[Discuss-gnuradio] Re: failed timing when generating rbf for usrp_std

[Matt Ettus]

Martin Dvh wrote:
> Hi Matt,
> 
> I get a failed timing when I try to build the rbf for usrp_std.
> 
> Any idea why this is?
> 
> (This is a cvs checkout of a few days ago)
> 
> 
> I use QuartusII 5.1 including service pack 1
> 
> (I only tried the usrp_std_config_4rx_0tx version)
> 
> // Uncomment this for 4 rx channels (w/o halfband) & 0 transmit channels
> `include "usrp_std_config_4rx_0tx.vh"
> 
> The reports are in:
> http://www.olifantasia.com/pub/projects/gnuradio/mdvh/usrp-failed-timing/fpga/toplevel/usrp_std/


>From the report you can see that the timing problems are all on paths
involving setting registers.  Since these are set once before all the
signal processing is enabled, they do not affect anything.  You can
safely ignore them.

When I used to work on CPUs and ASICs we called these "multicycle paths"
and had some sort of filter so they would not be flagged as problems in
the timing checks.  If anybody knows how to do that in the Quartus flow
I'd love to hear.  Even better, submit a patch...

Matt