hdl/sim: Protect CIWBMasterAccessor against multiple requests

When performing reads/writes from multiple threads, CIWBMasterAccessor does not provide any protection, leading to data from one request being delivered to another. By replacing the data queues with SV mailboxes, we ensure that only one thread can access the mailbox at any given time. Furthermore, we add a SV event in wb_cycle_t, which is used to notify the readm()/writem() tasks that their transfer is complete, to avoid getting the result of the wrong transfer.

hdl/sim: Protect CIWBMasterAccessor against multiple requests
When performing reads/writes from multiple threads, CIWBMasterAccessor does not provide any protection, leading to data from one request being delivered to another. By replacing the data queues with SV mailboxes, we ensure that only one thread can access the mailbox at any given time. Furthermore, we add a SV event in wb_cycle_t, which is used to notify the readm()/writem() tasks that their transfer is complete, to avoid getting the result of the wrong transfer.
e85a2855 · Dimitris Lampridis · 17140a58 · e85a2855 · e85a2855 · e85a2855
Commit e85a2855 authored Jul 14, 2022 by Dimitris Lampridis
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Showing with 38 additions and 29 deletions

if_wb_master.svh sim/if_wb_master.svh +30 -28

if_wishbone_accessor.svh sim/if_wishbone_accessor.svh +7 -1

if_wishbone_types.svh sim/if_wishbone_types.svh +1 -0

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--- a/sim/if_wb_master.svh
+++ b/sim/if_wb_master.svh
@@ -72,8 +72,8 @@ interface IWishboneMaster
         WAIT_ACK
   } xf_state;

-   wb_cycle_t request_queue[$];
-   wb_cycle_t result_queue[$];
+   mailbox #(wb_cycle_t) request_queue;
+   mailbox #(wb_cycle_t) result_queue;

   struct {
      int gen_random_throttling;
@@ -283,35 +283,29 @@ class CIWBMasterAccessor extends CWishboneAccessor;
   endfunction // poll

   task get(ref wb_cycle_t xfer);
-      while(!result_queue.size())
-        @(posedge clk_i);
-      xfer = result_queue.pop_front();
+      result_queue.get(xfer);
   endtask // get

   task put(ref wb_cycle_t xfer);
-      request_queue.push_back(xfer);
+      request_queue.put(xfer);
   endtask // put

   function int idle();
-      return (request_queue.size() == 0) && (xf_state == IDLE);
+      return (request_queue.num() == 0) && (xf_state == IDLE);
   endfunction // idle

 endclass // CIWBMasterAccessor

-
   CIWBMasterAccessor theAccessor;

-   initial
-     theAccessor = new;
-   
   function automatic CIWBMasterAccessor get_accessor();
      return theAccessor;
   endfunction // get_accessor

   always@(posedge clk_i)
     if (!rst_n_i) begin
-        request_queue = {};
-        result_queue  = {};
+        request_queue = new();
+        result_queue  = new();
        xf_state      = IDLE;
        cyc          <= 0;
        dat_o        <= 0;
@@ -322,30 +316,38 @@ endclass // CIWBMasterAccessor
  end

   initial begin
+      theAccessor   = new;
+      request_queue = new();
+      result_queue  = new();
+
      settings.gen_random_throttling  = 0;
      settings.throttle_prob          = 0.1;
      settings.addr_gran              = WORD;
-   end
-
-   initial forever begin
-      @(posedge clk_i);

-      if (request_queue.size() > 0) begin
+      forever begin

         wb_cycle_t c;

-         c = request_queue.pop_front();
+         @(posedge clk_i);

-         case(c.ctype)
-           PIPELINED:
-             pipelined_cycle(c);
-           CLASSIC:
-             classic_cycle(c);
-         endcase
+         if (request_queue.try_get(c)) begin

-         result_queue.push_back(c);
-      end
+            case (c.ctype)
+              PIPELINED:
+                pipelined_cycle(c);
+              CLASSIC:
+                classic_cycle(c);
+            endcase
+
+            // Notify any waiting thread that the transfer is complete
+            ->c.done;
+
+            result_queue.put(c);
+
+         end // if (request_queue.try_get(c))
+
+      end // forever begin

-   end
+   end // initial begin

 endinterface // IWishboneMaster
--- a/sim/if_wishbone_accessor.svh
+++ b/sim/if_wishbone_accessor.svh
@@ -66,8 +66,11 @@ virtual class CWishboneAccessor extends CBusAccessor;
        end

 //      $display("DS: %d", cycle.data.size());
-      
+
      put(cycle);
+      // wait for the transfer completion notification to avoid getting the result of the wrong transfer
+      // in case multiple threads are calling readm()/writem() in parallel.
+      @cycle.done;
      get(cycle);
      result  = cycle.result;
      
@@ -91,6 +94,9 @@ virtual class CWishboneAccessor extends CBusAccessor;
        end

      put(cycle);
+      // wait for the transfer completion notification to avoid getting the result of the wrong transfer
+      // in case multiple threads are calling readm()/writem() in parallel.
+      @cycle.done;
      get(cycle);

      for(i=0;i < addr.size(); i++)

--- a/sim/if_wishbone_types.svh
+++ b/sim/if_wishbone_types.svh
@@ -42,6 +42,7 @@ typedef struct  {
   wb_cycle_type_t ctype;
   wb_xfer_t data[$];
   wb_cycle_result_t result;
+   event done;
 } wb_cycle_t;

 typedef enum