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 Python 3 Support for more info.

Interfaces (Conversion of attribute accesses)


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 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


The proposed solution is to create unique names for attributes which are used by MyHDL generators. 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 converter supports interfaces, even though the target HDLs do not. This is another great example where the converter supports a high-level feature that is not available in the target HDLs.

See also

For additional information see the original proposal mep-107.

Other noteworthy improvements

ConcatSignal interface

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

std_logic type ports

toVHDL has a new attribute 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.


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.