diff --git a/compiler/res/prog8lib/cx16/graphics.p8 b/compiler/res/prog8lib/cx16/graphics.p8
index b9269b468..e3d303ad2 100644
--- a/compiler/res/prog8lib/cx16/graphics.p8
+++ b/compiler/res/prog8lib/cx16/graphics.p8
@@ -2,9 +2,10 @@
 %import syslib
 %import textio
 
-; bitmap pixel graphics module for the CommanderX16
+; Bitmap pixel graphics module for the CommanderX16
 ; wraps the graphics functions that are in ROM.
-; only black/white monchrome 320x200 for now.
+; only black/white monchrome 320x200 for now. (i.e. truncated at the bottom)
+; For full-screen 640x480 or 320x240 graphics, use the "gfx2" module instead. (but that is Cx16-specific)
 
 graphics {
     const uword WIDTH = 320
@@ -133,5 +134,3 @@ graphics {
         cx16.FB_set_pixel(1)
     }
 }
-
-
diff --git a/compiler/src/prog8/ast/processing/AstChecker.kt b/compiler/src/prog8/ast/processing/AstChecker.kt
index e83d81820..9b3bd4424 100644
--- a/compiler/src/prog8/ast/processing/AstChecker.kt
+++ b/compiler/src/prog8/ast/processing/AstChecker.kt
@@ -202,6 +202,9 @@ internal class AstChecker(private val program: Program,
         if(subroutine.name in BuiltinFunctions)
             err("cannot redefine a built-in function")
 
+        if(subroutine.parameters.size>16)
+            err("subroutines are limited to 16 parameters")
+
         val uniqueNames = subroutine.parameters.asSequence().map { it.name }.toSet()
         if(uniqueNames.size!=subroutine.parameters.size)
             err("parameter names must be unique")
diff --git a/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt
index 6ab14877f..8212ff867 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt
@@ -47,21 +47,19 @@ internal class FunctionCallAsmGen(private val program: Program, private val asmg
                     // just a single parameter, no risk of clobbering registers
                     argumentViaRegister(sub, IndexedValue(0, sub.parameters.single()), stmt.args[0])
                 } else {
-                    // multiple register arguments, risk of register clobbering.
-                    // evaluate arguments onto the stack, and load the registers from the evaluated values on the stack.
                     when {
                         stmt.args.all {it is AddressOf ||
                                 it is NumericLiteralValue ||
                                 it is StringLiteralValue ||
                                 it is ArrayLiteralValue ||
                                 it is IdentifierReference} -> {
-                            // no risk of clobbering for these simple argument types. Optimize the register loading.
+                            // There's no risk of clobbering for these simple argument types. Optimize the register loading directly from these values.
                             for(arg in sub.parameters.withIndex().zip(stmt.args)) {
                                 argumentViaRegister(sub, arg.first, arg.second)
                             }
                         }
                         else -> {
-                            // Risk of clobbering due to complex expression args. Work via the stack.
+                            // Risk of clobbering due to complex expression args. Work via the evaluation stack.
                             registerArgsViaStackEvaluation(stmt, sub)
                         }
                     }
diff --git a/examples/cx16/gfx2.p8 b/examples/cx16/gfx2.p8
index 952ed68d7..00e81d185 100644
--- a/examples/cx16/gfx2.p8
+++ b/examples/cx16/gfx2.p8
@@ -1,10 +1,17 @@
+%target cx16
 %import textio
 %import graphics
 %import test_stack
 %zeropage basicsafe
 %option no_sysinit
 
-; TODO full-screen graphics mode library, in development.  (as replacement for the graphics routines in ROM that are constrained to 200 vertical pixels and lores mode only)
+; Bitmap pixel graphics module for the CommanderX16
+; Custom routines to use the full-screen 640x480 and 320x240 screen modes.
+; This is only compatible with the Cx16.
+; For compatible graphics code that words on C64 too, use the "graphics" module instead.
+
+
+; TODO this is in development.
 
 
 main {
diff --git a/examples/test.p8 b/examples/test.p8
index 8aa7d92e7..7d042e0ab 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -23,12 +23,16 @@ main {
 
     sub start () {
         txt.chrout('!')
-        ubyte bank = 1
+        uword bank = 1
         uword address = 1000
         ubyte value = 123
         bank++
-        vpoke(bank, address, value)
-        vpokeasm(address, bank, value)      ; TODO generates params on stack if expression is used such as lsb(bank).  CHECK STACK UNWINDING!!!
+
+        test_stack.test()
+        vpoke(lsb(bank), address, value)
+        test_stack.test()
+        vpokeasm(address, lsb(bank), value)      ; TODO generates params on stack if expression is used such as lsb(bank).  CHECK STACK UNWINDING!!!
+        test_stack.test()
         ; TODO also see if we can do this via R0-R15 temp registers rather than using the estack???
     }
 }