cx16diskio.f_read() now correctly deals with banked ram boundary

compiler/res/prog8lib/cx16/cx16diskio.p8

@@ -102,6 +102,8 @@ cx16diskio {
                 goto byte_read_loop     ; macptr block read not supported, do fallback loop
             diskio.list_blocks += size
             bufferpointer += size
+            if msb(bufferpointer) == $c0
+                bufferpointer = mkword($a0, lsb(bufferpointer))  ; wrap over bank boundary
             num_bytes -= size
             if c64.READST() & $40 {
                 diskio.f_close()       ; end of file, close it

compiler/res/prog8lib/diskio.p8

@@ -226,6 +226,8 @@ close_end:
     sub f_read(uword bufferpointer, uword num_bytes) -> uword {
         ; -- read from the currently open file, up to the given number of bytes.
         ;    returns the actual number of bytes read.  (checks for End-of-file and error conditions)
+        ;    NOTE: on systems with banked ram (such as Commander X16) this routine DOES NOT
+        ;          automatically load into subsequent banks if it reaches a bank boundary!
         if not iteration_in_progress or not num_bytes
             return 0
 

docs/source/todo.rst

@@ -3,7 +3,6 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
-- bug: f_read() can't deal with running out of banked ram? maybe only cx16diskio.f_read()?
 - add McCarthy evaluation to shortcircuit and/or expressions.  Both conditional expressions and assignments!
 - add some more optimizations in vmPeepholeOptimizer
 - vm Instruction needs to know what the read-registers/memory are, and what the write-register/memory is.

examples/cx16/zsound/stream-test-zcm.p8

@@ -36,13 +36,9 @@ zsound_lib:
 
     ubyte load_ok = false
 
-    sub prebuffer() {
+    sub prebuffer()  {
         txt.print("prebuffering...")
-        repeat 4 {
-            void cx16diskio.f_read(digi_address, ram_bank_size)
-            txt.print_ub(cx16.getrambank())
-            txt.spc()
-        }
+        void cx16diskio.f_read(digi_address, ram_bank_size*4)
     }
 
     sub start() {