32 lines
689 B
ArmAsm
32 lines
689 B
ArmAsm
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;;
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;; Official Kernal routine, described in:
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;;
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;; - [RG64] C64 Programmer's Reference Guide - page 303
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;; - [CM64] Compute's Mapping the Commodore 64 - page 224
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;;
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;; CPU registers that has to be preserved (see [RG64]): .X, .Y
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;;
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;; XXX currently does not preserve registers, to be fixed!
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unlsn:
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;; This routine is documented in 'Compute's Mapping the Commodore 64', page 224
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;; First check whether we have something to be sent in the buffer
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lda C3PO
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beq +
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lda BSOUR
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sec ; send it with EOI
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jsr iec_tx_byte ; XXX what about the status of this operation?
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;; Mark the buffer as invalid
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lda #$00
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sta C3PO
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*
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;; Buffer empty send the command
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lda #$3F
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jmp iec_tx_command
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