ice40: Introduce the concept of forPadIn SB_GB

Those are cells that are created mainly to handle the various sources a
global network can be driven from other than a user net.

When the flag is set, this means the global network usually driven by
this BEL is in fact driven by something else and so that SB_GB BEL and
matching global network can't be used.

This is also what gets used to set the extra bits during bitstream
generation.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/ice40/arch.cc b/ice40/arch.cc
index 995150ac..3138b813 100644
--- a/ice40/arch.cc
+++ b/ice40/arch.cc
@@ -1044,6 +1044,8 @@ void Arch::assignCellInfo(CellInfo *cell)
             cell->lcInfo.inputCount++;
     } else if (cell->type == id_SB_IO) {
         cell->ioInfo.lvds = str_or_default(cell->params, id_IO_STANDARD, "SB_LVCMOS") == "SB_LVDS_INPUT";
+    } else if (cell->type == id_SB_GB) {
+        cell->gbInfo.forPadIn = bool_or_default(cell->attrs, this->id("FOR_PAD_IN"));
     }
 }