Re: [myhdl-list] Reset functionality "synthesis"

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

On 07/03/2012 06:40 PM, Angel Ezquerra wrote:

>
> Jan,
>
> given how contentious the asynchronous vs synchronous reset debate is
> I would argue that there should be no default value in this case, and
> that the reset type should always be set explicitly.

I am quite surprized by this, is this really so contentious?
In my whole career as a design engineer, I don't recall one
single incident about this (many about other issues :-)).

Actually, I have *always* used the mixed approach, where you
go into reset asynchronously, but come out of it synchronously.
In this method, the reset driver comes out of a ff that
is reset asychronously with the primary reset, and that
also synchronizes the primary reset.

For this to work, the ffs in the design should have
an asynchronous reset, but that doesn't mean the
reset scheme itself is asynchronous, as described.
The big advantage of this method is that you don't
need the clock to be present to go into reset,
only to come out of it. So you avoid power-up issues
with clocks and pll's.

I thought this was the standard practice, which is why
I intuitively made it the default.

I'd like to hear more opinions.

-- 
Jan Decaluwe - Resources bvba - http://www.jandecaluwe.com
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