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40 lines
1.0 KiB
ArmAsm
40 lines
1.0 KiB
ArmAsm
;
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; 2020-05-02, Greg King
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;
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; unsigned char __fastcall__ vera_layer_enable (unsigned char layers);
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; /* Display the layers that are "named" by the bit flags in layers.
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; ** A value of 0b01 shows layer 0, a value of 0b10 shows layer 1,
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; ** a value of 0b11 shows both layers. Return the previous value.
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; */
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;
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.export _vera_layer_enable
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.include "cx16.inc"
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mask = VERA::DISP::ENABLE::LAYER1 | VERA::DISP::ENABLE::LAYER0
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.proc _vera_layer_enable
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stz VERA::CTRL ; Use display register bank 0
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asl a
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asl a ; Shift new flags into position
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asl a
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asl a
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ldy VERA::DISP::VIDEO
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eor VERA::DISP::VIDEO
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and #mask
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eor VERA::DISP::VIDEO ; Replace old flags with new flags
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sta VERA::DISP::VIDEO
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tya
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and #mask ; Get old flags
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lsr a
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lsr a
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lsr a
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lsr a
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ldx #>$0000
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rts
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.endproc
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