cc65/libsrc/apple2/dioopen.s

;
; Oliver Schmidt, 24.03.2005
;
; dhandle_t __fastcall__ dio_open (unsigned char device);
;

        .export 	_dio_open
        .import 	return0, __dos_type, isdevice

        .include	"errno.inc"
        .include	"mli.inc"

_dio_open:
        ; Check for ProDOS 8
        ldx	__dos_type
        bne	:+
        lda	#$01		; "Bad system call number"
        bne	oserr		; Branch always

        ; Check for valid device
:       tax
        jsr	isdevice
        beq	:+
        lda	#$28		; "No device connected"

        ; Return oserror
oserr:  sta	__oserror
        jmp	return0

        ; Return success
:       txa
        asl
        asl
        asl
        asl
        ldx	#$00
        stx	__oserror
        rts