use first free IOCB for "GRAPHICS 0" call instead of using a hard-coded one

libsrc/atari/crt0.s

@@ -20,6 +20,7 @@
 	.import		sram_init
 .if .defined(__ATARIXL__)
 	.import		scrdev
+	.import		findfreeiocb
 .endif
 
         .include        "zeropage.inc"
@@ -181,11 +182,9 @@ _exit:  jsr     donelib         ; Run module destructors
 	sta	APPMHI+1
 
 
-
 ; ... issue a GRAPHICS 0 call (copied'n'pasted from TGI drivers)
 
-
+	jsr	findfreeiocb
-	ldx	#$50		; take any IOCB, hopefully free (@@@ fixme)
 
         ; Reopen it in Graphics 0
         lda     #OPEN
@@ -203,8 +202,10 @@ _exit:  jsr     donelib         ; Run module destructors
         lda     #0
         sta     ICBLH,x
         jsr     CIOV_org
-
+; add error checking here...
-
+        lda     #CLOSE
+        sta     ICCOM,x
+        jsr     CIOV_org
 
 .endif
 

libsrc/atari/shadow_ram_prepare.s

@@ -122,7 +122,17 @@ sramprep:
 ; ... issue a GRAPHICS 0 call (copied'n'pasted from TGI drivers)
 
 
-        ldx     #$50            ; take any IOCB, hopefully free (@@@ fixme)
+        jsr     findfreeiocb
+.ifdef DEBUG		; only check in debug version, this shouldn't happen normally(tm)
+        beq     iocbok
+        print_string "Internal error, no free IOCB!"
+        jsr     delay
+        jsr     delay
+        jsr     delay
+        jsr     restore                 ; restore stuff we've changed
+        jmp     (DOSVEC)                ; abort loading
+iocbok:
+.endif
 
         ; Reopen it in Graphics 0
         lda     #OPEN
@@ -140,20 +150,18 @@ sramprep:
         lda     #>screen_device_length
         sta     ICBLH,x
         jsr     CIOV_org
-        bpl     okoko
+        bpl     scrok
 
+; shouldn't happen(tm)
         print_string "Internal error, aborting..."
         jsr     delay
         jsr     delay
         jsr     delay
-
+        jsr     restore                 ; restore stuff we've changed
         jmp     (DOSVEC)                ; abort loading
 
 
-okoko:
+scrok:  ; now close it again -- we don't need it anymore
-
-
-        ; Now close it again; we don't need it anymore :)
         lda     #CLOSE
         sta     ICCOM,x
         jsr     CIOV_org
@@ -266,6 +274,7 @@ no_copy:
 .endif
         rts
 
+.include "findfreeiocb.inc"
 
 ; my 6502 fu is rusty, so I took a routine from the internet (http://www.obelisk.demon.co.uk/6502/algorithms.html)
 
@@ -298,6 +307,21 @@ done:   rts
 .endproc
 
 
+; clean up after a fatal error
+
+restore:lda     RAMTOP_save
+        sta     RAMTOP
+        lda     MEMTOP_save
+        sta     MEMTOP
+        lda     MEMTOP_save+1
+        sta     MEMTOP+1
+        lda     APPMHI_save
+        sta     APPMHI
+        lda     APPMHI_save+1
+        sta     APPMHI+1
+        rts
+
+
 .byte "HERE ****************** HERE ***************>>>>>>"
 
 sramsize: