Re: [myhdl-list] Driving constants

[Jan D. <ja...@ja...>]

On 09/03/2011 12:39 PM, Sébastien Bourdeauducq wrote:
> Hi,
>
> I need to create instances that only drive their output to some constant
> level, e.g. the equivalent of:
>
> module foo(output bar);
> assign bar = 1'b1;
> endmodule
>
> I have tried doing:
> 	def ImplementControl(self):
> 		@always_comb
> 		def logic():
> 			self.control.ack_o.next[0] = 1
> 		return logic
>
> but MyHDL doesn't cope with the empty sensitivity list.
>
> Setting the value at signal creation (e.g. things like
> self.control.ack_o = Signal(intbv(1))) is not an option because it would
> become very messy with my object-oriented approach. Besides, I would
> find it surprising that describing something as basic as a constant
> driver is an intractable problem in MyHDL.
>
> Any solutions?

A signal that you don't drive in your code gives you a warning
and the expected assign. To me, that is exactly what
"constant" means. I don't see what's messy about it.

Of course, one could use such a signal in an always_comb
and assign it to another signal. Such an approach would be
meaningful for parametrization (a signal which is sometimes
a constant, in other cases driven in code).

Jan

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