ice40: Fix SPRAM model to keep data stable if chipselect is low

According to the official simulation model, and also cross-checked
on real hardware, the data output of the SPRAM when chipselect is
low is kept stable. It doesn't go undefined.

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

diff --git a/techlibs/ice40/cells_sim.v b/techlibs/ice40/cells_sim.v
index 17fe2ec9950ba26278b697dad30478921b57e03b..aa1d7aa863bbae8476e8fc439cb4380e118a1834 100644 (file)
--- a/techlibs/ice40/cells_sim.v
+++ b/techlibs/ice40/cells_sim.v
@@ -2350,16 +2350,19 @@ module SB_SPRAM256KA (
                if (off) begin
                        DATAOUT <= 0;
                end else
-               if (CHIPSELECT && !STANDBY && !WREN) begin
-                       DATAOUT <= mem[ADDRESS];
-               end else begin
-                       if (CHIPSELECT && !STANDBY && WREN) begin
+               if (STANDBY) begin
+                       DATAOUT <= 'bx;
+               end else
+               if (CHIPSELECT) begin
+                       if (!WREN) begin
+                               DATAOUT <= mem[ADDRESS];
+                       end else begin
                                if (MASKWREN[0]) mem[ADDRESS][ 3: 0] = DATAIN[ 3: 0];
                                if (MASKWREN[1]) mem[ADDRESS][ 7: 4] = DATAIN[ 7: 4];
                                if (MASKWREN[2]) mem[ADDRESS][11: 8] = DATAIN[11: 8];
                                if (MASKWREN[3]) mem[ADDRESS][15:12] = DATAIN[15:12];
+                               DATAOUT <= 'bx;
                        end
-                       DATAOUT <= 'bx;
                end
        end
 `endif