timing_opt: Functions to calculate arc delay limits

Signed-off-by: David Shah <dave@ds0.me>

common/timing.cc

@@ -85,14 +85,7 @@ struct CriticalPath
     delay_t path_period;
 };
 
-// Data for the timing optimisation algorithm
-struct NetCriticalityInfo
-{
-    // One each per user
-    std::vector<delay_t> slack;
-    std::vector<float> criticality;
-    unsigned max_path_length = 0;
-};
+
 
 typedef std::unordered_map<ClockPair, CriticalPath> CriticalPathMap;
 typedef std::unordered_map<IdString, NetCriticalityInfo> NetCriticalityMap;
@@ -599,6 +592,7 @@ struct Timing
                         nc.criticality.at(i) = std::max(nc.criticality.at(i), criticality);
                     }
                     nc.max_path_length = std::max(nc.max_path_length, nd.max_path_length);
+                    nc.cd_worst_slack = std::min(nc.cd_worst_slack, worst_slack.at(startdomain.first));
                 }
             }
         }
@@ -914,4 +908,11 @@ void timing_analysis(Context *ctx, bool print_histogram, bool print_fmax, bool p
     }
 }
 
+void get_criticalities(Context *ctx, NetCriticalityMap *net_crit) {
+    CriticalPathMap crit_paths;
+    net_crit->clear();
+    Timing timing(ctx, true, true, &crit_paths, nullptr, net_crit);
+    timing.walk_paths();
+}
+
 NEXTPNR_NAMESPACE_END

common/timing.h

@@ -32,6 +32,19 @@ void assign_budget(Context *ctx, bool quiet = false);
 void timing_analysis(Context *ctx, bool slack_histogram = true, bool print_fmax = true, bool print_path = false,
                      bool warn_on_failure = false);
 
+// Data for the timing optimisation algorithm
+struct NetCriticalityInfo
+{
+    // One each per user
+    std::vector<delay_t> slack;
+    std::vector<float> criticality;
+    unsigned max_path_length = 0;
+    delay_t cd_worst_slack = std::numeric_limits<delay_t>::max();
+};
+
+typedef std::unordered_map<IdString, NetCriticalityInfo> NetCriticalityMap;
+void get_criticalities(Context *ctx, NetCriticalityMap *net_crit);
+
 NEXTPNR_NAMESPACE_END
 
 #endif

common/timing_opt.cc

@@ -23,8 +23,10 @@
  * https://www.cerc.utexas.edu/utda/publications/C205.pdf
  */
 
+#include "timing.h"
 #include "timing_opt.h"
 #include "nextpnr.h"
+#include "util.h"
 NEXTPNR_NAMESPACE_BEGIN
 
 class TimingOptimiser
@@ -37,8 +39,52 @@ class TimingOptimiser
     // Ratio of available to already-candidates to begin borrowing
     const float borrow_thresh = 0.2;
 
-    bool check_cell_delay_limits(CellInfo *cell) {
+    void setup_delay_limits() {
+        for (auto net : sorted(ctx->nets)) {
+            NetInfo *ni = net.second;
+            max_net_delay[ni].clear();
+            max_net_delay[ni].resize(ni->users.size(), std::numeric_limits<delay_t>::max());
+            if (!net_crit.count(net.first))
+                continue;
+            auto &nc = net_crit.at(net.first);
+            if (nc.slack.empty())
+                continue;
+            for (size_t i = 0; i < ni->users.size(); i++) {
+                delay_t net_delay = ctx->getNetinfoRouteDelay(ni, ni->users.at(i));
+                max_net_delay[ni].at(i) = net_delay + ((nc.slack.at(i) - nc.cd_worst_slack) / nc.max_path_length);
+            }
+        }
+    }
 
+    bool check_cell_delay_limits(CellInfo *cell) {
+        for (const auto &port : cell->ports) {
+            int nc;
+            if (ctx->getPortTimingClass(cell, port.first, nc) == TMG_IGNORE)
+                continue;
+            NetInfo *net = port.second.net;
+            if (net == nullptr)
+                continue;
+            if (port.second.type == PORT_IN) {
+                if (net->driver.cell == nullptr || net->driver.cell->bel == BelId())
+                    continue;
+                BelId srcBel = net->driver.cell->bel;
+                if (ctx->estimateDelay(ctx->getBelPinWire(srcBel, net->driver.port),
+                        ctx->getBelPinWire(cell->bel, port.first)) > max_net_delay.at(std::make_pair(cell->name, port.first)))
+                    return false;
+            } else if (port.second.type == PORT_OUT) {
+                for (auto user : net->users) {
+                    // This could get expensive for high-fanout nets??
+                    BelId dstBel = user.cell->bel;
+                    if (dstBel == BelId())
+                        continue;
+                    if (ctx->estimateDelay(ctx->getBelPinWire(cell->bel, port.first),
+                                           ctx->getBelPinWire(dstBel, user.port)) > max_net_delay.at(std::make_pair(user.cell->name, user.port)))
+                        return false;
+                }
+            }
+
+        }
+        return true;
     }
 
     bool acceptable_bel_candidate(CellInfo *cell, BelId newBel) {
@@ -109,8 +155,11 @@ unbind:
     std::vector<IdString> path_cells;
     std::unordered_map<IdString, std::unordered_set<BelId>> cell_neighbour_bels;
     std::unordered_map<BelId, std::unordered_set<IdString>> bel_candidate_cells;
-    // Map net users to net delay limit
-    std::unordered_map<IdString, std::vector<delay_t>> max_net_delay;
+    // Map cell ports to net delay limit
+    std::unordered_map<std::pair<IdString, IdString>, delay_t> max_net_delay;
+    // Criticality data from timing analysis
+    NetCriticalityMap net_crit;
+
     Context *ctx;
 };