33 lines
922 B
ArmAsm
33 lines
922 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 302
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;; - [CM64] Compute's Mapping the Commodore 64 - page 224
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;; - https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
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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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tksa:
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;; Due to TKSA/SECOND command encoding (see https://www.pagetable.com/?p=1031),
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;; allowed channels are 0-15; report error if out of range
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cmp #$10
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bcs kernalerror_FILE_NOT_INPUT
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ora #$F0
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sta BSOUR
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jsr iec_tx_command
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bcs + ; branch if error
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;; XXX - is it really the right place to do a turnaround? I've got some doubts
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;; (it forces us to send the TKSA command 'manually' sometimes), but
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;; Luigi Di Fraia (https://luigidifraia.wordpress.com/2017/06/27/codebase64-on-the-kernal-behaviour/)
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;; claims TKSA Kernal routine actually does the turnaround
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jmp iec_turnaround_to_listen
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*
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rts
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