Re: [myhdl-list] delays in VHDL conversion

[Josy B. <jos...@gm...>]

Henry Gomersall <heng <at> cantab.net> writes:

> 
> On 08/02/15 22:22, Josy Boelen wrote:
> <snip>
> > Actually the converted code is wrong, the statements like:
> >      constant lowTime: integer := 10;
> >      wait for lowTime ns;
> >
> > are incorrect, they should either be:
> >      constant lowTime: integer := 10;
> >      wait for lowTime * 1.0 ns;
> >
> > or:
> >      constant lowTime: time := 10.0 ns;
> >      wait for lowTime ;
> >
> > Should be easy to fix in the MyHDL code.
> 
> You mean in the conversion routines? The easiest way I can think of is 
> to replace the "ns" string with "* 1.0 ns"
> here:
> 
https://bitbucket.org/jandecaluwe/myhdl/src/b07b52398020b3bd737d0b4f1574
f0d94eefccb5/myhdl/conversion/_toVHDL.py?at=default#cl-970
> 
> No doubt that will break other things though? Is there a reason why 
> there can't always be a multiplier (other than code neatness)?
> <snip>

I meant exactly that, and the '* 1.0 ns' would be my preferred too, and 
is definitely the easiest. I don't think this will break any other code.

Specifically setting the 'times' using real numbers, e.g.:
  def ClkDriver(clk, period=20.0):

     lowTime = period / 2
     highTime = period - lowTime
     ...
     wait for lowTime ns;

will not help either, as VHDL expects a time-type value and the 'ns' is 
part of that and can not be used as a units specifier. I'm not aware if 
there is a cast to convert something (int or real) into a time-type. Of 
course we could write the function(s) to do this and add these to the 
MyHDL package and modify the MyHDL code:
 elif f is delay:
            self.write( "to_VHDLtime( ")
            self.visit(node.args[0])  # this will end up in visit_Num() 
and produce an integer or a real (I suppose)
            self.write(" )")
            return

Regards,

Josy