Turned the 'ST' status byte into a symbol resolved by the linker in order to allow to use it from code living in the 'cbm' directory.

Moved getdevice.s from 'c64'/'c128' to 'cbm' making use of the new 'ST' setup.

git-svn-id: svn://svn.cc65.org/cc65/trunk@5834 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/cbm/Makefile

@@ -76,6 +76,7 @@ S_OBJS =	c_acptr.o	\
                 filename.o      \
                 filetype.o      \
                 filevars.o      \
+                getdevice.o     \
 		gotox.o 	\
 		gotoxy.o 	\
 		gotoy.o 	\

libsrc/cbm/getdevice.s

@@ -0,0 +1,66 @@
+;
+; Oliver Schmidt, 2012-09-04
+;
+; unsigned char getfirstdevice (void);
+; unsigned char __fastcall__ getnextdevice (unsigned char device);
+;
+
+        .export         _getfirstdevice
+        .export         _getnextdevice
+
+        .import         isdisk
+        .import         opencmdchannel
+        .import         closecmdchannel
+        .importzp       ST
+        .importzp       tmp2
+
+;------------------------------------------------------------------------------
+; _getfirstdevice
+
+_getfirstdevice:
+        lda     #$FF
+        ; Fall through
+
+;------------------------------------------------------------------------------
+; _getnextdevice
+
+_getnextdevice:
+        tax
+next:	inx
+        cpx     #$FF
+        beq     done
+
+; [open|close]cmdchannel already call isdisk internally but they
+; interpret a non-disk as a no-op while we need to interpret it
+; as an error here
+
+        jsr     isdisk
+        bcs     next
+
+; [open|close]cmdchannel don't call into the Kernal at all if they
+; only [in|de]crement the reference count of the shared cmdchannel
+; so we need to explicitly initialize ST here
+
+        lda     #$00
+        sta     ST
+
+        stx     tmp2
+        jsr     opencmdchannel
+        ldx     tmp2
+        jsr     closecmdchannel
+        ldx     tmp2
+
+; As we had to reference ST above anyway we can as well do so
+; here too (instead of calling READST)
+
+        lda     ST
+
+; Either the Kernal calls above were successfull or there was
+; already a cmdchannel to the device open - which is a pretty
+; good indication of its existence ;-)
+
+        bmi     next
+
+done:   txa
+        ldx     #$00
+        rts