Added functions to learn about the unit numbers of the ProDOS 8 devices found.

git-svn-id: svn://svn.cc65.org/cc65/trunk@4663 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/apple2/drives.s

@@ -0,0 +1,38 @@
+;
+; Oliver Schmidt, 2010-05-24
+;
+; unsigned char drivecount (void);
+; unsigned char* drivelist (void);
+;
+
+        .export         _drivecount, _drivelist
+        .import         __dos_type
+
+        .include        "mli.inc"
+
+_drivecount:
+        ldx     #$00
+
+        ; Check for ProDOS 8
+        lda     __dos_type
+        bne     :+
+        rts
+
+        ; Number of on-line devices (minus 1)
+:       ldy     DEVCNT
+        iny
+        tya
+        rts
+
+_drivelist:
+        ldx     #$00
+
+        ; Check for ProDOS 8
+        lda     __dos_type
+        bne     :+
+        rts
+
+        ; Up to 14 units may be active
+:       lda     #<DEVLST
+        ldx     #>DEVLST
+        rts