Since signals that traverse the global ZIA incur either a 2nS (XCR320) or 4nS (XCR960) delay, it is sometimes necessary to group timing-critical signals within a fast module.
This is accomplished using the property, FM_GROUP. This property can be specified in a ABEL source file or in a control file.
Example: (Please note the spacing.)
fm_group siga sigb sigc
This instructs the fitter to place the list of signals specified with this property in the same fast module. Note that the use of this property alone does not specify a particular fast module for the placement of the signals; it only indicates that these signals should be grouped together. To specify a particular fast module for the group of signals, simply assign one of the signals in the group a node or pin number from that fast module.