commit ec81414ee206d73d50902a680316e67ee1a3b01d
author Joshua Park <jeoong@google.com> Wed Aug 03 09:42:03 2022 -0700
committer tjaychen <timothytim@google.com> Thu Sep 08 16:24:21 2022 -0700
tree 63b2d2bc0052211309042b71988fe9dcc01aee6a
parent bd23a1439ac86a0261a489f125071167cbc62655

[CDC/PRIM] Updated prim_fifo_sync and prim_fifo_async to avoid CDC in rdata

- rdata_o is qualified with rvalid_o to avoid being used when rvalid_o is 0
- This CDC error is found in #13834

Signed-off-by: Joshua Park <jeoong@google.com>

Reverted back prim_fifo_sync to reduce area increase

Added OutputZeroIfInvalid to support read domain qualification

hw/ip/prim/rtl/prim_fifo_async.sv

diff --git a/hw/ip/prim/rtl/prim_fifo_async.sv b/hw/ip/prim/rtl/prim_fifo_async.sv
index e2f2d07..0edebc7 100644
--- a/hw/ip/prim/rtl/prim_fifo_async.sv
+++ b/hw/ip/prim/rtl/prim_fifo_async.sv
@@ -10,6 +10,7 @@
   parameter  int unsigned Width  = 16,
   parameter  int unsigned Depth  = 4,
   parameter  bit OutputZeroIfEmpty = 1'b0, // if == 1 always output 0 when FIFO is empty
+  parameter  bit OutputZeroIfInvalid = 1'b0, // if == 1 always output 0 when rvalid_o is low
   localparam int unsigned DepthW = $clog2(Depth+1) // derived parameter representing [0..Depth]
 ) (
   // write port
@@ -197,10 +198,21 @@
 
   end
 
+  // rdata_o is qualified with rvalid_o to avoid CDC error
   if (OutputZeroIfEmpty == 1'b1) begin : gen_output_zero
-    assign rdata_o = empty_rclk ? '0 : rdata_int;
+    if (OutputZeroIfInvalid  == 1'b1) begin : gen_invalid_zero
+      assign rdata_o = empty_rclk ? '0 : (rvalid_o ? rdata_int : '0);
+    end
+    else begin : gen_invalid_non_zero
+      assign rdata_o = empty_rclk ? '0 : rdata_int;
+    end
   end else begin : gen_no_output_zero
-    assign rdata_o = rdata_int;
+    if (OutputZeroIfInvalid  == 1'b1) begin : gen_invalid_zero
+        assign rdata_o = rvalid_o ? rdata_int : '0;
+    end
+    else begin : gen_invalid_non_zero
+        assign rdata_o = rdata_int;
+    end
   end
 
   //////////////////////////////////////

hw/ip/tlul/rtl/tlul_fifo_async.sv

diff --git a/hw/ip/tlul/rtl/tlul_fifo_async.sv b/hw/ip/tlul/rtl/tlul_fifo_async.sv
index fd0958c..d40d414 100644
--- a/hw/ip/tlul/rtl/tlul_fifo_async.sv
+++ b/hw/ip/tlul/rtl/tlul_fifo_async.sv
@@ -25,7 +25,11 @@
   // Put everything on the request side into one FIFO
   localparam int unsigned REQFIFO_WIDTH = $bits(tlul_pkg::tl_h2d_t)-2;
 
-  prim_fifo_async #(.Width(REQFIFO_WIDTH), .Depth(ReqDepth)) reqfifo (
+  prim_fifo_async #(
+    .Width(REQFIFO_WIDTH),
+    .Depth(ReqDepth),
+    .OutputZeroIfInvalid(1)
+  ) reqfifo (
     .clk_wr_i      (clk_h_i),
     .rst_wr_ni     (rst_h_ni),
     .clk_rd_i      (clk_d_i),
@@ -58,7 +62,11 @@
 
   localparam int unsigned RSPFIFO_WIDTH = $bits(tlul_pkg::tl_d2h_t) -2;
 
-  prim_fifo_async #(.Width(RSPFIFO_WIDTH), .Depth(RspDepth)) rspfifo (
+  prim_fifo_async #(
+    .Width(RSPFIFO_WIDTH),
+    .Depth(RspDepth),
+    .OutputZeroIfInvalid(1)
+  ) rspfifo (
     .clk_wr_i      (clk_d_i),
     .rst_wr_ni     (rst_d_ni),
     .clk_rd_i      (clk_h_i),