[otp_ctrl] Make sure KDI observes EDN req/ack protocol at all times
Fix #6605
Signed-off-by: Michael Schaffner <msf@opentitan.org>
diff --git a/hw/ip/otp_ctrl/rtl/otp_ctrl_kdi.sv b/hw/ip/otp_ctrl/rtl/otp_ctrl_kdi.sv
index 940f242..70396a5 100644
--- a/hw/ip/otp_ctrl/rtl/otp_ctrl_kdi.sv
+++ b/hw/ip/otp_ctrl/rtl/otp_ctrl_kdi.sv
@@ -276,6 +276,9 @@
state_e state_d, state_q;
+ logic edn_req_d, edn_req_q;
+ assign edn_req_o = edn_req_q;
+
always_comb begin : p_fsm
state_d = state_q;
@@ -288,8 +291,12 @@
entropy_cnt_en = 1'b0;
entropy_cnt_clr = 1'b0;
- // EDN 128bit block fetch request
- edn_req_o = 1'b0;
+ // EDN 128bit block fetch request.
+ // This keeps the request alive until it has
+ // been acked to adhere to the req/ack protocol
+ // even in cases where the FSM jumps into
+ // an error state while waiting for a request.
+ edn_req_d = edn_req_q & ~edn_ack_i;
// Data selection and temp registers
data_sel = SeedData;
@@ -362,7 +369,7 @@
// Fetch random data to ingest for key derivation.
FetchEntropySt: begin
scrmbl_mtx_req_o = 1'b1;
- edn_req_o = 1'b1;
+ edn_req_d = 1'b1;
if (edn_ack_i) begin
nonce_reg_en = 1'b1;
// Finished, go and acknowledge this request.
@@ -442,7 +449,7 @@
// Fetch additional nonce data. Note that the mutex is released in
// this state.
FetchNonceSt: begin
- edn_req_o = 1'b1;
+ edn_req_d = 1'b1;
if (edn_ack_i) begin
nonce_reg_en = 1'b1;
// Finished, go and acknowledge this request.
@@ -506,12 +513,14 @@
key_out_q <= '0;
nonce_out_q <= '0;
seed_valid_q <= 1'b0;
+ edn_req_q <= 1'b0;
end else begin
seed_cnt_q <= seed_cnt_d;
entropy_cnt_q <= entropy_cnt_d;
key_out_q <= key_out_d;
nonce_out_q <= nonce_out_d;
seed_valid_q <= seed_valid_d;
+ edn_req_q <= edn_req_d;
end
end
