In the LS180, probably due to the implementation of a small RAM
with DFFs, some leaf of the clock tree (H-Tree) got heavily
loaded (around 80 DFFs sinks). Implement an option that allow
the leaf of the QuadTree to use three buffers instead of one.
The sinks are partitionned using their angle from the center
of the leaf (trigonometric direction). CChoose the bigger angle
gaps to perform the split.
* Change: In Cumulus/plugins.block.configuration.GaugeConf, in
getNearestHorizontalTrack() and getNearestVerticalTrack() add an
offset argument to shift the position of the requested track
by a certain amount.
* Change: In Cumulus/plugins.block.configuration.GaugeConf, in
createHorizontal(), add a flag to make the source end of the
segment to "stick out". Useful when connecting to a stacked
VIA top, but using a lower layer that can be shifted.
* New: In Cumulus/plugins.block.spares.Spares, BufferPool & QuadTree,
add support for selection and management of multiple buffers at
the same time. Basically returns a list of selected buffer
instances instead of just one instance.
Added HEAVY_LEAF_LOAD flag to Spares. To be used by all tools
classes that makes use of it.
Added QuadTree.runselect(), be sure to call it between different
H-Tree operations, otherwise results will be strange.
* New: In Cumulus/plugins.block.htree.HTree, in case of heavy leaf
load, in the leaf of the tree, allocate three buffers instead
of one. Select them to form a triangle around the main one.
That is, use (i,j), (i+1,j) and (i,j+1).
Added a HTree._connectLeaf() to share the handling of the child
buffer connexions. Whether they are leaf of not and heavy or not.
* Change: Cumulus/plugins.block.Block, expand HTree support to
manage the HEAVY_LEAF_LOAD flag.
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