Re: [myhdl-list] delays misconverted in VHDL conversion

[Henry G. <he...@ca...>]

On 08/02/15 22:22, Josy Boelen wrote:
> Henry Gomersall <heng <at> cantab.net> writes:
>
>> >
>> >I'm trying to do a poor man's RTL co-simulation by creating the files
>> >needed for simulation and the relevant stimulus files (from the MyHDL
>> >simulation), then writing the outputs from the Xilinx simulation to
> file
>> >for post-simulation comparison. For this I need a clock.
>> >
>> >Consider:
>> >
>> >def ClkDriver(clk, period=20):
>> >
>> >      lowTime = int(period/2)
>> >      highTime = period - lowTime
>> >
>> >       <at> instance
>> >      def driveClk():
>> >          while True:
>> >              yield delay(lowTime)
>> >              clk.next = 1
>> >              yield delay(highTime)
>> >              clk.next = 0
>> >
>> >      return driveClk
>> >
>> >This is converted to the following (pertinent) VHDL:
>> >
>> >architecture MyHDL of ClkDriver is
>> >
>> >constant lowTime: integer := 10;
>> >constant highTime: integer := 10;
>> >
>> >begin
>> >
>> >CLKDRIVER_DRIVECLK: process is
>> >begin
>> >      while True loop
>> >          wait for lowTime ns;
>> >          clk <= '1';
>> >          wait for highTime ns;
>> >          clk <= '0';
>> >      end loop;
>> >      wait;
>> >end process CLKDRIVER_DRIVECLK;
>> >
>> >end architecture MyHDL;
>> >
>> >Xilinx Vivado complains this is a syntax error. It doesn't like the
> use
>> >of a constant in the "wait for lowTime ns", though it's easily fixed
>> >with e.g. "wait for 10 ns".
>> >
>> >Is this Vivado being crap, or is this expected behaviour? I could
> always
>> >create my own custom VHDL template, but it would be neater to have
> MyHDL
>> >do it for me.
>> >
>> ><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.

Can anyone else comment on whether this wants to be fixed? Happy to 
raise a PR with some form of a fix. I feel this could easily go into 0.9.

My reading of the spec suggests the ns is an integral part of the time 
type, not some general numerical attribute, so I think the failure is 
expected.

Cheers,

Henry