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Avoid unwanted i/o access.
Depending on the 6502, LDA addr,X and/or STA addr,X produce additional phantom reads. In order to avoid those phantom reads to do i/o access, I used the "classic" approach of moving those reads from page $C0 to page $BF.
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@ -17,10 +17,15 @@ XLEN = $BE52 ;length of command string-1.
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XCNUM = $BE53 ;CI cmd no. (ext cmd - 0).
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PBITS = $BE54 ;Command parameter bits.
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XRETURN = $FF58 ;Known RTS instruction.
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InputByte = $c08e
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OutputByte = $c08d
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InputFlags = $c08b
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OutputFlags = $c087
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; have 6502 absolute indexed access phantom reads
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; happen on page $bf to avoid unwanted i/o access
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IndexOffset = $8f
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InputByte = $c08e - IndexOffset
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OutputByte = $c08d - IndexOffset
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InputFlags = $c08b - IndexOffset
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OutputFlags = $c087 - IndexOffset
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ReadBlockCommand = $01
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WriteBlockCommand = $02
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@ -76,9 +81,10 @@ DetectSlot:
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asl
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asl
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asl
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tax
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clc
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bcc Start
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adc #IndexOffset
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tax
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bcc Start ;always
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nextSlot:
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dex
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bne DetectSlot
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@ -19,10 +19,14 @@ IOError = $27
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NoDevice = $28
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WriteProtect = $2B
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InputByte = $c08e
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OutputByte = $c08d
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InputFlags = $c08b
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OutputFlags = $c087
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; have 6502 absolute indexed access phantom reads
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; happen on page $bf to avoid unwanted i/o access
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IndexOffset = $8f
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InputByte = $c08e - IndexOffset
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OutputByte = $c08d - IndexOffset
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InputFlags = $c08b - IndexOffset
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OutputFlags = $c087 - IndexOffset
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ResetCommand = $00
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ReadBlockCommand = $01
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@ -85,9 +89,10 @@ DetectSlot:
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asl
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asl
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asl
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tax
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clc
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bcc Init
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adc #IndexOffset
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tax
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bcc Init ;always
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nextSlot:
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dex
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bne DetectSlot
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