* New: In Anabatic::DiodeWire, use "antennaDiodeMaxWL" to compute the number
of diodes to insert in a wire only cluster. Use boxes instead of segments
to define the area as segments can be splitted by the diodes inserteds
at the DiodeRps stage.
* New: In DiodeWire::createDiodes(), specific diode insertion method.
Try to instert first in long horizontal wires.
When a long *horizontal* wire connect to a cluster, an antenna effect
may be created *before* the METAL3 is deposited, if the cluster's diode
is not *directly* connected to the gate through *only* METAL2. So, we
add a "forced halo" where the long horizontal connecting wires will be
broken by a diode *near* the gate. This problem do not occur for long
connecting METAL3, as the diode will be connected by then. Note that
we are hard-coding the gauge routing direction in the algorithm.
With that modification, only one antenna effect remains in LibreSOC
LS180. May be corrected by post-treatement.
* New: In Anabatic::DiodeCluster::mergeForcedhalo() add specific secondary
areas where diode must be insterted in addition to the one of the
RroutingPad cluster. To "isolate" the cluster from long horizontal
wires.
Protecting clusters of sinks is not enough. There can be very long
wires that far exceed the protection capacity of one diode. Instead
of putting a bunch of diodes near the sinks, we choose to put them
regularly along the interconncting wires.
With this approach we are down to 7 antenna violations on LibreSOC
LS180 test chip.
This will get less good results on arlet6502 & ao6800 because of the
core being a long way from the I/O pads. Should create jumpers on thoses,
but it is for later.
First part of the antenna effect protection : diode insertions.
Anabatic::antennaProtect(Net*) and it's supporting infrastructure
has been rewritten & simplificated. Must be used in conjuction
with the "Flexlib" bloat model of Etesian. A cursory description
of the algorithm has been added in the source file.
* New: GCell::hasNet() to tell if net is going through a GCell,
either as a straigth wire or has a local GContact (turn,
branch, terminal).
* New: Etesian::BloatFlexib class (tagged "Flexlib") suited for
flexlib uses. It is derived from "nsxlib".
To have enough space to insert all the wanted diodes, we
enlarge "mx2_x2" & "mx3_x2" of resp. 1 and 2 pitches.
This is an empiric finding, Yosys seems very fond of thoses
gates and we often see them underneath area where no space
was available to put a diode... May need some more fine grained
analysis.
* Change: In EtesianEngine::globalPlace(), disable the call to
antennaProtect(). First reason is that, after all, Coloquinte
do not handle so well the resizing of the cells "on the fly",
it overspill the boundaries sometimes. Second reason is that
as we cannot know the routing tree at this stage, we will not
be able to choose the correct points for diode insertions.
We only have a Steiner tree wich may not be the same as a
density driven Dijkstra.
* Change: In Etesian::Area, the Occurrence to the Instances where
not stored in a uniform way. Some where starting from the
placed sub-block, some where starting from the top level
(corona), making their processing (and remembering it) tricky.
Now, they are all expressed from the top cell (corona).
The coordinate system is now systematically the one of the
top block (*not* the block).
Create various overloaded functions EtesianEngine::toCell()
and EtesianEngine::toBlock() to ease Occurrence & coordinate
translations.
* New: In Etesian::Slice::createDiodeUnder(), add a X position hint.
Search is done by going through the whole slice range and
minimizing the distance to the hint. If it starts to be too
slow, we may optimize.
* Bug: In EtesianEngine::toColoquinte(), the placement of the top
level external pins was not taken into account (this at last
explain their weird positioning).
* New: AnabaticEngine::antennaProtect(), new algorithm to avoid
antenna effect. This step must be done *after* global routing
and *before* detailed routing. This way we have access to the
real routing and can mend it (along with the netlist) to
insert diodes at the rigth points.
From the global routing we build clusters (DiodeCluster) of
RoutingPads connected through a set of wire whose total length
is below the antenna effect threshold. Long wires connecting the
clusters are also tagged because we need to put a diode between
them and the first RoutingPad of the cluster. This is to avoid
a long METAL2 wire connecting to the RoutingPad before the diode is
connected through METAL3 (in case of misalignment).
This protection is not even enough. For *very long* wires, we
needs to put *more* than one diode (this is to be implemented).
Jean-Paul Chaput