Achronix ACE Version 5.0 - Manual (Page 247)

Advanced Concepts Chapter 3. Concepts
Advanced Concepts
The following are advanced concepts intended primarily for extremely experienced users, or users being
actively guided by Achronix FAEs.
Clock Regions
Synchronous fabrics (like those found in the 22iHD family) deal with numerous clocks. Due to physical
routing limitations, only a finite number of clocks can be routed to each individual site within the fabric. To
keep the placement/routing problem space manageable for the most complex designs, a fabric is divided
up into Clock Regions of a relatively coarse granularity, where each Clock Region as a whole allows a finite
number of clocks to be routed within that clock region.
Each fabric is divided up into a number of Clock Regions of roughly similar area. The exact numbers of
clock regions, the dimensions of each region, the number and types of sites within the region, the allowed
sources of the clocks routed to each region, and the differences (like skew) of clock behavior between clock
regions will all be specified by the chosen target device. A subset of this information is presented in the
Clock Regions view . See the technical specification of the target device for complete details.
For designs with an extremely large number of clocks, the use of Placement Region Constraints may be
necessary to guide placement decisions regarding Clock Regions. This should be discussed thoroughly
with an Achronix FAE first, as improper use of Placement Region Constraints can lower QOR or even cause
Placement or Routing to become unsolvable.
235 http://www.achronix.com UG001 Rev. 5.0 - 5th December 2012