100 lines
2.0 KiB
NASM
100 lines
2.0 KiB
NASM
; DMGTRIS
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; Copyright (C) 2023 - Randy Thiemann <randy.thiemann@gmail.com>
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; This program is free software: you can redistribute it and/or modify
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; it under the terms of the GNU General Public License as published by
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; the Free Software Foundation, either version 3 of the License, or
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; (at your option) any later version.
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; This program is distributed in the hope that it will be useful,
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; but WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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; GNU General Public License for more details.
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; You should have received a copy of the GNU General Public License
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; along with this program. If not, see <https://www.gnu.org/licenses/>.
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IF !DEF(INTERRUPTS_ASM)
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DEF INTERRUPTS_ASM EQU 1
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INCLUDE "globals.asm"
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DEF INIT_SCY EQU 3
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DEF INIT_LYC EQU 3
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SECTION "High Interrupt Variables", HRAM
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hLCDCCtr:: ds 1
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SECTION "Interrupt Initialization Functions", ROM0
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EnableScreenSquish::
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di
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nop
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xor a, a
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ldh [hLCDCCtr], a
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ld a, STATF_LYC
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ldh [rSTAT], a
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ld a, INIT_LYC
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ldh [rLYC], a
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ld a, INIT_SCY
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ldh [rSCY], a
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ld a, IEF_STAT
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ldh [rIE], a
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xor a, a
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ldh [rIF], a
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ei
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ret
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DisableScreenSquish::
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di
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nop
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xor a, a
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ldh [rIE], a
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ldh [rIF], a
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ldh [rSCY], a
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ei
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ret
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SECTION "LCDC Interrupt", ROM0[INT_HANDLER_STAT]
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; This interrupt handler will be called every 7 scanlines, scrolling up the tile map by 1 line. This has the
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; effect of making the tiles appear as 8x7 pixels, and making 20 rows fit on the screen.
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LCDCInterrupt:
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push af
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push hl
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ld hl, rSTAT
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LCDCInterrupt_WaitUntilNotBusy:
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bit STATB_BUSY, [hl]
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jr nz, LCDCInterrupt_WaitUntilNotBusy
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; Increment SCY
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ldh a, [rSCY]
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inc a
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ldh [rSCY], a
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; Increment LYC by 7
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ldh a, [rLYC]
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add a, 7
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ldh [rLYC], a
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; Check our interrupt counter
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cp a, 144
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jr c, LCDCInterrupt_End
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ld a, INIT_LYC
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ldh [rLYC], a
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ld a, INIT_SCY
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ldh [rSCY], a
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LCDCInterrupt_End:
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pop hl
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pop af
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reti
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ENDC
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