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BBC Micro Elite

Loader: Elite loader (Part 3 of 6)

Name: Elite loader (Part 3 of 6) [View in context] Type: Subroutine Category: Loader Summary: Move and decrypt recursive tokens, Python blueprint and images
Move and decrypt the following memory blocks: * WORDS9: move 4 pages (1024 bytes) from CODE% to &0400 * P.ELITE: move 1 page (256 bytes) from CODE% + &C00 to &6300 * P.A-SOFT: move 1 page (256 bytes) from CODE% + &D00 to &6100 * P.(C)ASFT: move 1 page (256 bytes) from CODE% + &E00 to &7600 * P.DIALS and PYTHON: move 8 pages (2048 bytes) from CODE% + &400 to &7800 * Move 2 pages (512 bytes) from UU% to &0B00-&0CFF and call the routine to draw Saturn between P.(C)ASFT and P.DIALS. 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.
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-LEN1 \ STA (V219-4,X) \ In doPROT1 above we set V219(1 0) = &0218, so this STY ZP \ also sets the contents of &0218 (the low byte of STY P \ BPUTV) to 256 - LEN1, or &F1. We set the low byte to \ 1 above, so BPUTV now contains &01F1, which we will \ use at the start of part 4 JSR crunchit \ Call crunchit, which has now been modified to call the \ MVDL routine on the stack, to move and decrypt &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%)+&C) \ STA ZP+1 \ P(1 0) = &6300 LDA #&63 \ ZP(1 0) = CODE% + &C STA P+1 \ (X Y) = &100 = 256 LDY #0 JSR crunchit \ Call crunchit to move and decrypt &100 bytes from \ CODE% + &C to &6300, so this moves P.ELITE LDX #1 \ Set the following: LDA #(HI(CODE%)+&D) \ STA ZP+1 \ P(1 0) = &6100 LDA #&61 \ ZP(1 0) = CODE% + &D STA P+1 \ (X Y) = &100 = 256 LDY #0 JSR crunchit \ Call crunchit to move and decrypt &100 bytes from \ CODE% + &D to &6100, so this moves P.A-SOFT LDX #1 \ Set the following: LDA #(HI(CODE%)+&E) \ STA ZP+1 \ P(1 0) = &7600 LDA #&76 \ ZP(1 0) = CODE% + &E STA P+1 \ (X Y) = &100 = 256 LDY #0 JSR crunchit \ Call crunchit to move and decrypt &100 bytes from \ CODE% + &E to &7600, so this moves P.(C)ASFT JSR PLL1 \ Call PLL1 to draw Saturn LDX #8 \ Set the following: LDA #(HI(CODE%)+4) \ STA ZP+1 \ P(1 0) = &7800 LDA #&78 \ ZP(1 0) = CODE% + &4 STA P+1 \ (X Y) = &800 = 2048 LDY #0 \ STY ZP \ Also set BLCNT = 0 STY BLCNT STY P JSR crunchit \ Call crunchit to move and decrypt &800 bytes from \ CODE% + &4 to &7800, so this moves P.DIALS and PYTHON LDX #(3-(DISC AND 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) = &300 = 768 (if we are building for tape) LDA #HI(LE%) \ or &200 = 512 (if we are building for disc) STA P+1 LDY #0 STY P JSR crunchit \ Call crunchit to move and decrypt either &200 or &300 \ bytes from UU% to LE%, leaving X = 0