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Elite on the BBC Micro

Loader: Elite loader (Part 3 of 5) [Electron version, Loader]

Name: Elite loader (Part 3 of 5) [Show more] Type: Subroutine Category: Loader Summary: Move recursive tokens and images
Context: See this subroutine in context in the source code References: No direct references to this subroutine in this source file

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%