[otbn, rtl] Add buffer for rf_bignum.intg_err_o signal.
This is done so Yosys do not optimize this signal in the
netlist. We are excluding this signal from formal masking
analysis.
Signed-off-by: Abdullah Varici <abdullah.varici@lowrisc.org>
diff --git a/hw/ip/otbn/rtl/otbn_rf_bignum.sv b/hw/ip/otbn/rtl/otbn_rf_bignum.sv
index fa55726..4d728a0 100644
--- a/hw/ip/otbn/rtl/otbn_rf_bignum.sv
+++ b/hw/ip/otbn/rtl/otbn_rf_bignum.sv
@@ -160,8 +160,21 @@
);
end
- assign intg_err_o = ((|rd_data_a_err) & rd_en_a_i) |
- ((|rd_data_b_err) & rd_en_b_i);
+ logic intg_err_unbuf, intg_err_buf;
+
+ assign intg_err_unbuf = ((|rd_data_a_err) & rd_en_a_i) |
+ ((|rd_data_b_err) & rd_en_b_i);
+
+ // This primitive is used to place a constraint for synthesis. It is required to
+ // ensure that the signal name will be available in the synthesized netlist.
+ prim_buf #(
+ .Width(1)
+ ) u_prim_buf (
+ .in_i(intg_err_unbuf),
+ .out_o(intg_err_buf)
+ );
+
+ assign intg_err_o = intg_err_buf;
`ASSERT(BlankingBignumRegReadA_A,
!rd_en_a_i |-> rd_data_a_intg_o == '0,
