rework for the initial CBDOS

src/dos_m65/dos_unitnum.s

@@ -0,0 +1,53 @@
+
+;
+; Unit number handling. For detailed description see 'm65dos_bridge.s' file
+;
+
+
+dos_UNITNUM:
+
+	; Check if memory content is not damaged
+
+	jsr dos_MEMCHK
+	bcs dos_UNITNUM_none
+
+	; Check what kind of device was requested
+
+	cmp #$00
+	beq dos_UNITNUM_sdcard
+	cmp #$01
+	beq dos_UNITNUM_floppy
+	cmp #$02
+	beq dos_UNITNUM_ramdisk
+
+	lda #$00
+
+	; FALLTROUGH
+
+dos_UNITNUM_none:
+
+	sec
+	rts
+
+dos_UNITNUM_sdcard:
+
+	lda UNIT_SDCARD
+
+	+skip_2_bytes_trash_nvz
+
+dos_UNITNUM_floppy:
+
+	lda UNIT_FLOPPY
+
+	+skip_2_bytes_trash_nvz
+
+dos_UNITNUM_ramdisk:
+
+	lda UNIT_RAMDISK
+
+	cmp #$00
+	beq dos_UNITNUM_none
+
+	clc
+	rts
+