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--- extensions_tutorial [2019/12/12 11:10] – [Adding new functions] neils
+++ extensions_tutorial [2019/12/12 11:36] – [Referencing XC=BASIC symbols in assembly language] neils
@@ Line 51: / Line 51: @@
 Simply use the [[fun|FUN ... ENDFUN]] block to define new functions.
-==== Referencing XC=BASIC symbols in assembly language ====
+===== Referencing XC=BASIC symbols in assembly language =====
 To speed things up, you should write functions in assembly language. To be able to do this, you need to know how to access **XC=BASIC** symbols and features in assembly. The following table serves as a guide:
@@ Line 70: / Line 70: @@
   fun joy_firepressed!(port!)
-    rem -- we start
+    dim result!
     asm "
+      ; This is how to refer to a function's argument
+      lda {self}.port
+      ; Port #2 becomes 0, Port #1 remains 1
+      ora #%00000001
+      tax
+      ; This is how to refer to a global constant
+      lda _JOY_PORT2, x
+      ora #%00001000
+      eor #%00001000
+      lsr
+      lsr
+      lsr
+      ; A now holds the return value of our function
+      ; Write it to the variable "result!"
+      sta {self}.result
     "
+    return result!
   endfun