[ECO] prim_count.sv CDC

[moidx]

Description

Reported by: @meisnere

sw_alert_handler_ping_ok test fails post synthesis.

The root cause seems to point to glitches on err_o. This is a CDC error as it takes time for the sum to converge here:

opentitan/hw/ip/prim/rtl/prim_count.sv

Lines 140 to 143 in e439226

	// The sum of both counters must always equal the counter maximum.
	logic [Width:0] sum;
	assign sum = (cnt_q[0] + cnt_q[1]);
	assign err_o = (sum != {1'b0, {Width{1'b1}}});

CC @andreaskurth @vogelpi

[vogelpi]

Thanks for creating the issue for this here @moidx . I've just created a PR to fix this #24121 and we're discussing with the PD team to assess if this can still be absorbed as ECO.

[vogelpi]

Update: it has been decided to take a more holistic approach and fix all prim_count instances + the prim_esc_receiver instances:

• [prim_count] Register err_o to avoid potential CDC issues downstream #24125
• [prim_esc_receiver] Register esc_req_o to avoid potential CDC issues #24127

[vogelpi]

I am again closing this issue as the corresponding PRs #24125 and #24127 got both merged.