01-25-2011 04:32 PM
I would appreciate some help here, because this is not clear to me why this is happening.
Okay, in plan ahead, we have two (well in fact three) Netlist views.
1. RTL netlist
2. Synth netlist
3. Implementation netlist
Okay in the synthesis netlist, if you look at all the instances (in the netlist view), they all are displayed as an “i” inside a yellow rectangle, with NO blue stripe (which makes sense, because we haven't placed any constraint on them yet).
But, after the implementation, when you look at the Netlist view. we will see most of the instances are displayed as an “i” inside a yellow rectangle with a blue stripe, which is indicative of the fact that there are some constraints assigned to it.
HOWEVER, even after place & route, I still see some instances without a blue stripe, which is telling me that those instances have no constraint assigned to them (http://www.xilinx.com/support/documentation/sw_manuals/xilinx12_2/PlanAhead_UserGuide.pdf page 136).
But first of all:
isn't it that at the minimum all the instances should meet the period constraint?
In other words, if there is not additional constraints set, at least each instance since will be located in a path between two synchronous elements, that means they have to be constraint with the period (at the minimum).
So, even when after the implementation, I still see instances (e.b. LUT5, LUT6, FDC, ...) that are not constrained.
Also, the instances that are not constrained, even after place&route, they CANNOT be viewed in the 'Device view' ?!???
Although, they are there in the schematic view.
Is this a limitation of the 'Device view' ? Or is this an issue with the software?
Because, I selected a random path, where it happens that I have few LUT5s that are not constraints. But they are there in the 'Schematic View', so there have to be there on the die too. But 'Device view' doesn't show them??
But I still don't understand how it is that some of the instances can still have no constraints assigned, even after place&route.
In my case, in the schematic view that I randomly selected, I see two LUTs in between two FDCs, but isn't it that the tool still has to put them in a way for them to meet timing (period) ??
So, there still has to be some sort of period constraints assigned to those LUTs.
But even if it is not, then where are there? I am not able to see them in the 'Device view', because they don't have 'blue stripe' symbol notation.
I would appreciate some help.
01-25-2011 10:57 PM