AR# 1270

XACT-CPLD: Using a guide (.GYD) file to define pin constraints for CPLDs

Description

Keywords: pin-locking, cpld, cst, gyd

Urgency: Standard

General Description:
In the XACT-CPLD flow, a Constraint File (.CST) is only used to
control timing constraints. Placement constraints are not
recognized in a CST file.

Xilinx recommends that all placement constraints be put
in the source design file (either Schematic or Equation-based).
However, it is possible to place PIN assignments in a guide
file (.GYD), and have the software treat these as constraints.

The GYD file is really intended for guiding placement off a
previous implementation. However, with the current software,
pin assignments in the .GYD file and in the design file are
treated the same, and so it is possible to edit a
previously-generated .GYD file to add pin constraints as
desired.

Solution

1

XACT 6.0.1

How to lock pins using a .GYD file for CPLDs:

1. Fit the design (Implement from Design Manager).
This will automatically produce a file entitled <design>.gyd
and place it in your project directory under the correct
version.
(example: C:\MYDESIGN\XPROJECT\V1_6\DESIGN.GYD)

2. Edit this file to lock down pins. It looks something like:

CLK PIN20
INPUT1 PIN45
...
...
with CLK and INPUT1 referring to I/O signals in the design.

In this case, CLK will be assigned to pin 20, and INPUT1 will
be assigned to pin 45.

If you are targetting one of the Grid-Array packages, then the
syntax will be like:

CLK PINF3
INPUT1 PINA12
.
.
Where the signal CLK will be assigned to pin F3, and INPUT1
will be assigned to pin A12.

3. In the Design Manager in Windows, select Tools->FlowEngine.
In the Flow Engine select Setup->Advanced...
In the Flow Configuration box use the Browse option to select
the path to the .GYD file you just edited. Continue with
design implementation as usual.

2

The guide (.GYD) file is case sensitive in M1.3/M1.4 release.

AR# 1270
Date 10/07/2008
Status Archive
Type General Article