Re: [myhdl-list] A newbie question about the sequential conversion example

[Christopher F. <chr...@gm...>]

On 3/20/2015 6:08 AM, Jeremy Herbert wrote:
> Hi all,
>
> I'm trying to get my head around myhdl, as I am definitely a python fan and
> I'd like to try and use it for verilog generation. But there is a little
> too much magic going on in one of the examples for me, and I was wondering
> if someone could help me out.
>
> I'm looking at the first example on
> http://docs.myhdl.org/en/latest/manual/conversion_examples.html#conv-usage
> under "A small sequential design". The first problem I have is that in the
> docstring of the Inc function it references a variable "n". But n is not
> present as function argument or anywhere in the code. Huh?

Yes, that is an error, we will get it fixed ASAP.

I believe what happened, is that the example originally
did have an "n" and then it was modified.

>
> Next, just below it, there is the following line:
>
> inc_inst = toVerilog(Inc, count, enable, clock, reset, n=n)
>
> The keyword argument 'n' is now set as equal to the variable n, which isn't
> defined and also isn't used in the Inc function. What's going on here?
> Where is this n coming from?

As you suspected, this is an error sorry for any
confusion.  The example should be stated as (remove
the `n`):


     from myhdl import *

     def Inc(count, enable, clock, reset):
         """ Incrementer with enable.
         count -- output
         enable -- control input, increment when 1
         clock -- clock input
         reset -- asynchronous reset input
         """

         @always_seq(clock.posedge, reset=reset)
         def incLogic():
             if enable:
                 count.next = count + 1

         return incLogic


     m = 8

     count = Signal(modbv(0)[m:])
     enable = Signal(bool(0))
     clock  = Signal(bool(0))
     reset = ResetSignal(0, active=0, async=True)

     inc_inst = Inc(count, enable, clock, reset)


     inc_inst = toVerilog(Inc, count, enable, clock, reset)
     ** ToVerilogWarning: Output port is read internally: count


Regards,
Chris