Merge branch 'redist_slack' into 'master'

Update budgets throughout placement and routing

See merge request SymbioticEDA/nextpnr!16

1 files changed, 128 insertions, 34 deletions

diff --git a/common/timing.cc b/common/timing.cc
index 4486fc24..2beaeee9 100644
--- a/common/timing.cc
+++ b/common/timing.cc
@@ -22,19 +22,29 @@
 #include <unordered_map>
 #include <utility>
 #include "log.h"
+#include "util.h"
 
 NEXTPNR_NAMESPACE_BEGIN
 
-static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack);
+typedef std::list<const PortRef *> PortRefList;
+
+static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, bool update, delay_t &min_slack,
+                          PortRefList *current_path, PortRefList *crit_path);
 
 // Follow a path, returning budget to annotate
-static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, delay_t slack)
+static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, delay_t slack, bool update,
+                                delay_t &min_slack, PortRefList *current_path, PortRefList *crit_path)
 {
     delay_t value;
     if (ctx->getPortClock(user.cell, user.port) != IdString()) {
         // At the end of a timing path (arguably, should check setup time
         // here too)
         value = slack / path_length;
+        if (slack < min_slack) {
+            min_slack = slack;
+            if (crit_path)
+                *crit_path = *current_path;
+        }
     } else {
         // Default to the path ending here, if no further paths found
         value = slack / path_length;
@@ -47,74 +57,158 @@ static delay_t follow_user_port(Context *ctx, PortRef &user, int path_length, de
                 if (is_path) {
                     NetInfo *net = port.second.net;
                     if (net) {
-                        delay_t path_budget = follow_net(ctx, net, path_length, slack - comb_delay.maxDelay());
+                        delay_t path_budget = follow_net(ctx, net, path_length, slack - comb_delay.maxDelay(), update,
+                                                         min_slack, current_path, crit_path);
                         value = std::min(value, path_budget);
                     }
                 }
             }
         }
     }
-
-    if (value < user.budget) {
-        user.budget = value;
-    }
     return value;
 }
 
-static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack)
+static delay_t follow_net(Context *ctx, NetInfo *net, int path_length, delay_t slack, bool update, delay_t &min_slack,
+                          PortRefList *current_path, PortRefList *crit_path)
 {
     delay_t net_budget = slack / (path_length + 1);
     for (auto &usr : net->users) {
-        net_budget = std::min(net_budget, follow_user_port(ctx, usr, path_length + 1, slack));
+        if (crit_path)
+            current_path->push_back(&usr);
+        // If budget override is less than existing budget, then do not increment path length
+        int pl = path_length + 1;
+        auto budget = ctx->getBudgetOverride(net, usr, net_budget);
+        if (budget < net_budget) {
+            net_budget = budget;
+            pl = std::max(1, path_length);
+        }
+        auto delay = ctx->getNetinfoRouteDelay(net, usr);
+        net_budget = std::min(
+                net_budget, follow_user_port(ctx, usr, pl, slack - delay, update, min_slack, current_path, crit_path));
+        if (update)
+            usr.budget = std::min(usr.budget, delay + net_budget);
+        if (crit_path)
+            current_path->pop_back();
     }
     return net_budget;
 }
 
-void assign_budget(Context *ctx)
+static delay_t walk_paths(Context *ctx, bool update, PortRefList *crit_path)
 {
-    log_break();
-    log_info("Annotating ports with timing budgets\n");
-    // Clear delays to a very high value first
     delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
-    for (auto &net : ctx->nets) {
-        for (auto &usr : net.second->users) {
-            usr.budget = default_slack;
-        }
-    }
-    // Go through all clocked drivers and set up paths
+    delay_t min_slack = default_slack;
+
+    PortRefList current_path;
+
+    // Go through all clocked drivers and distribute the available path
+    //   slack evenly into the budget of every sink on the path
     for (auto &cell : ctx->cells) {
         for (auto port : cell.second->ports) {
             if (port.second.type == PORT_OUT) {
                 IdString clock_domain = ctx->getPortClock(cell.second.get(), port.first);
                 if (clock_domain != IdString()) {
-                    delay_t slack = delay_t(1.0e12 / ctx->target_freq); // TODO: clock constraints
+                    delay_t slack = default_slack; // TODO: clock constraints
                     DelayInfo clkToQ;
                     if (ctx->getCellDelay(cell.second.get(), clock_domain, port.first, clkToQ))
                         slack -= clkToQ.maxDelay();
                     if (port.second.net)
-                        follow_net(ctx, port.second.net, 0, slack);
+                        follow_net(ctx, port.second.net, 0, slack, update, min_slack, &current_path, crit_path);
                 }
             }
         }
     }
 
-    // Post-allocation check
+    return min_slack;
+}
+
+void assign_budget(Context *ctx, bool quiet)
+{
+    if (!quiet) {
+        log_break();
+        log_info("Annotating ports with timing budgets\n");
+    }
+
+    // Clear delays to a very high value first
+    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
     for (auto &net : ctx->nets) {
-        for (auto user : net.second->users) {
-            if (user.budget < 0)
-                log_warning("port %s.%s, connected to net '%s', has negative "
-                            "timing budget of %fns\n",
-                            user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
-                            ctx->getDelayNS(user.budget));
-            if (ctx->verbose)
-                log_info("port %s.%s, connected to net '%s', has "
-                         "timing budget of %fns\n",
-                         user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
-                         ctx->getDelayNS(user.budget));
+        for (auto &usr : net.second->users) {
+            usr.budget = default_slack;
+        }
+    }
+
+    delay_t min_slack = walk_paths(ctx, true, nullptr);
+
+    if (!quiet || ctx->verbose) {
+        for (auto &net : ctx->nets) {
+            for (auto &user : net.second->users) {
+                // Post-update check
+                if (ctx->user_freq && user.budget < 0)
+                    log_warning("port %s.%s, connected to net '%s', has negative "
+                                "timing budget of %fns\n",
+                                user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
+                                ctx->getDelayNS(user.budget));
+                else if (ctx->verbose)
+                    log_info("port %s.%s, connected to net '%s', has "
+                             "timing budget of %fns\n",
+                             user.cell->name.c_str(ctx), user.port.c_str(ctx), net.first.c_str(ctx),
+                             ctx->getDelayNS(user.budget));
+            }
         }
     }
 
-    log_info("Checksum: 0x%08x\n", ctx->checksum());
+    // For slack redistribution, if user has not specified a frequency
+    //   dynamically adjust the target frequency to be the currently
+    //   achieved maximum
+    if (!ctx->user_freq && ctx->slack_redist_iter > 0) {
+        ctx->target_freq = 1e12 / (default_slack - min_slack);
+        /*if (ctx->verbose)*/
+        log_info("minimum slack for this assign = %d, target Fmax for next update = %.2f MHz\n", min_slack,
+                 ctx->target_freq / 1e6);
+    }
+
+    if (!quiet)
+        log_info("Checksum: 0x%08x\n", ctx->checksum());
+}
+
+delay_t timing_analysis(Context *ctx, bool print_fmax, bool print_path)
+{
+    delay_t default_slack = delay_t(1.0e12 / ctx->target_freq);
+    PortRefList crit_path;
+    delay_t min_slack = walk_paths(ctx, false, &crit_path);
+    if (print_path) {
+        delay_t total = 0;
+        log_break();
+        log_info("Critical path report:\n");
+        log_info("curr total\n");
+        auto &front = crit_path.front();
+        auto &front_port = front->cell->ports.at(front->port);
+        auto &front_driver = front_port.net->driver;
+        auto last_port = ctx->getPortClock(front_driver.cell, front_driver.port);
+        for (auto sink : crit_path) {
+            auto sink_cell = sink->cell;
+            auto &port = sink_cell->ports.at(sink->port);
+            auto net = port.net;
+            auto &driver = net->driver;
+            auto driver_cell = driver.cell;
+            DelayInfo comb_delay;
+            ctx->getCellDelay(sink_cell, last_port, driver.port, comb_delay);
+            total += comb_delay.maxDelay();
+            log_info("%4d %4d  Source %s.%s\n", comb_delay.maxDelay(), total, driver_cell->name.c_str(ctx),
+                     driver.port.c_str(ctx));
+            auto net_delay = ctx->getNetinfoRouteDelay(net, *sink);
+            total += net_delay;
+            auto driver_loc = ctx->getBelLocation(driver_cell->bel);
+            auto sink_loc = ctx->getBelLocation(sink_cell->bel);
+            log_info("%4d %4d    Net %s budget %d (%d,%d) -> (%d,%d)\n", net_delay, total, net->name.c_str(ctx),
+                     sink->budget, driver_loc.x, driver_loc.y, sink_loc.x, sink_loc.y);
+            log_info("                Sink %s.%s\n", sink_cell->name.c_str(ctx), sink->port.c_str(ctx));
+            last_port = sink->port;
+        }
+        log_break();
+    }
+    if (print_fmax)
+        log_info("estimated Fmax = %.2f MHz\n", 1e6 / (default_slack - min_slack));
+    return min_slack;
 }
 
 NEXTPNR_NAMESPACE_END