23 lines
498 B
ArmAsm
23 lines
498 B
ArmAsm
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;;
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;; Checks whether device numbe (in .A) is a correct IEC device number
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;;
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;; Preserves .A, .X and .Y
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;;
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iec_devnum_check:
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;; 0, 1, 2, or 3 are illegal - reserved for non-IEC devices on Commodore
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cmp #$04
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bcs +
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;; FALLTROUGH
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iec_devnum_check_failed:
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sec ; indicate non-IEC device
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rts
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*
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;; 31 and above are illegal too, due to IEC command encoding scheme,
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;; see https://www.pagetable.com/?p=1031
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cmp #$1F
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bcs iec_devnum_check_failed
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;; Carry is clear here - indicates IEC device
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rts
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