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Adds title screen section to tutorial #83

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47 changes: 47 additions & 0 deletions unbricked/title-screen/input.asm
Original file line number Diff line number Diff line change
@@ -0,0 +1,47 @@
; This is a simplified version of pads.z80 by PinoBatch for use in gb-asm-tutorial
; All labels are intentionally not exported to avoid confusing the reader with unfamiliar syntax.
; Once linking is introduced in part 3, a new, exported version of this file will be provided.
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maybe we can open an issue regarding exporting labels in a later interaction?


INCLUDE "../hardware.inc"

SECTION "Input Variables", WRAM0
wCurKeys:: db
wNewKeys:: db

SECTION "UpdateKeys", ROM0

UpdateKeys::
; Poll half the controller
ld a, P1F_GET_BTN
call .onenibble
ld b, a ; B7-4 = 1; B3-0 = unpressed buttons

; Poll the other half
ld a, P1F_GET_DPAD
call .onenibble
swap a ; A3-0 = unpressed directions; A7-4 = 1
xor a, b ; A = pressed buttons + directions
ld b, a ; B = pressed buttons + directions

; And release the controller
ld a, P1F_GET_NONE
ldh [rP1], a

; Combine with previous wCurKeys to make wNewKeys
ld a, [wCurKeys]
xor a, b ; A = keys that changed state
and a, b ; A = keys that changed to pressed
ld [wNewKeys], a
ld a, b
ld [wCurKeys], a
ret

.onenibble
ldh [rP1], a ; switch the key matrix
call .knownret ; burn 10 cycles calling a known ret
ldh a, [rP1] ; ignore value while waiting for the key matrix to settle
ldh a, [rP1]
ldh a, [rP1] ; this read counts
or a, $F0 ; A7-4 = 1; A3-0 = unpressed keys
.knownret
ret
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