fix(kmac): Not advance the ErrChk FSM in error cases
_Related Issue: https://github.com/lowRISC/opentitan/issues/14470 _
The `kmac_errchk` module reports errors in case of SW's mis-config/
mis-control. When the module detects any errors, `kmac_errchk` blocks
the SW command and report via **ERR_CODE**.
However, the module has advanced to the next state internally. The
internal FSM inside the `kmac_errchk` is to track the external and check
the correctness.
In this commit, the `kmac_errchk` stops moving to the next state in case
of `block_swcmd` occurs.
It is best to add the block condition in the `always_ff` of the `st`.
However, the sparse FSM coding style prevents it from adding the latch
enable condition. The issue
https://github.com/lowRISC/opentitan/issues/14631 has been created to
enhance the macro and the flop module.
Signed-off-by: Eunchan Kim <eunchan@opentitan.org>
diff --git a/hw/ip/kmac/rtl/kmac_errchk.sv b/hw/ip/kmac/rtl/kmac_errchk.sv
index bfbd481..78c66c3 100644
--- a/hw/ip/kmac/rtl/kmac_errchk.sv
+++ b/hw/ip/kmac/rtl/kmac_errchk.sv
@@ -322,7 +322,17 @@
///////////////////
// State Machine //
///////////////////
- `PRIM_FLOP_SPARSE_FSM(u_state_regs, st_d, st, st_e, StIdle)
+ st_e st_gated_d;
+
+ `PRIM_FLOP_SPARSE_FSM(u_state_regs, st_gated_d, st, st_e, StIdle)
+
+ // ICEBOX(#14631): Move block_swcmd to PRIM_FLOP_SPARSE_FSM()
+ //
+ // It would be better to place this condition (block_swcmd) in `always_ff`
+ // block to clearly indicate the clock gating condition. However, the
+ // statemachine uses the sparse encoding scheme and macro. It prevents any
+ // latch enable signals.
+ assign st_gated_d = (block_swcmd) ? st : st_d ;
always_comb begin : next_state
st_d = st;
