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44 lines
861 B
44 lines
861 B
include "sdk/hardware.inc"
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SECTION "gbsdk_sgb_functions", ROM0
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_sgb_send::
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pop de
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pop hl
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; hl=pointer to data to send
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; SGB RESET pulse
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xor a
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ldh [rP1], a
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push hl ; done here for delay reasons
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cpl
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ldh [rP1], a
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push de ; done here for delay reasons
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ld e, 16 ; amount of bytes to send
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.byteLoop:
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ld a, [hl+]
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ld d, a ; byte to send in d
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ld c, 8 ; amount of bits to send
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.bitLoop:
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bit 0, d
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ld a, P1F_5
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jr z, .zero
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ld a, P1F_4
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.zero:
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ldh [rP1], a
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rr d ; 2cycles
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ld a, P1F_5 | P1F_4 ; 2cycles
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dec c ; 1cycle
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ldh [rP1], a
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jr nz, .bitLoop
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dec e
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jr nz, .byteLoop
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ld a, P1F_5
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ldh [rP1], a
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ldh [rP1], a ; (3)
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ldh [rP1], a ; (3)
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xor a ; (1)
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ldh [rP1], a
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ret
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