33 lines
904 B
ArmAsm
33 lines
904 B
ArmAsm
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//
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// Helper routine to check for EOI while receiving byte from IEC
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//
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iec_rx_check_eoi:
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// Wait for talker to pull CLK.
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// If over 200 usec (205 cycles on NTSC machine) , then it is EOI.
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// Loop iteraction takes 13 cycles, 17 full iterations are enough
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ldx #$11 // 2 cycles
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!:
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lda CIA2_PRA // 4 cycles
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rol // 2 cycles, to put CLK in as the last bit
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bpl iec_rx_check_eoi_done // 2 cycles if not jumped
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dex // 2 cycles
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bne !- // 3 cycles if jumped
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// Timeout - either this is the last byte of stream, or the stream is empty at all.
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// Mark end of stream in IOSTATUS
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jsr kernalstatus_EOI
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// Pull data for 60 usec to confirm it
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jsr iec_release_clk_pull_data
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jsr iec_wait60us
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jsr iec_release_clk_data
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iec_rx_check_eoi_done:
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rts
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