axi_demux: Add parameter AtopSupport

Adapted from `0009-Remove-atomics-from-DMA-path.patch` of the Snitch
repository.

Co-authored-by: Florian Zaruba <[email protected]>

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## Unreleased
 
 ### Added
+- `axi_demux`: Add parameter `AtopSupport` to optionally disable the support for atomic operations
+  (ATOPs).  This parameter defaults to `1'b1`, i.e., ATOPs are supported.  Therefore, this change is
+  backward-compatible.
 - `axi_xbar`: Add `Connectivity` parameter to enable the implementation of partially-connected
   crossbars.  This parameter defaults to `'1`, i.e., every slave port is connected to every master
   port.  Therefore, this change is backward-compatible.

src/axi_demux.sv

@@ -12,6 +12,7 @@
 // - Wolfgang Roenninger <[email protected]>
 // - Andreas Kurth <[email protected]>
 
+`include "common_cells/assertions.svh"
 `include "common_cells/registers.svh"
 
 `ifdef QUESTA
@@ -24,6 +25,7 @@
 // See `doc/axi_demux.md` for the documentation, including the definition of parameters and ports.
 module axi_demux #(
   parameter int unsigned AxiIdWidth     = 32'd0,
+  parameter bit          AtopSupport    = 1'b1,
   parameter type         aw_chan_t      = logic,
   parameter type         w_chan_t       = logic,
   parameter type         b_chan_t       = logic,
@@ -205,12 +207,14 @@ module axi_demux #(
           slv_aw_ready    = 1'b1;
           lock_aw_valid_d = 1'b0;
           load_aw_lock    = 1'b1;
-          atop_inject     = slv_aw_chan_select.aw_chan.atop[5]; // inject the ATOP if necessary
+          // inject the ATOP if necessary
+          atop_inject     = slv_aw_chan_select.aw_chan.atop[5] & AtopSupport;
         end
       end else begin
         // Process can start handling a transaction if its `i_aw_id_counter` and `w_fifo` have
-        // space in them. Further check if we could inject something on the AR channel.
-        if (!aw_id_cnt_full && !w_fifo_full && !ar_id_cnt_full) begin
+        // space in them. Further check if we could inject something on the AR channel (only if
+        // ATOPs are supported).
+        if (!aw_id_cnt_full && !w_fifo_full && (!ar_id_cnt_full || !AtopSupport)) begin
           // there is a valid AW vector make the id lookup and go further, if it passes
           if (slv_aw_valid && (!aw_select_occupied ||
              (slv_aw_chan_select.aw_select == lookup_aw_select))) begin
@@ -221,7 +225,7 @@ module axi_demux #(
             // on AW transaction
             if (aw_ready) begin
               slv_aw_ready = 1'b1;
-              atop_inject  = slv_aw_chan_select.aw_chan.atop[5];
+              atop_inject  = slv_aw_chan_select.aw_chan.atop[5] & AtopSupport;
             // no AW transaction this cycle, lock the decision
             end else begin
               lock_aw_valid_d = 1'b1;
@@ -574,6 +578,7 @@ module axi_demux #(
     internal_aw_select: assert property( @(posedge clk_i)
         (aw_valid |-> slv_aw_chan_select.aw_select < NoMstPorts))
       else $fatal(1, "slv_aw_chan_select.aw_select illegal while aw_valid.");
+    `ASSUME(NoAtopAllowed, !AtopSupport && slv_req_i.aw_valid |-> slv_req_i.aw.atop == '0)
 `endif
 `endif
 // pragma translate_on

src/axi_xbar.sv

@@ -152,6 +152,7 @@ import cf_math_pkg::idx_width;
     // pragma translate_on
     axi_demux #(
       .AxiIdWidth     ( Cfg.AxiIdWidthSlvPorts ),  // ID Width
+      .AtopSupport    ( ATOPs                  ),
       .aw_chan_t      ( slv_aw_chan_t          ),  // AW Channel Type
       .w_chan_t       ( w_chan_t               ),  //  W Channel Type
       .b_chan_t       ( slv_b_chan_t           ),  //  B Channel Type