docs/library/micropython: Document the newer micropython functions.

docs/library/micropython.rst

@@ -7,6 +7,32 @@
 Functions
 ---------
 
+.. function:: const(expr)
+
+   Used to declare that the expression is a constant so that the compile can
+   optimise it.  The use of this function should be as follows::
+
+    from micropython import const
+
+    CONST_X = const(123)
+    CONST_Y = const(2 * CONST_X + 1)
+
+   Constants declared this way are still accessible as global variables from
+   outside the module they are declared in.  On the other hand, if a constant
+   begins with an underscore then it is hidden, it is not available as a global
+   variable, and does not take up any memory during execution.
+
+   This `const` function is recognised directly by the MicroPython parser and is
+   provided as part of the `micropython` module mainly so that scripts can be
+   written which run under both CPython and MicroPython, by following the above
+   pattern.
+
+.. function:: opt_level([level])
+
+   If `level` is given then this function sets the optimisation level for subsequent
+   compilation of scripts, and returns `None`.  Otherwise it returns the current
+   optimisation level.
+
 .. function:: alloc_emergency_exception_buf(size)
 
    Allocate ``size`` bytes of RAM for the emergency exception buffer (a good
@@ -35,3 +61,56 @@ Functions
    The information that is printed is implementation dependent, but currently
    includes the number of interned strings and the amount of RAM they use.  In
    verbose mode it prints out the names of all RAM-interned strings.
+
+.. function:: stack_use()
+
+   Return an integer representing the current amount of stack that is being
+   used.  The absolute value of this is not particularly useful, rather it
+   should be used to compute differences in stack usage at different points.
+
+.. function:: heap_lock()
+.. function:: heap_unlock()
+
+   Lock or unlock the heap.  When locked no memory allocation can occur and a
+   `MemoryError` will be raised if any heap allocation is attempted.
+
+   These functions can be nested, ie `heap_lock()` can be called multiple times
+   in a row and the lock-depth will increase, and then `heap_unlock()` must be
+   called the same number of times to make the heap available again.
+
+.. function:: kbd_intr(chr)
+
+   Set the character that will raise a `KeyboardInterrupt` exception.  By
+   default this is set to 3 during script execution, corresponding to Ctrl-C.
+   Passing -1 to this function will disable capture of Ctrl-C, and passing 3
+   will restore it.
+
+   This function can be used to prevent the capturing of Ctrl-C on the
+   incoming stream of characters that is usually used for the REPL, in case
+   that stream is used for other purposes.
+
+.. function:: schedule(fun, arg)
+
+   Schedule the function `fun` to be executed "very soon".  The function
+   is passed the value `arg` as its single argument.  "very soon" means that
+   the MicroPython runtime will do its best to execute the function at the
+   earliest possible time, given that it is also trying to be efficient, and
+   that the following conditions hold:
+
+   - A scheduled function will never preempt another scheduled function.
+   - Scheduled functions are always executed "between opcodes" which means
+     that all fundamental Python operations (such as appending to a list)
+     are guaranteed to be atomic.
+   - A given port may define "critical regions" within which scheduled
+     functions will never be executed.  Functions may be scheduled within
+     a critical region but they will not be executed until that region
+     is exited.  An example of a critical region is a preempting interrupt
+     handler (an IRQ).
+
+   A use for this function is to schedule a callback from a preempting IRQ.
+   Such an IRQ puts restrictions on the code that runs in the IRQ (for example
+   the heap may be locked) and scheduling a function to call later will lift
+   those restrictions.
+
+   There is a finite stack to hold the scheduled functions and `schedule`
+   will raise a `RuntimeError` if the stack is full.