &06 EQUB &19, &00, &0F, &0A, &10, &1B, &0A, &12 EQUB &00, &10, &1B, &13, &13, &13, &13, &08 EQUB &1B, &00, &00, &00, &1B, &00 EQUB &1A, &0B, &00, &0F, &0A, &06, &1B, &1B EQUB &05, &02, &11, &1B, &0C, &01, &1B, &00 EQUB &10, &15, &0F, &0A, &00, &11, &0A, &11 EQUB &1B, &1B, &04, &11, &1B, &1B, &1B, &04 EQUB &1B, &00, &00, &00, &1B, &00 SKIP 28 \ These bytes appear to be unused EQUB &02, &0D SKIP 8
Name: PROT1 [View individually] Type: Subroutine Category: Loader Summary: Various copy protection shenanigans in preparation for showing the Acornspft loading screen
.PROT1 LDA #&68 \ Poke the following routine into &0100 to &0108: STA &0100 \ STA &0103 \ 0100 : &68 PLA LDA #&85 \ 0101 : &85 &71 STA ZP STA &0101 \ 0103 : &68 PLA STA &0104 \ 0104 : &85 &72 STA ZP+1 LDX #&71 \ 0106 : &6C &71 &00 JMP (ZP) STX &0107 \ STX &0102 \ This routine pulls an address off the stack into a INX \ location in zero page, and then jumps to that address STX &0105 LDA #&6C STA &0106 LDA #&00 STA &0108 .do JSR &0100 \ Call the subroutine at &0100, which does the EQUB 0 \ following: \ \ * The JSR puts the address of the last byte of the \ JSR instruction on the stack (i.e. the address of \ the &01), pushing the high byte first \ \ * It then jumps to &0100, which pulls the address \ off the stack and puts it in ZP(1 0) \ \ * The final instruction of the routine at &0100 \ jumps to the address in ZP(1 0), i.e. it jumps to \ the &01 of the JSR instruction. The &01 byte is \ followed by a &00 byte, and &01 &00 is the opcode \ for ORA (&00,X), which doesn't do anything apart \ from affect the value of the accumulator \ \ In other words, this whole routine is a complicated \ way of pointing ZP(1 0) to the &01 byte in the JSR \ instruction above, i.e. to do + 2 LDA ZP \ Set ZP(1 0) = ZP(1 0) - (2 + do - PROT1) SEC \ = do + 2 - 2 - do + PROT1 SBC #(2 + do - PROT1) \ = PROT1 STA ZP LDA ZP+1 SBC #&00 STA ZP+1 LDY #(TABLE - PROT1) \ We're now going to loop through the words in TABLE, so \ set Y as an index we can add to PROT1 (i.e. ZP) to \ reach TABLE .PROT1a LDA (ZP),Y \ Set SC(1 0) = ZP(1 0) + Y-th word from TABLE CLC \ ADC ZP \ so, for example, the first entry in TABLE does this: STA SC \ INY \ SC(1 0) = ZP + first word from TABLE LDA (ZP),Y \ = PROT1 + jsr1 + 1 - PROT1 ADC ZP+1 \ = jsr1 + 1 STA SC+1 \ \ which is the address of the destination adress in the \ JSR instruction at jsr1 LDX #0 \ Add ZP(1 0), i.e. PROT1, to the word at SC(1 0), LDA (SC,X) \ starting with the low bytes CLC ADC ZP STA (SC,X) INC SC \ And then adding the high bytes BNE P%+4 \ INC SC+1 \ So, for example, the first entry in TABLE modifies the LDA (SC,X) \ destination address of the JSR at jsr1 by adding PROT1 ADC ZP+1 \ to it, so the address now points to prstr STA (SC,X) INY \ Increment Y to point to the next word in TABLE CPY #&7D \ Loop until we have done them all BNE PROT1a BEQ LOADSCR \ Jump to LOADSCR (this BEQ is effectively a JMP as we \ didn't take the BNE branch) .TABLE EQUW jsr1 + 1 - PROT1 \ Offsets within PROT1 of JSR destination addresses that EQUW jsr2 + 1 - PROT1 \ we modify with the code above EQUW jsr3 + 1 - PROT1 EQUW jsr4 + 1 - PROT1 EQUW jsr5 + 1 - PROT1 EQUW jsr6 + 1 - PROT1 SKIP 14 \ These bytes appear to be unused
Name: LOADSCR [View individually] Type: Subroutine Category: Loader Summary: Show the mode 7 Acornsoft loading screen
.LOADSCR LDA ZP \ Set ZP(1 0) = ZP(1 0) - (PROT1 - ECHAR) SEC \ = PROT1 - PROT1 + ECHAR SBC #LO(PROT1 - ECHAR) \ = ECHAR STA ZP LDA ZP+1 SBC #HI(PROT1 - ECHAR) STA ZP+1 LDX #0 \ Set S = 0, to use as a flag denoting whether this is a STX S \ BBC Micro (0) or an Electron (&FF) LDY #&FF \ Call OSBYTE with A = 129, X = 0 and Y = &FF to detect LDA #129 \ the machine type. This call is undocumented and is not JSR OSBYTE \ the recommended way to determine the machine type \ (OSBYTE 0 is the correct way), but this call returns \ the following: \ \ * X = Y = 0 if this is a BBC Micro with MOS 0.1 \ * X = Y = 1 if this is an Electron \ * X = Y = &FF if this is a BBC Micro with MOS 1.20 CPX #1 \ If X is not 1, then this is not an Electron, so jump BNE bbc \ to bbc DEC S \ Decrement S to &FF, to denote that this is an Acorn \ Electron \ We now define a character set consisting of "fake" \ mode 7 graphics characters so the Electron can print \ its own version of the Acornsoft loading screen \ despite not having the BBC Micro's teletext mode 7 \ \ The comand to define a character is as follows: \ \ VDU 23, n, b0, b1, b2, b3, b4, b5, b6, b7 \ \ where n is the character number and b0 through b7 are \ the bytes for each pixel row in the character (there \ are 8 rows of 8 pixels in a character) \ \ So in the following, we perform the above command \ for each character using the values from the ECHAR \ table LDY #0 \ Set Y to act as an index into the table at ECHAR .eloop LDX #7 \ Set a counter in X for the 8 bytes we need to print \ from the table for each character definition (one byte \ per pixel row) LDA #23 \ Print character 23 (i.e. VDU 23) JSR OSWRCH TYA \ We will increase Y by 8 for each character, so this LSR A \ sets A = Y / 8 to give the character number, starting LSR A \ from 0 and counting up by 1 for each new character LSR A ORA #&E0 \ This adds &E0 to A, so our new character set starts \ with character number &E0, then character number &E1, \ and so on JSR OSWRCH \ Print the character number (so we have now done the \ VDU 23, n part of the command) .vloop LDA (ZP),Y \ Print the Y-th byte from the ECHAR table (we set ZP to JSR OSWRCH \ point to ECHAR above) INY \ Increment the index to point to the next byte in the \ table DEX \ Decrement the byte counter BPL vloop \ Loop back until we have printed 8 characters CPY #224 \ Loop back to do the next VDU 23 command until we have BNE eloop \ printed out the whole table .bbc \ We now print the Acornsoft loading screen background \ using mode 7 graphics (for the BBC Micro) or the \ "fake" characters we just defined (for the Electron \ version) LDA ZP \ Set ZP(1 0) = ZP(1 0) + LOGO - ECHAR CLC \ = ECHAR + LOGO - ECHAR ADC #(LOGO - ECHAR) \ = LOGO STA ZP BCC P%+4 INC ZP+1 LDA #22 \ Switch to mode 7 using a VDU 22, 7 command JSR OSWRCH LDA #7 JSR OSWRCH .jsr1 JSR prstr - PROT1 \ Call prstr to print the following characters, \ restarting from the NOP instruction (this destination \ address is modified by the code above that adds PROT1 \ to the address) EQUB 23, 0, 10, 32 \ Set 6845 register R10 = 32 EQUB 0, 0, 0 \ EQUB 0, 0, 0 \ This is the "cursor start" register, which sets the \ cursor start line at 0, so it turns the cursor off NOP \ Marks the end of the VDU block LDA #145 \ Set T to teletext control code 145 (Red graphics) to STA T \ specify that the first Acornsoft is red .jsr2 JSR jsr5 - PROT1 \ Call jsr5, which calls jsr6, which calls LOGOS (this \ destination address is modified by the code above that \ adds PROT1 to the address) BIT S \ If bit 7 of S is set (this is an Electron), jump to BMI jsr4 \ jsr4 .jsr3 \ If we get here then this is a BBC Micro, so we can \ show the game's name in the mode 7 screen JSR prstr - PROT1 \ Call prstr to print the following characters, \ restarting from the NOP instruction (this destination \ address is modified by the code above that adds PROT1 \ to the address) EQUB 28 \ Define a text window as follows: EQUB 13, 13, 25, 10 \ \ * Left = 13 \ * Right = 25 \ * Top = 10 \ * Bottom = 13 \ \ i.e. 3 rows high, 12 columns wide at (13, 10) EQUB 12 \ Clear the text area EQUB 10 \ Move the cursor down one row EQUB 135 \ Teletext control code 135 (Select white text) EQUB 141 \ Teletext control code 141 (Double height) EQUS "E L I T E" \ The top half of the game's name EQUB 140 \ Teletext control code 140 (Turn off double height) EQUB 146 \ Teletext control code 146 (Select green graphics) EQUB 135 \ Teletext control code 135 (Select white text) EQUB 141 \ Teletext control code 141 (Double height) EQUS "E L I T E" \ The top half of the game's name NOP \ Marks the end of the VDU block RTS \ Return from the PROT1 subroutine EQUS " " \ These bytes appear to be unused EQUB 140, 146 EQUB 135, 141 EQUS " " EQUS " " EQUS " " EQUS " " EQUS " " NOP RTS .jsr4 \ If we get here then this is an Electron JSR prstr - PROT1 \ Call prstr to print the following characters, \ restarting from the NOP instruction (this destination \ address is modified by the code above that adds PROT1 \ to the address) EQUB 28 \ Define a text window as follows: EQUB 13, 12, 25, 10 \ \ * Left = 13 \ * Right = 25 \ * Top = 10 \ * Bottom = 12 \ \ i.e. 2 rows high, 12 columns wide at (13, 10) EQUB 12 \ Clear the text area EQUB 26 \ Restore default windows EQUB 31, 15, 11 \ Move text cursor to 15, 11 EQUS "E L I T E" \ The name of the game NOP \ Marks the end of the VDU block RTS \ Return from the PROT1 subroutine EQUS " " \ These bytes appear to be unused EQUS " " NOP RTS .jsr5 JSR jsr6 - PROT1 \ Call jsr6 (this destination address is modified by the \ code above that adds PROT1 to the address). This calls \ the LOGOS routine twice to print two Acornsoft logos, \ with a newline between then JSR OSNEWL \ Print two newlines JSR OSNEWL .jsr6 JSR LOGOS - PROT1 \ Call LOGOS (this destination address is modified by \ the code above that adds PROT1 to the address). This \ prints a third Acornsoft logo JSR OSNEWL \ Print a newline \ Fall through into LOGOS to print a fourth Acornsoft \ logo and return from the subroutine using a tail call
Name: LOGOS [View individually] Type: Subroutine Category: Loader Summary: Print a large Acornsoft logo as part of the loading screen
Arguments: T The logo colour as a teletext control code for graphics colour ZP(1 0) The address of the Acornsoft logo character table at LOGO
.LOGOS LDY #28 \ Set Y = 28 as an index to the first row of logo \ characters in the table at LOGO, after the 28 bytes of \ lookup data in the first part of the table .aloop LDX #38 \ Each row of the Acornsoft logo consists of 38 teletext \ graphics characters, so set a counter in X to count \ through the characters BIT S \ If bit 7 of S is set (this is an Electron), jump to BMI eskip1 \ eskip1 to skip the teletext colour codes (as the \ Electron loading screen is monochrome) LDA T \ Print the character in T, which starts with teletext JSR OSWRCH \ control code 145 (Red graphics) and increments through \ the colours, so this sets the correct colour for the \ current Acornsoft logo LDA #154 \ Print teletext control code 154 (Separated graphics) JSR OSWRCH CLC \ Skip the next two instructions BCC P%+7 .eskip1 LDA #' ' \ Print a space (on the Electron only) JSR OSWRCH .cloop LDA (ZP),Y \ Fetch the Y-th character from ZP into A, so A contains \ the next byte from LOGO, which is the user-defined \ character we want to print (in the case of the \ Electron), or the index into the first section of the \ LOGO table for the teletext graphics character we want \ to print (in the case of the BBC Micro) BIT S \ If bit 7 of S is set (this is an Electron), jump to BMI eskip2 \ eskip2 STY P \ Store Y so we can retrieve it below TAY \ This is a BBC Micro, so the number in A is the index LDA (ZP),Y \ into the first section of the LOGO table for the \ teletext graphics character we want to print, so we \ now fetch that character LDY P \ Retrieve the value of Y we stored above BNE P%+4 \ Skip the next instruction (this BNE is effectively a \ JMP as Y is never zero) .eskip2 ORA #&E0 \ Add &E0 to the character number (on the Electron only) JSR OSWRCH \ Print the character in A INY \ Increment Y to point to the next byte in the table CPY #255 \ If Y = 255 then we are done printing all 5 rows of the BEQ adone \ logo, so jump to adone to finish off DEX \ Otherwise decrement the character counter in X BNE cloop \ Loop back to print the next character until we have \ done all 38 in this row BIT S \ If bit 7 of S is clear (this is a BBC Micro), skip the BPL P%+7 \ next two instructions LDA #' ' \ Print a space (on the Electron only) JSR OSWRCH CLC \ Jump back to aloop to print the next row in the logo BCC aloop .adone INC T \ Increment the colour in T, which started with teletext \ control code 145 (Red graphics) and increments through \ 146 (green), 147 (yellow) and 148 (blue) with each new \ call to the LOGOS routine RTS \ Return from the subroutine
Name: prstr [View individually] Type: Subroutine Category: Loader Summary: Print the NOP-terminated string immediately following the JSR instruction that called the routine
.prstr PLA \ We call prstr with a JSR, so pull the return address STA Q \ off the stack into Q(1 0), which actually points to PLA \ the last byte of the JSR prstr instruction STA Q+1 .p1 INC Q \ Increment Q(1 0) to point to the next byte (so the BNE P%+4 \ first time we call prstr, Q points to the first byte INC Q+1 \ of the string we want to print) LDY #0 \ Fetch the byte at Q(1 0) into A LDA (Q),Y CMP #&EA \ If we just fetched a NOP instruction (opcode &EA), BEQ p2 \ then we have reached the end of the string, so jump to \ p2 to return from the subroutine JSR OSWRCH \ Print the byte we just fetched CLC \ Loop back to p1 to fetch the next byte to print BCC p1 .p2 JMP (Q) \ Jump to the address in Q(1 0) - i.e. to the NOP that \ we just fetched, so execution continues from the end \ of the string we just printed
Name: Unused copy protection routine [View individually] Type: Subroutine Category: Copy protection Summary: This code doesn't appear to be run in this version
SKIP 76 \ These bytes appear to be unused EQUB &FF SKIP 255 BNE LABEL1 LDA &50 CMP &4E .LABEL1 BNE LABEL2 LDA #&00 STA &4E LDA #&00 STA &4F JMP &4953 .LABEL2 BIT &495C BPL LABEL3 RTS .LABEL3 LDA &4F BNE LABEL4 JSR &4BBA .LABEL4 LDA &4D BNE LABEL5 JSR &4BC3 LDA #&00 STA &4E LDA #&00 STA &4F JMP &4953 .LABEL5 LDA &4D CMP &4F BCC LABEL6 BNE LABEL6 LDA &4C CMP &4E .LABEL6 BCC LABEL7 LDA &4C STA &12 LDA &4D STA &13 JSR &4BC3 LDA &12 STA &4E LDA &13 STA &4F .LABEL7 BIT &495C BMI LABEL8 JSR &373D .LABEL8 RTS SKIP 1 .LABEL9 LDA &4F BEQ LABEL11 LDA &4F CMP &51 BCC LABEL10 BNE LABEL10 LDA &4E CMP &50 .LABEL10 BCS LABEL11 JMP &49D6 .LABEL11 LDA &4D BEQ LABEL13 LDA &4D CMP &51 BCC LABEL12 BNE LABEL12 LDA &4C CMP &50 .LABEL12 BCS LABEL13 JMP &499C .LABEL13 RTS LDA &4D BEQ LABEL18 LDA &4D CMP &51 BCC LABEL14 BNE LABEL14 LDA &4C CMP &50 .LABEL14 BEQ LABEL18 BCC LABEL18 BIT &0AC1 BEQ LABEL17 LDA &4F CMP &51 BCC LABEL15 BNE LABEL15 LDA &4E CMP &50 .LABEL15 BEQ LABEL16 LDA &50 STA &4C LDA &51 STA &4D JSR &373D .LABEL16 RTS .LABEL17 JSR &4BCC JSR &373D RTS .LABEL18 LDA &4F BEQ LABEL23 LDA &4F CMP &51 BCC LABEL19 BNE LABEL19 LDA &4E CMP &50 .LABEL19 BEQ LABEL23 BCC LABEL23 BIT &0AC1 BEQ LABEL22 LDA &4D CMP &51 BCC LABEL20 BNE LABEL20 LDA &4C CMP &50 .LABEL20 BEQ LABEL21 JSR &4BBA JSR &373D .LABEL21 RTS .LABEL22 LDA &4E STA &50 LDA &4F STA &51 JSR &373D .LABEL23 RTS LDA &44 STA &4C
Save output/ELITE2.bin
PRINT "S.ELITE3 ", ~CODE%, " ", ~P%, " ", ~LOAD%, " ", ~LOAD% SAVE "output/ELITE3.bin", CODE%, P%, LOAD%