Subj : Re: Closing a file in Assembly on the VIC-20
To   : Lawrence Woodman
From : Tilmann Hentze
Date : Thu Jun 17 2021 11:29 am

Lawrence Woodman <lorrywoodman@gmail.com> wrote:
> I have created a piece of code which replicates the problem below if
> anyone has any ideas where I'm going wrong I'd be very grateful.

> ; Basic Stub
> TOK_SYS     = $9E             ; SYS token

>             .byt  $01, $10    ; Load address ($1001)

>             * = $1001
>             .word basicEnd    ; Next Line link, here end of Basic program
>             .word 1           ; The line number for the SYS statement
>             .byt  TOK_SYS     ; SYS token
>             .asc  " "
>             .asc  "4110"      ; Start of machine language
>             .byt  0           ; End of Basic line
> basicEnd    .word 0           ; End of Basic program

> ; KERNEL/BASIC ROM Routines
> CLOSE       = $FFC3
> SAVE        = $FFD8
> SETLFS      = $FFBA
> SETNAM      = $FFBD


> main
>             lda  #$07         ; Length of file name
>             ldx  #<filename   ; Low byte of file name location
>             ldy  #>filename   ; High byte of file name location
>             jsr  SETNAM       ; Set the name

>             lda  #$08         ; Logical file number
>             ldx  #$08         ; Device number
>             ldy  #$01         ; Secondary address - $01 because saving
>             jsr  SETLFS       ; Set above parameters

I'd switch the two previous blocks around, so that you first set up the
channel and then set the file name.

>             lda  #<flash      ; Low byte of start of memory block to save
>             sta  $C1
>             lda  #>flash      ; High byte of start of memory block to save
>             sta  $C2

>             lda  #$C1            ; Pointer to location of start address
>             ldx  #<(flashend+1)  ; Low byte of (end of memory block + 1)
>             ldy  #>(flashend+1)  ; High byte of (end of memory block + 1)

The high byte should probaly only increment, when the low byte is $ff.

>             jsr  SAVE            ; Perform save

>             lda  #$08         ; Logical file number
>             jsr  CLOSE        ; Close the file

Looks good to me. Perhaps it will work with the first mentioned change?

Best regards,
Tilmann.
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