[otbn,rtl] Only signal "done" when we were actually running
The done_o output is used in otbn.sv as an interrupt and also gates us
updating the ERR_BITS external CSR. In both cases, we don't want it to
go high if we weren't already running something.
Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/hw/ip/otbn/rtl/otbn_controller.sv b/hw/ip/otbn/rtl/otbn_controller.sv
index 13c54a2..f691743 100644
--- a/hw/ip/otbn/rtl/otbn_controller.sv
+++ b/hw/ip/otbn/rtl/otbn_controller.sv
@@ -133,6 +133,7 @@
logic err;
logic fatal_err;
logic done_complete;
+ logic executing;
logic insn_fetch_req_valid_raw;
@@ -228,11 +229,18 @@
assign stall = mem_stall | ispr_stall;
- // OTBN is done (raising the 'done' interrupt) either when it executes an ecall or an error
- // occurs. The ecall triggered done is factored out as `done_complete` to avoid logic loops in the
- // error handling logic.
+ // OTBN is done when it was executing something (in state OtbnStateUrndRefresh, OtbnStateRun or
+ // OtbnStateStall) and either it executes an ecall or an error occurs. A pulse on the done signal
+ // raises the 'done' interrupt and also tells the top-level to update its err_bits status
+ // register.
+ //
+ // The calculation that ecall triggered done is factored out as `done_complete` to avoid logic
+ // loops in the error handling logic.
assign done_complete = (insn_valid_i && insn_dec_shared_i.ecall_insn);
- assign done_o = done_complete | err;
+ assign executing = (state_q == OtbnStateUrndRefresh) ||
+ (state_q == OtbnStateRun) ||
+ (state_q == OtbnStateStall);
+ assign done_o = executing & (done_complete | err);
assign locked_o = state_q == OtbnStateLocked;
assign jump_or_branch = (insn_valid_i &
