myhdl/doc/source/whatsnew/0.9.rst

.. currentmodule:: myhdl

.. _new09:

***********************
What's new in MyHDL 0.9
***********************

Python 3 support
================

Experimental Python 3 support has been added to MyHDL 0.9.
This was a major effort to modernize the code. As a result,
Python 2 and 3 are supported from a single codebase.

See :doc:`/python3` for more info.

Interfaces (Conversion of attribute accesses)
=============================================

Rationale
---------

Complex designs often have many signals that are passed to different levels of
hierarchy.  Typically, many signals logically belong together. This can be
modelled by an *interface*: an object that has a number of :class:`Signal`
objects as its attributes.  Grouping signals into an interface simplifies the
code, improves efficiency, and reduces errors.

The following is an example of an *interface* definition::

    class Complex:
        def __init__(self, min=-2, max=2):
	    self.real = Signal(intbv(0, min=min, max=max))
	    self.imag = Signal(intbv(0, min=min, max=max))


Although previous versions supported interfaces for modeling, they were not 
convertible.  MyHDL 0.9 now supports conversion of designs that use interfaces.

The following is an example using the above ``Complex`` interface definition::

    a,b = Complex(-8,8), Complex(-8,8)
    c = Complex(-128,128)

    def complex_multiply(clock, reset, a, b, c):

        @always_seq(clock.posedge, reset=reset)
        def cmult():
            c.real.next = (a.real*b.real) - (a.imag*b.imag)
	    c.imag.next = (a.real*b.imag) + (a.imag*b.real)

	return cmult
	           

Solution
--------

The proposed solution is to create unique names for attributes which are used
by `MyHDL generator`_\s.  The converter will create a unique name by using the
name of the parent and the name of the attribute along with the name of the
MyHDL module instance. The converter will essentially replace the "." with an
"_" for each interface element. In essence, interfaces are supported
using hierarchical name expansion and name mangling. 

Note that the MyHDL convertor supports interfaces, even though
the target HDLs do not. This is another great example where the
convertor supports a high-level feature that is not available
in the target HDLs.

See also
--------
For additional information see the original proposal `mep-107`_.

.. _mep-107: http://dev.myhdl.org/meps/mep-107.html
.. _MyHDL generator: http://docs.myhdl.org/en/latest/manual/reference.html#myhdl-generators-and-trigger-objects

Other noteworthy improvements
=============================

``ConcatSignal`` interface
--------------------------

The interface of :class:`ConcatSignal` was enhanced. In
addition to signals, you can now also use constant values 
in the concatenation.

``std_logic`` type ports 
------------------------

:func:`toVHDL` has a new attibute ``std_logic_ports``. When
set, only ``std_logic`` type ports are used in the interface
of the top-level VHDL module.

Development flow
----------------

The MyHDL development flow has been modernized by moving to git and `github`_
for version control. In addition, travis has set up so that all pull requests
are tested automatically, enabling continuous intergration.

Acknowledgments
===============

The Python 3 support effort was coordinated by Keerthan Jaic, who also
implemented most of if. Convertible interfaces were championed by Chris Felton,
and implemented by Keerthan Jaic.

MyHDL development is a collaborative effort, as can be seen on `github`_.
Thanks to all who contributed with suggestions, issues and pull requests.

.. _github: https://www.github.com/jandecaluwe/myhdl