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SystemRoutines.asm
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; ================================================================
; System routines
; ================================================================
; ================================================================
; Clear work RAM
; ================================================================
ClearWRAM:
ld hl,$c000
ld bc,$2000
jr ClearLoop ; routine continues in ClearLoop
; ================================================================
; Clear tilemap area
; ================================================================
ClearScreen:
ld hl,$9800
ld bc,$7ff
jr ClearLoop ; routine continues in ClearLoop
; ================================================================
; Clear video RAM
; ================================================================
ClearVRAM:
ld hl,$8000
ld bc,$1fff
; fall through to ClearLoop
; ================================================================
; Clear a section of RAM
; ================================================================
ClearLoop:
xor a
ld [hl+],a
dec bc
ld a,b
or c
jr nz,ClearLoop
ret
; ================================================================
; Wait for LCD status to change
; ================================================================
WaitStat:
.a ld a,[rSTAT]
and 2
jr z,.a
.b ld a,[rSTAT]
and 2
jr nz,.b
ret
; ================================================================
; Check joypad input
; ================================================================
CheckInput:
ld a,P1F_5
ld [rP1],a
ld a,[rP1]
ld a,[rP1]
cpl
and $f
swap a
ld b,a
ld a,P1F_4
ld [rP1],a
ld a,[rP1]
ld a,[rP1]
ld a,[rP1]
ld a,[rP1]
ld a,[rP1]
ld a,[rP1]
cpl
and a,$f
or a,b
ld b,a
ld a,[sys_btnHold]
xor b
and b
ld [sys_btnPress],a
ld a,b
ld [sys_btnHold],a
ld a,P1F_5|P1F_4
ld [rP1],a
ret
; ================================================================
; Draw hexadecimal number A at HL
; ================================================================
DrawHex:
push af
swap a
call .loop1
pop af
.loop1
and $f
cp $a
jr c,.loop2
add a,$7
.loop2
add a,$10
ld [hl+],a
ret
; ================================================================
; Switch between single and double speed mode
; ================================================================
DoubleSpeed:
ldh a,[rKEY1]
bit 7,a ; already in double speed?
ret nz ; if yes, return
; jr DoSpeedSwitch
;NormalSpeed:
; ldh a,[rKEY1]
; bit 7,a ; already normal speed
; ret z ; if yes, return
; fall through
DoSpeedSwitch:
ld a,%00110000
ldh [rP1],a
xor %00110001 ; a = %00000000
ldh [rKEY1],a ; prepare speed switch
stop
ret