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.

Apple2/RPi.Command.asm

@@ -17,10 +17,15 @@ XLEN       =  $BE52    ;length of command string-1.
 XCNUM      =  $BE53    ;CI cmd no. (ext cmd - 0).
 PBITS      =  $BE54    ;Command parameter bits.
 XRETURN    =  $FF58    ;Known RTS instruction.
-InputByte = $c08e
-OutputByte = $c08d
-InputFlags = $c08b
-OutputFlags = $c087
+
+; have 6502 absolute indexed access phantom reads 
+; happen on page $bf to avoid unwanted i/o access
+IndexOffset = $8f
+
+InputByte = $c08e - IndexOffset
+OutputByte = $c08d - IndexOffset
+InputFlags = $c08b - IndexOffset
+OutputFlags = $c087 - IndexOffset
 
 ReadBlockCommand = $01
 WriteBlockCommand = $02
@@ -76,9 +81,10 @@ DetectSlot:
  asl
  asl
  asl
- tax
  clc
- bcc Start
+ adc #IndexOffset
+ tax
+ bcc Start ;always
 nextSlot:
  dex
  bne DetectSlot

Apple2/Shell.asm

@@ -19,10 +19,14 @@ IOError = $27
 NoDevice = $28
 WriteProtect = $2B
 
-InputByte = $c08e
-OutputByte = $c08d
-InputFlags = $c08b
-OutputFlags = $c087
+; have 6502 absolute indexed access phantom reads 
+; happen on page $bf to avoid unwanted i/o access
+IndexOffset = $8f
+
+InputByte = $c08e - IndexOffset
+OutputByte = $c08d - IndexOffset
+InputFlags = $c08b - IndexOffset
+OutputFlags = $c087 - IndexOffset
 
 ResetCommand = $00
 ReadBlockCommand = $01
@@ -85,9 +89,10 @@ DetectSlot:
  asl
  asl
  asl
- tax
  clc
- bcc Init
+ adc #IndexOffset
+ tax
+ bcc Init ;always
 nextSlot:
  dex
  bne DetectSlot