Answers Database
CoolRunner/XPLA Professional: What can be done to get a better fit if a design does not fit into the selected device?
Record #7504
Product Family: Software
Product Line: CoolRunner
Product Part: XPLA Fitter
Problem Title:
CoolRunner/XPLA Professional: What can be done to get a better fit if a design does not fit
into the selected device?
Problem Description:
Urgency: Hot
General Description: My design does not fit into the selected device. What can I do?
Solution 1:
There are many things you can do to make a design fit into a selected
device. If at all possible, you might consider a larger device particularly
if the below suggestions do not work.
You must first determine why the design demands more resources than
the selected device allows. The error message you receive may help.
For example, if it says "Design exceeds maximum number of nodes",
you can use the number that follows to determine how many macrocells
the design requires for the current XPLA Professional settings. If the
error message says "Unable to fit design", more investigation is required.
Targeting the next larger device can help determine the resources
required. If the design fits into the next larger device, look at the fitter
report (*.fit file). The top portion of the file shows used resources. Keeping
in mind the resources available for the smaller device, you can often get
an idea for where the limiting item is.
If clocks, asynchronous reset/preset, or output enables are the limiting
item, you may be able to fit the design by reducing the amount of these
particular resources. For example, if clocks are the limiting item, try to
drive the equations with fewer clocks or perhaps use an Enhanced
Clock device. These devices have more clocks available than the
original devices. If removing any of these items is not possible for your
design, you will need to use the next larger device.
If product terms are the limiting item, it may be possible to fit the design
by adjusting the "Max P-Terms Per Equation" setting in the Properties
window of XPLA Professional. A smaller number on this setting will
create more nodes thereby reducing the amount of product terms
utilized in the logic block. This is seen with fewer product terms used
in the PLA. This, however reduces the maximum speed at which the
part can operate.
If macrocells are an issue, raising the number on the "Max P-Terms
Per Equation" setting will reduce the macrocell used. Doing this can
cause product terms to become a limiting item since more of the PLA
may be used which is limited in size.
If fan-in to the product terms is the limiting item, there is an unpublished
option that can be implemented. By simultaneously pressing
[CTRL][ALT]Z you can get to the "More Options" window. This window
allows you to specify the maximum permissible fan-in per equation for
synthesis and fitting. The synthesis setting specifies the maximum number
of signal fan-in allowed per equation. The fitter setting specifies the
maximum number of signal fan-in per logic block. Generally speaking,
reducing the synthesis setting will force more nodes to be created during
synthesis. The subsequent fitting procedure, with a larger setting value,
may allow equations with similar signals to share fan-in possibly allowing
the design to fit.
The default setting for the fan-in is 36 for both synthesis and fitter. It is
possible to increase the value to 40. This can often help when fan-in is
the limiting item. Please note: Raising this value above the default value
will greatly reduce the ability of your design to fit again with changes while
retaining a fixed pinout.
End of Record #7504 - Last Modified: 02/07/00 18:38 |
