Routines
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52500: Game Entry Point
Manually write "JP Handler_Interrupts" at AliasInterruptRedirect.
GameEntryPoint 52500 LD HL,65278 HL=AliasInterruptRedirect.
52503 LD A,195 Write 195 which is the opcode for the "JP" instruction to *HL.
52505 LD (HL),A
52506 INC HL Increment HL by one.
52507 LD A,105 Write 105 to *HL.
52509 LD (HL),A
52510 INC HL Increment HL by one.
52511 LD A,254 Write 254 to *HL.
52513 LD (HL),A
All will become clear soon...
52514 LD HL,62464 Write 254 to 0260 bytes, starting from InterruptLowOrderByteJumpTable.
52517 LD BC,260
WriteInterruptJumpAddress 52520 LD A,254
52522 LD (HL),A
52523 INC HL
52524 DEC BC
52525 LD A,B
52526 OR C
52527 JR NZ,WriteInterruptJumpAddress
52529 LD BC,0 Write 0000 to:
52532 LD (65534),BC
52536 LD (65532),BC
52540 LD (65531),BC
52544 DI Disable interrupts.
52545 LD HL,64000 Write MelodyData_ThemeTune to *MusicPointerThemeMusic.
52548 LD (65529),HL
This sets interrupt mode 2; when the system generates an interrupt, it'll use the high-order byte set here, together with a low-order byte generated from the system to form a 16-bit address to jump to.
As we've just set 254 to every address, this means that every generated interrupt will jump to AliasInterruptRedirect, which in turn will jump to Handler_Interrupts.
52551 LD A,244 Set 244 as the high-order byte in I.
52553 LD I,A
52555 IM 2 Set interrupt mode 2.
52557 LD A,3 Write 3 to:
52559 LD (65527),A
52562 LD (65528),A
52565 EI Enable interrupts.
52566 LD HL,41068 HL=Graphics_MaskSprite.
52569 LD B,128 B=128.
52571 XOR A Write 0 to *HL.
GameEntryPoint_0 52572 LD (HL),A
52573 INC HL Increment HL by one.
52574 DJNZ GameEntryPoint_0 Decrease counter by one and loop back to GameEntryPoint_0 until counter is zero.
52576 EXX Switch to the shadow registers.
52577 PUSH HL Stash HL' on the stack.
52578 EXX Switch back to the normal registers.
52579 XOR A Write 0 to *DF_SZ.
52580 LD (23659),A
52583 LD A,2 A=2.
52585 CALL 5633 Call CHAN_OPEN.
52588 JP DisplayIntroductionScreen Jump to DisplayIntroductionScreen.
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