Added a specialized callirq routine

git-svn-id: svn://svn.cc65.org/cc65/trunk@2968 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/runtime/Makefile

@@ -41,6 +41,7 @@ OBJS = 	add.o		\
        	bneg.o		\
        	bpushbsp.o	\
        	call.o		\
+        callirq.o       \
         callmain.o      \
        	compl.o		\
 	condes.o	\

libsrc/runtime/callirq.s

@@ -0,0 +1,53 @@
+;
+; Ullrich von Bassewitz, 2004-04-04
+;
+; CC65 runtime: Support for calling special irq routines declared as condes
+; type 2.
+;
+; There are two reasons, why this is a separate routine, and the generic
+; condes routine in condes.s is not used:
+;
+;   1. Speed. Having several things hardcoded makes it faster. This is
+;      important if it is called in each interrupt.
+;
+;   2. Reentrancy. The condes routines must use self modyfiying code, which
+;      means it is not reentrant. An IRQ using condes, that interrupts
+;      another use of condes will cause unpredicatble behaviour. The current
+;      code avoids this by using locking mechanisms, but it's complex and
+;      has a size and performance penalty.
+;
+; As the normal condes routine, this one has the limitation of 127 table 
+; entries.
+;
+
+       	.export	callirq
+
+       	.import	__IRQFUNC_TABLE__, __IRQFUNC_COUNT__
+
+.code
+
+; --------------------------------------------------------------------------
+; Call all IRQ routines. The function needs to use self modifying code and
+; is thereforce placed in the data segment.
+; NOTE: The routine must not be called if the table is empty!
+
+.data
+
+.proc	callirq
+
+        ldy     #.lobyte(__IRQFUNC_COUNT__)
+loop:   dey
+        lda     __IRQFUNC_TABLE__+1,y
+        sta     jmpvec+2                ; Modify code below
+     	dey
+        lda     __IRQFUNC_TABLE__+0,y
+        sta     jmpvec+1                ; Modify code below
+       	sty    	index+1                 ; Modify code below
+jmpvec: jsr    	$FFFF                   ; Patched at runtime
+index: 	ldy    	#$FF                    ; Patched at runtime
+       	bne     loop
+        rts
+
+.endproc
+
+

libsrc/runtime/condes.s

@@ -52,9 +52,8 @@ exit:   rts
 
 
 ; --------------------------------------------------------------------------
-; Generic table call handler. Since the routine is also used to call a table
-; of interrupt handlers, it uses heavily self modifying code for performance
-; reasons. It will go into the data segment for this reason ...
+; Generic table call handler. The code uses self modifying code and goes
+; into the data segment for this reason.
 ; NOTE: The routine must not be called if the table is empty!
 
 .data