ice40: Promote reset signal

Signed-off-by: David Shah <davey1576@gmail.com>

5 files changed, 89 insertions, 36 deletions

diff --git a/common/place.cc b/common/place.cc
index dfca313f..a6d3040f 100644
--- a/common/place.cc
+++ b/common/place.cc
@@ -122,7 +122,8 @@ static float get_wirelength(Chip *chip, NetInfo *net)
         return 0;
     consider_driver =
             chip->estimatePosition(driver_cell->bel, driver_x, driver_y);
-    WireId drv_wire = chip->getWireBelPin(driver_cell->bel, portPinFromId(net->driver.port));
+    WireId drv_wire = chip->getWireBelPin(driver_cell->bel,
+                                          portPinFromId(net->driver.port));
     if (!consider_driver)
         return 0;
     for (auto load : net->users) {
@@ -132,9 +133,11 @@ static float get_wirelength(Chip *chip, NetInfo *net)
         int load_x = 0, load_y = 0;
         if (load_cell->bel == BelId())
             continue;
-        //chip->estimatePosition(load_cell->bel, load_x, load_y);
-        WireId user_wire = chip->getWireBelPin(load_cell->bel, portPinFromId(load.port));
-        //wirelength += std::abs(load_x - driver_x) + std::abs(load_y - driver_y);
+        // chip->estimatePosition(load_cell->bel, load_x, load_y);
+        WireId user_wire =
+                chip->getWireBelPin(load_cell->bel, portPinFromId(load.port));
+        // wirelength += std::abs(load_x - driver_x) + std::abs(load_y -
+        // driver_y);
         wirelength += chip->estimateDelay(drv_wire, user_wire);
     }
     return wirelength;
diff --git a/ice40/arch_place.cc b/ice40/arch_place.cc
index 492ed846..19c95816 100644
--- a/ice40/arch_place.cc
+++ b/ice40/arch_place.cc
@@ -99,6 +99,20 @@ bool isValidBelForCell(Design *design, CellInfo *cell, BelId bel)
         return logicCellsCompatible(cells);
     } else if (cell->type == "SB_IO") {
         return design->chip.getBelPackagePin(bel) != "";
+    } else if (cell->type == "SB_GB") {
+        bool is_reset = false, is_cen = false;
+        assert(cell->ports.at("GLOBAL_BUFFER_OUTPUT").net != nullptr);
+        for (auto user : cell->ports.at("GLOBAL_BUFFER_OUTPUT").net->users) {
+            if (is_reset_port(user))
+                is_reset = true;
+        }
+        IdString glb_net = chip.getWireName(
+                chip.getWireBelPin(bel, PIN_GLOBAL_BUFFER_OUTPUT));
+        int glb_id = std::stoi(std::string("") + glb_net.str().back());
+        if (is_reset)
+            return (glb_id % 2) == 0;
+        else
+            return true;
     } else {
         // TODO: IO cell clock checks
         return true;
diff --git a/ice40/cells.cc b/ice40/cells.cc
index 61b24ce3..52356711 100644
--- a/ice40/cells.cc
+++ b/ice40/cells.cc
@@ -190,6 +190,26 @@ void nxio_to_sb(CellInfo *nxio, CellInfo *sbio)
     }
 }
 
+bool is_clock_port(const PortRef &port)
+{
+    if (port.cell == nullptr)
+        return false;
+    if (is_ff(port.cell))
+        return port.port == "C";
+    if (is_ram(port.cell))
+        return port.port == "RCLK" || port.port == "WCLK";
+    return false;
+}
+
+bool is_reset_port(const PortRef &port)
+{
+    if (port.cell == nullptr)
+        return false;
+    if (is_ff(port.cell))
+        return port.port == "R" || port.port == "S";
+    return false;
+}
+
 bool is_global_net(const NetInfo *net)
 {
     return bool(net_driven_by(net, is_gbuf, "GLOBAL_BUFFER_OUTPUT"));
diff --git a/ice40/cells.h b/ice40/cells.h
index a2fa4c16..f1bc5d1f 100644
--- a/ice40/cells.h
+++ b/ice40/cells.h
@@ -77,6 +77,12 @@ void nxio_to_sb(CellInfo *nxio, CellInfo *sbio);
 // Return true if a net is a global net
 bool is_global_net(const NetInfo *net);
 
+// Return true if a port is a clock port
+bool is_clock_port(const PortRef &port);
+
+// Return true if a port is a reset port
+bool is_reset_port(const PortRef &port);
+
 NEXTPNR_NAMESPACE_END
 
 #endif
diff --git a/ice40/pack.cc b/ice40/pack.cc
index e045c05c..d88870e0 100644
--- a/ice40/pack.cc
+++ b/ice40/pack.cc
@@ -276,15 +276,34 @@ static void pack_io(Design *design)
     }
 }
 
-static bool is_clock_port(const PortRef &port)
+static void insert_global(Design *design, NetInfo *net, bool is_reset,
+                          bool is_cen)
 {
-    if (port.cell == nullptr)
-        return false;
-    if (is_ff(port.cell))
-        return port.port == "C";
-    if (is_ram(port.cell))
-        return port.port == "RCLK" || port.port == "WCLK";
-    return false;
+    CellInfo *gb = create_ice_cell(design, "SB_GB");
+    gb->ports["USER_SIGNAL_TO_GLOBAL_BUFFER"].net = net;
+    PortRef pr;
+    pr.cell = gb;
+    pr.port = "USER_SIGNAL_TO_GLOBAL_BUFFER";
+    net->users.push_back(pr);
+
+    pr.cell = gb;
+    pr.port = "GLOBAL_BUFFER_OUTPUT";
+    NetInfo *glbnet = new NetInfo();
+    glbnet->name = net->name.str() + "_glb";
+    glbnet->driver = pr;
+    design->nets[glbnet->name] = glbnet;
+    gb->ports["GLOBAL_BUFFER_OUTPUT"].net = glbnet;
+    std::vector<PortRef> keep_users;
+    for (auto user : net->users) {
+        if (is_clock_port(user) || (is_reset && is_reset_port(user))) {
+            user.cell->ports[user.port].net = glbnet;
+            glbnet->users.push_back(user);
+        } else {
+            keep_users.push_back(user);
+        }
+    }
+    net->users = keep_users;
+    design->cells[gb->name] = gb;
 }
 
 // Simple global promoter (clock only)
@@ -293,13 +312,18 @@ static void promote_globals(Design *design)
     log_info("Promoting globals..\n");
 
     std::unordered_map<IdString, int> clock_count;
+    std::unordered_map<IdString, int> reset_count;
+
     for (auto net : design->nets) {
         NetInfo *ni = net.second;
         if (ni->driver.cell != nullptr && !is_global_net(ni)) {
             clock_count[net.first] = 0;
+            reset_count[net.first] = 0;
             for (auto user : ni->users) {
                 if (is_clock_port(user))
                     clock_count[net.first]++;
+                if (is_reset_port(user))
+                    reset_count[net.first]++;
             }
         }
     }
@@ -310,30 +334,16 @@ static void promote_globals(Design *design)
                                          });
     if (global_clock->second > 0) {
         NetInfo *clknet = design->nets[global_clock->first];
-        CellInfo *gb = create_ice_cell(design, "SB_GB");
-        gb->ports["USER_SIGNAL_TO_GLOBAL_BUFFER"].net = clknet;
-        PortRef pr;
-        pr.cell = gb;
-        pr.port = "USER_SIGNAL_TO_GLOBAL_BUFFER";
-        clknet->users.push_back(pr);
-
-        pr.cell = gb;
-        pr.port = "GLOBAL_BUFFER_OUTPUT";
-        NetInfo *glbnet = new NetInfo();
-        glbnet->name = clknet->name.str() + "_glb";
-        glbnet->driver = pr;
-        design->nets[glbnet->name] = glbnet;
-        std::vector<PortRef> keep_users;
-        for (auto user : clknet->users) {
-            if (is_clock_port(user)) {
-                user.cell->ports[user.port].net = glbnet;
-                glbnet->users.push_back(user);
-            } else {
-                keep_users.push_back(user);
-            }
-        }
-        clknet->users = keep_users;
-        design->cells[gb->name] = gb;
+        insert_global(design, clknet, false, false);
+    }
+    auto global_reset = std::max_element(reset_count.begin(), reset_count.end(),
+                                         [](const std::pair<IdString, int> &a,
+                                            const std::pair<IdString, int> &b) {
+                                             return a.second < b.second;
+                                         });
+    if (global_reset->second > 0) {
+        NetInfo *rstnet = design->nets[global_reset->first];
+        insert_global(design, rstnet, true, false);
     }
 }