ice40: Rework pull-up attribute copy to SB_IO blocks

We try to copy the attribute only when there is a chance for
the output driver to not be active.

Note that this can _also_ happen when a port is specified as
output but has a TBUF, which the previous code wasn't handling.

We could copy the attribute "all-the-time" but this would
mean if a user specified a `-pullup yes` in the PCF for a
permanently driven output pin, we'd be burning power for
nothing.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/ice40/cells.cc b/ice40/cells.cc
index fc24caaf..5e3bd139 100644
--- a/ice40/cells.cc
+++ b/ice40/cells.cc
@@ -404,25 +404,23 @@ void dff_to_lc(const Context *ctx, CellInfo *dff, CellInfo *lc, bool pass_thru_l
 
 void nxio_to_sb(Context *ctx, CellInfo *nxio, CellInfo *sbio, pool<IdString> &todelete_cells)
 {
+    bool pull_up_attr = false;
+
     if (nxio->type == ctx->id("$nextpnr_ibuf")) {
         sbio->params[id_PIN_TYPE] = 1;
-        auto pu_attr = nxio->attrs.find(id_PULLUP);
-        if (pu_attr != nxio->attrs.end())
-            sbio->params[id_PULLUP] = pu_attr->second;
         nxio->movePortTo(id_O, sbio, id_D_IN_0);
+        pull_up_attr = true;
     } else if (nxio->type == ctx->id("$nextpnr_obuf")) {
         sbio->params[id_PIN_TYPE] = 25;
         nxio->movePortTo(id_I, sbio, id_D_OUT_0);
     } else if (nxio->type == ctx->id("$nextpnr_iobuf")) {
         // N.B. tristate will be dealt with below
         NetInfo *i = nxio->getPort(id_I);
-        if (i == nullptr || i->driver.cell == nullptr)
+        if (i == nullptr || i->driver.cell == nullptr) {
             sbio->params[id_PIN_TYPE] = 1;
-        else
+            pull_up_attr = true;
+        } else
             sbio->params[id_PIN_TYPE] = 25;
-        auto pu_attr = nxio->attrs.find(id_PULLUP);
-        if (pu_attr != nxio->attrs.end())
-            sbio->params[id_PULLUP] = pu_attr->second;
         nxio->movePortTo(id_I, sbio, id_D_OUT_0);
         nxio->movePortTo(id_O, sbio, id_D_IN_0);
     } else {
@@ -465,6 +463,7 @@ void nxio_to_sb(Context *ctx, CellInfo *nxio, CellInfo *sbio, pool<IdString> &to
         sbio->params[id_PIN_TYPE] = 41;
         tbuf->movePortTo(id_A, sbio, id_D_OUT_0);
         tbuf->movePortTo(id_E, sbio, id_OUTPUT_ENABLE);
+        pull_up_attr = true;
 
         if (donet->users.entries() > 1) {
             for (auto user : donet->users)
@@ -476,6 +475,13 @@ void nxio_to_sb(Context *ctx, CellInfo *nxio, CellInfo *sbio, pool<IdString> &to
         ctx->nets.erase(donet->name);
         todelete_cells.insert(tbuf->name);
     }
+
+    // Copy pull-up attribute if there's any chance output driver isn't active
+    if (pull_up_attr) {
+        auto pu_attr = nxio->attrs.find(id_PULLUP);
+        if (pu_attr != nxio->attrs.end())
+            sbio->params[id_PULLUP] = pu_attr->second;
+    }
 }
 
 uint8_t sb_pll40_type(const BaseCtx *ctx, const CellInfo *cell)