Re: [cc65] Why does this work in 128 mode but not 64 mode?

I solved the problem by creating me a function to call that checks the drive
status and returns it.  I was very careful to follow all the steps set forth
in the C128 PRG and the result works in both C128 and C64 modes equally.  I
am sure there's improvements to be made here as the shell of the method was
stubbed out in C and I then modified the resulting assembler code spit out
by CC65.

.setcpu "6502"
.smart on
.autoimport on
.case on
.importzp sp, sreg, regsave, regbank, tmp1, ptr1, ptr2
.macpack longbranch

.export _checkDrive

.proc _checkDrive
JSR pusha ; Store the accumulator

JSR decsp4

; Let's get the drive number, we use it last
 LDY #$04 ; SP(4) is the third parameter
 LDA (sp),y ; Get the value from the stack
 LDY #$01 ; SP(1) is the drive variable
 STA (sp),y ; Store the value in the variable

; Let's get the length, we use it first
LDY #$07 ; SP(7) is the first parameter
 LDA (sp),y ; Retrieve the parameter
 LDY #$00 ; SP(0) is the length variable
 STA (sp),y ; Store A to the variable
 PHA ; Push A (length)

; Let's get the command, we use it next to last
 LDY #$06 ; SP(6,5) is the second parameter
 JSR ldaxysp ; Loads A and X from SP
 LDY #$02 ; SP(2,3) is the string variable
 JSR staxysp ; Save the string pointer to SP(2)
 ; Prepare for the SETNAM call
PHA ; A -> Stack (high)
 TXA ; X -> A (low)
TAY ; A -> Y (low)
 PLA ; Stack -> A (high)
TAX ; A -> X (high)
 PLA ; Stack -> A (length)
; At this point, A should have the length,
 ; X should have the high byte of the string pointer
; and Y should have the low byte of the string pointer
 JSR $FFBD ; SETNAM

 ; Prepare for the SETLFS
LDY #$01 ; Variable for drive number
 LDA (sp),y ; Load A with drive number
 TAX ; A -> X (drive number)
LDY #15 ; 15 -> Y (secondary address)
 ; At this point, A and X should both have
; the drive number and Y should have secondary
 ; address of 15.
JSR $FFBA ; SETLFS (drive, drive, 15)

; Call open and handle the results;
JSR $FFC0 ; OPEN
 PHA ; Push result to stack

; Close our open channel
 LDY #$01 ; Get the drive number again
 LDA (sp),y ; from sp(1)
 JSR $FFC3 ; CLOSE

 ; Get the error status back into A
error: PLA ; Retrieve result from stack

; We're done, go home.
JSR incsp8 ; Increment the SP
 RTS ; We're done.
.endproc

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