90 lines
1.8 KiB
NASM
90 lines
1.8 KiB
NASM
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; Handle the serial link cable
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#IF HARDWARE_LINK
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; FF> = Idle
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; D6> = Read: D0><[L] D1><[H] [HL]>
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; D9> = Write: D8><[L] D9><[H] DA><[^DATA] DB><[DATA]
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; DD> = OrW: D8><[L] D9><[H] DA><[^DATA] DB><[DATA] (used to set flags without requiring a slow read,modify,write race condition)
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handleSerialLink:
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; Check if we got a byte from hardware
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ldh a, [$01]
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cp $D6
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jr z, serialReadMem
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cp $D9
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jr z, serialWriteMem
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cp $DD
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jr z, serialOrMem
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finishSerialLink:
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; Do a new idle transfer.
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ld a, $E4
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ldh [$01], a
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ld a, $81
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ldh [$02], a
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ret
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serialReadMem:
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ld a, $D0
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call serialTransfer
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ld h, a
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ld a, $D1
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call serialTransfer
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ld l, a
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ld a, [hl]
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call serialTransfer
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jr finishSerialLink
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serialWriteMem:
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ld a, $D8
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call serialTransfer
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ld h, a
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ld a, $D9
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call serialTransfer
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ld l, a
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ld a, $DA
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call serialTransfer
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cpl
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ld c, a
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ld a, $DB
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call serialTransfer
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cp c
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jr nz, finishSerialLink
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ld [hl], a
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jr finishSerialLink
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serialOrMem:
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ld a, $D8
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call serialTransfer
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ld h, a
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ld a, $D9
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call serialTransfer
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ld l, a
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ld a, $DA
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call serialTransfer
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cpl
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ld c, a
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ld a, $DB
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call serialTransfer
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cp c
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jr nz, finishSerialLink
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ld c, a
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ld a, [hl]
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or c
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ld [hl], a
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jr finishSerialLink
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; Transfer A to the serial link and wait for it to be done and return the result in A
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serialTransfer:
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ldh [$01], a
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ld a, $81
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ldh [$02], a
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.loop:
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ldh a, [$02]
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and $80
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jr nz, .loop
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ldh a, [$01]
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ret
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#ENDIF
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