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Add ability to constrain flop harness to specific side of PBlock #1318

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04776e0
Add ability to constraint InlineFlops to a specific side of the PBloc…
abutt-amd Nov 7, 2025
35c8c33
Use regex for port side map
abutt-amd Nov 11, 2025
7b0734e
Merge remote-tracking branch 'origin/array_builder' into performance-…
abutt-amd Nov 11, 2025
df12be1
Address comments
abutt-amd Nov 12, 2025
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201 changes: 188 additions & 13 deletions src/com/xilinx/rapidwright/design/tools/InlineFlopTools.java
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,8 @@
import com.xilinx.rapidwright.util.Pair;
import com.xilinx.rapidwright.util.StringTools;

import static com.xilinx.rapidwright.util.Utils.isCLB;

/**
* Set of tools to add/remove flip flops inline to top level port connections.
* This is targeted at kernel replication preparation prior to routing to ensure
Expand Down Expand Up @@ -94,6 +96,103 @@ public static void createAndPlaceFlopsInlineOnTopPortsNearPins(Design design, St
createAndPlaceFlopsInlineOnTopPorts(design, clkNet, keepOut, true);
}

private static Site shiftSiteToSide(Device device, Site site, PBlock pblock, PBlockSide side) {
Tile topLeftTile = pblock.getTopLeftTile();
Tile bottomRightTile = pblock.getBottomRightTile();
Tile siteTile = site.getTile();
int pBlockTop = topLeftTile.getRow();
int pBlockLeft = topLeftTile.getColumn();
int pBlockRight = bottomRightTile.getColumn();
int pBlockBottom = bottomRightTile.getRow();
int siteTileCol = siteTile.getColumn();
int siteTileRow = siteTile.getRow();

Tile shiftedTile;
if (side == PBlockSide.TOP) {
// Shift tile up
shiftedTile = shiftTileUntilSlice(device, pBlockTop, siteTileCol, true, true);
} else if (side == PBlockSide.LEFT) {
// Shift tile left
shiftedTile = shiftTileUntilSlice(device, siteTileRow, pBlockLeft, false, true);
} else if (side == PBlockSide.RIGHT) {
// Shift tile right
shiftedTile = shiftTileUntilSlice(device, siteTileRow, pBlockRight, false, false);
} else {
// Shift tile down
shiftedTile = shiftTileUntilSlice(device, pBlockBottom, siteTileCol, true, false);
}
Site shiftedSite = site.getCorrespondingSite(site.getSiteTypeEnum(), shiftedTile);
if (shiftedSite == null) {
// Can't find a site on the edge of the PBlock, return the original site
return site;
}

return shiftedSite;
}

/**
* Add flip-flops inline on all the top-level ports of an out-of-context design.
* This is useful for out-of-context kernels so that after the flops have been
* placed, the router is forced to route connections of each of the ports to
* each of the flops. This can help alleviate congestion when the kernels are
* placed/relocated in context.
*
* @param design The design to modify
* @param clkNet Name of the clock net to use on which to add the flops
* @param keepOut The pblock used to contain the kernel and the added flops will
* not be placed inside this area.
* @param portSideMap Map from ports to side of the pblock the flop should be placed on
*/
public static void createAndPlacePortFlopsOnSide(Design design, String clkNet, PBlock keepOut,
Map<EDIFPort, PBlockSide> portSideMap) {
assert (design.getSiteInsts().isEmpty());
Site start = keepOut.getAllSites("SLICE").iterator().next(); // TODO this is a bit wasteful
boolean exclude = true;

EDIFHierNet clk = design.getNetlist().getHierNetFromName(clkNet);

Set<SiteInst> siteInstsToRoute = new HashSet<>();

for (Map.Entry<EDIFPort, PBlockSide> entry : portSideMap.entrySet()) {
EDIFPort port = entry.getKey();
PBlockSide side = entry.getValue();
if (port.getName().equals(clkNet)) {
continue;
}
Site shiftedSite = shiftSiteToSide(design.getDevice(), start, keepOut, side);
if (port.isBus()) {
for (int i : port.getBitBlastedIndicies()) {
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@clavin-xlnx clavin-xlnx Nov 11, 2025

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This is a lot of duplicated code. I realize this is partly due to the nature of bussed vs. single bit ports. One way to work around this is to use this pattern:

            for (int i : (port.isBus() ? port.getBitBlastedIndicies() : new int[] { 0 })) {
                EDIFPortInst portInst = port.getInternalPortInstNameFromIndex(i));

A better solution might be to modify EDIFPort.getBitBlastedIndicies() so that for the single bit case it returns a static new int[] { 0 }.

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@abutt-amd abutt-amd Nov 12, 2025

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We decided that getBitBlastedIndicies should be updated to return { 0 } when called on a non-bused port. I will refactor further once this change has been made.

EDIFPortInst inst = port.getInternalPortInstFromIndex(i);
if (allLeavesAreIBUF(design, inst)) {
continue;
}

Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(shiftedSite, keepOut, exclude).iterator();
siteItr.next(); // Skip the first site, as we are suggesting one inside the pblock
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr, null);
Cell flop = createAndPlaceFlopInlineOnTopPortInst(design, inst, loc, clk);
siteInstsToRoute.add(flop.getSiteInst());
}
} else {
EDIFPortInst inst = port.getInternalPortInst();
if (inst != null) {
if (allLeavesAreIBUF(design, inst)) {
continue;
}

Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(shiftedSite, keepOut, exclude).iterator();
siteItr.next(); // Skip the first site, as we are suggesting one inside the pblock
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr, null);
Cell flop = createAndPlaceFlopInlineOnTopPortInst(design, inst, loc, clk);
siteInstsToRoute.add(flop.getSiteInst());
}
}
}
for (SiteInst si : siteInstsToRoute) {
si.routeSite();
}
}

/**
* Add flip-flops inline on all the top-level ports of an out-of-context design.
* This is useful for out-of-context kernels so that after the flops have been
Expand All @@ -114,8 +213,6 @@ private static void createAndPlaceFlopsInlineOnTopPorts(Design design, String cl
EDIFCell top = design.getTopEDIFCell();
Site start = keepOut.getAllSites("SLICE").iterator().next(); // TODO this is a bit wasteful
boolean exclude = true;
Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(start, keepOut, exclude).iterator();
siteItr.next(); // Skip the first site, as we are suggesting one inside the pblock

EDIFHierNet clk = design.getNetlist().getHierNetFromName(clkNet);

Expand All @@ -135,7 +232,9 @@ private static void createAndPlaceFlopsInlineOnTopPorts(Design design, String cl
if (centroidPlacement) {
netCentroidFlipFlopPlacement(design, inst, keepOut, clk, siteInstsToRoute);
} else {
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr);
Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(start, keepOut, exclude).iterator();
siteItr.next(); // Skip the first site, as we are suggesting one inside the pblock
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr, null);
Cell flop = createAndPlaceFlopInlineOnTopPortInst(design, inst, loc, clk);
siteInstsToRoute.add(flop.getSiteInst());
}
Expand All @@ -150,7 +249,9 @@ private static void createAndPlaceFlopsInlineOnTopPorts(Design design, String cl
if (centroidPlacement) {
netCentroidFlipFlopPlacement(design, inst, keepOut, clk, siteInstsToRoute);
} else {
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr);
Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(start, keepOut, exclude).iterator();
siteItr.next(); // Skip the first site, as we are suggesting one inside the pblock
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr, null);
Cell flop = createAndPlaceFlopInlineOnTopPortInst(design, inst, loc, clk);
siteInstsToRoute.add(flop.getSiteInst());
}
Expand All @@ -174,6 +275,64 @@ private static boolean allLeavesAreIBUF(Design design, EDIFPortInst inst) {
return allLeavesAreIBUF;
}

private static Tile shiftTileUntilSlice(Device device, int row, int col, boolean shiftRow, boolean negativeShift) {
int offset = negativeShift ? -1 : 1;
Tile shiftedTile = null;
while (shiftedTile == null || !isCLB(shiftedTile.getTileTypeEnum())) {
int shiftedRow = shiftRow ? row + offset : row;
int shiftedCol = !shiftRow ? col + offset : col;
if (shiftRow && (shiftedRow < 0 || shiftedRow > device.getRows())) {
shiftedTile = null;
break;
}
if (!shiftRow && (shiftedCol < 0 || shiftedCol > device.getColumns())) {
shiftedTile = null;
break;
}
shiftedTile = device.getTile(shiftedRow, shiftedCol);
offset = negativeShift ? offset - 1 : offset + 1;
}
return shiftedTile;
}

private static Site getSiteOnPBlockEdgeClosestToSite(Device device, Site site, PBlock pblock) {
Tile topLeftTile = pblock.getTopLeftTile();
Tile bottomRightTile = pblock.getBottomRightTile();
Tile siteTile = site.getTile();
int pBlockTop = topLeftTile.getRow();
int pBlockLeft = topLeftTile.getColumn();
int pBlockRight = bottomRightTile.getColumn();
int pBlockBottom = bottomRightTile.getRow();
int siteTileCol = siteTile.getColumn();
int siteTileRow = siteTile.getRow();
int topDist = siteTileRow - pBlockTop;
int bottomDist = pBlockBottom - siteTileRow;
int leftDist = siteTileCol - pBlockLeft;
int rightDist = pBlockRight - siteTileCol;

Tile shiftedTile = null;
if (topDist <= leftDist && topDist <= rightDist && topDist <= bottomDist) {
// Shift tile up
shiftedTile = shiftTileUntilSlice(device, pBlockTop, siteTileCol, true, true);
} else if (leftDist <= topDist && leftDist <= rightDist && leftDist <= bottomDist) {
// Shift tile left
shiftedTile = shiftTileUntilSlice(device, siteTileRow, pBlockLeft, false, true);
} else if (rightDist <= topDist && rightDist <= leftDist && rightDist <= bottomDist) {
// Shift tile right
shiftedTile = shiftTileUntilSlice(device, siteTileRow, pBlockRight, false, false);
} else {
// Shift tile down
shiftedTile = shiftTileUntilSlice(device, pBlockBottom, siteTileCol, true, false);
}
Site shiftedSite = site.getCorrespondingSite(site.getSiteTypeEnum(), shiftedTile);
if (shiftedSite == null) {
// Can't find a site on the edge of the PBlock, return the original site
return site;
}

return shiftedSite;
}

private static void netCentroidFlipFlopPlacement(Design design, EDIFPortInst inst, PBlock keepOut, EDIFHierNet clk,
Set<SiteInst> siteInstsToRoute) {
EDIFHierCellInst topInst = design.getNetlist().getTopHierCellInst();
Expand All @@ -192,17 +351,23 @@ private static void netCentroidFlipFlopPlacement(Design design, EDIFPortInst ins
if (!points.isEmpty()) {
Site centroid = ECOPlacementHelper.getCentroidOfPoints(design.getDevice(), points,
VALID_CENTROID_SITE_TYPES);
Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(centroid, keepOut, true).iterator();
siteItr.next();
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr);
Site shiftedCentroid = getSiteOnPBlockEdgeClosestToSite(design.getDevice(), centroid, keepOut);
Iterator<Site> siteItr = ECOPlacementHelper.spiralOutFrom(shiftedCentroid, keepOut, true).iterator();
if (keepOut.containsTile(shiftedCentroid.getTile())) {
siteItr.next();
}
Pair<Site, BEL> loc = nextAvailPlacement(design, siteItr, shiftedCentroid.getTile().getSLR());
Cell flop = createAndPlaceFlopInlineOnTopPortInst(design, inst, loc, clk);
siteInstsToRoute.add(flop.getSiteInst());
}
}

private static Pair<Site, BEL> nextAvailPlacement(Design design, Iterator<Site> itr) {
private static Pair<Site, BEL> nextAvailPlacement(Design design, Iterator<Site> itr, SLR slr) {
while (itr.hasNext()) {
Site curr = itr.next();
if (slr != null && curr.getTile().getSLR() != slr) {
continue;
}
SiteInst candidate = design.getSiteInstFromSite(curr);
List<BEL> usedFFs = new ArrayList<>();
if (candidate != null) {
Expand Down Expand Up @@ -272,14 +437,17 @@ public static void removeInlineFlops(Design design) {
Net vcc = design.getVccNet();
Set<SitePinInst> vccPins = new HashSet<>();
pinsToRemove.put(vcc, vccPins);
String[] staticPins = new String[]{"CKEN1", design.getSeries() == Series.Versal ? "RST" : "SRST1"};
String[] staticPins = new String[]{"CKEN1", "CKEN2", design.getSeries() == Series.Versal ? "RST" : "SRST1"};
for (EDIFCellInst inst : design.getTopEDIFCell().getCellInsts()) {
if (inst.getName().endsWith(INLINE_SUFFIX)) {
Cell flop = design.getCell(inst.getName());
SiteInst si = flop.getSiteInst();
// Assume we only placed one flop per SiteInst
siteInstToRemove.add(si);
for (SitePinInst pin : si.getSitePinInsts()) {
if (pin.getNet().isGNDNet()) {
continue;
}
pinsToRemove.computeIfAbsent(pin.getNet(), p -> new HashSet<>()).add(pin);
}
for (String staticPin : staticPins) {
Expand All @@ -292,9 +460,7 @@ public static void removeInlineFlops(Design design) {
}
}

for (SiteInst si : siteInstToRemove) {
design.removeSiteInst(si);
}

DesignTools.batchRemoveSitePins(pinsToRemove, true);

String[] ctrlPins = new String[]{"C", "R", "CE"};
Expand All @@ -303,7 +469,9 @@ public static void removeInlineFlops(Design design) {
// Remove control set pins
for (String pin : ctrlPins) {
EDIFPortInst p = c.getPortInst(pin);
p.getNet().removePortInst(p);
if (p != null && p.getNet() != null) {
p.getNet().removePortInst(p);
}
}
// Merge 'D' sources and 'Q' sinks, restore original net
EDIFPortInst d = c.getPortInst("D");
Expand Down Expand Up @@ -336,6 +504,13 @@ public static void removeInlineFlops(Design design) {
design.removeCell(c.getName());
}

for (SiteInst si : siteInstToRemove) {
boolean isStaticSource = si.getSitePinInsts().stream()
.anyMatch((p) -> p.getNet().isGNDNet() && p.isOutPin());
if (!isStaticSource) {
design.removeSiteInst(si);
}
}
}

public static void main(String[] args) {
Expand Down
31 changes: 31 additions & 0 deletions src/com/xilinx/rapidwright/design/tools/PBlockSide.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
/*
*
* Copyright (c) 2025, Advanced Micro Devices, Inc.
* All rights reserved.
*
* Author: Andrew Butt, AMD Advanced Research and Development.
*
* This file is part of RapidWright.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/

package com.xilinx.rapidwright.design.tools;

public enum PBlockSide {
LEFT,
RIGHT,
TOP,
BOTTOM
}
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