[hardware] 🐛 Filter operand queue ready from sldu and addrgen

The addrgen-sldu operand queue is common to slide unit and addrgen. Since it's shared, we should be sure not to sample a spurious ready from the wrong unit, i.e., when we are feeding the addrgen, we don't want spurious readies from the slide unit. The units should be responsible for avoiding sampling wrong data, but spurious ready signals can happen in specific corner cases. Fixing this without impacting timing is hard, so we just mask the ready signals here as well to avoid bugs.
pulp-platform · Nov 28, 2023 · 05fda3a · 05fda3a
1 parent 130d14c
commit 05fda3a
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Showing 2 changed files with 33 additions and 16 deletions.
diff --git a/hardware/src/lane/operand_queues_stage.sv b/hardware/src/lane/operand_queues_stage.sv
@@ -208,25 +208,41 @@ module operand_queues_stage import ara_pkg::*; import rvv_pkg::*; import cf_math
    *  Slide Unit  *
    ****************/
 
+  // This operand queue is common to slide unit and addrgen.
+  // Since it's shared, we should be sure not to sample a
+  // spurious ready from the wrong unit, i.e., when we are
+  // feeding the addrgen, we don't want spurious readies from
+  // the slide unit. The units should be responsible for avoiding
+  // sampling wrong data, but spurious ready signals can happen in
+  // specific corner cases. Fixing this without impacting timing is
+  // hard, so we just mask the ready signals here as well to avoid
+  // bugs.
+  logic sldu_operand_ready_filtered;
+  logic addrgen_operand_ready_filtered;
+  assign sldu_operand_ready_filtered = sldu_operand_ready_i &
+    (sldu_addrgen_operand_target_fu_o == ALU_SLDU);
+  assign addrgen_operand_ready_filtered = addrgen_operand_ready_i &
+    (sldu_addrgen_operand_target_fu_o == MFPU_ADDRGEN);
+
   operand_queue #(
     .CmdBufDepth   (VlduInsnQueueDepth),
     .DataBufDepth  (2                 ),
     .FPUSupport    (FPUSupport        ),
     .NrLanes       (NrLanes           )
   ) i_operand_queue_slide_addrgen_a (
-    .clk_i                    (clk_i                                         ),
-    .rst_ni                   (rst_ni                                        ),
-    .lane_id_i                (lane_id_i                                     ),
-    .operand_queue_cmd_i      (operand_queue_cmd_i[SlideAddrGenA]            ),
-    .operand_queue_cmd_valid_i(operand_queue_cmd_valid_i[SlideAddrGenA]      ),
-    .operand_i                (operand_i[SlideAddrGenA]                      ),
-    .operand_valid_i          (operand_valid_i[SlideAddrGenA]                ),
-    .operand_issued_i         (operand_issued_i[SlideAddrGenA]               ),
-    .operand_queue_ready_o    (operand_queue_ready_o[SlideAddrGenA]          ),
-    .operand_o                (sldu_addrgen_operand_o                        ),
-    .operand_target_fu_o      (sldu_addrgen_operand_target_fu_o              ),
-    .operand_valid_o          (sldu_addrgen_operand_valid_o                  ),
-    .operand_ready_i          (addrgen_operand_ready_i | sldu_operand_ready_i)
+    .clk_i                    (clk_i                                                       ),
+    .rst_ni                   (rst_ni                                                      ),
+    .lane_id_i                (lane_id_i                                                   ),
+    .operand_queue_cmd_i      (operand_queue_cmd_i[SlideAddrGenA]                          ),
+    .operand_queue_cmd_valid_i(operand_queue_cmd_valid_i[SlideAddrGenA]                    ),
+    .operand_i                (operand_i[SlideAddrGenA]                                    ),
+    .operand_valid_i          (operand_valid_i[SlideAddrGenA]                              ),
+    .operand_issued_i         (operand_issued_i[SlideAddrGenA]                             ),
+    .operand_queue_ready_o    (operand_queue_ready_o[SlideAddrGenA]                        ),
+    .operand_o                (sldu_addrgen_operand_o                                      ),
+    .operand_target_fu_o      (sldu_addrgen_operand_target_fu_o                            ),
+    .operand_valid_o          (sldu_addrgen_operand_valid_o                                ),
+    .operand_ready_i          (addrgen_operand_ready_filtered | sldu_operand_ready_filtered)
   );
 
   /////////////////

diff --git a/hardware/src/vlsu/addrgen.sv b/hardware/src/vlsu/addrgen.sv
@@ -324,9 +324,10 @@ module addrgen import ara_pkg::*; import rvv_pkg::*; #(
               // Bump lane pointer
               elm_ptr_d       = '0;
               word_lane_ptr_d += 1;
-              if (word_lane_ptr_q == NrLanes - 1)
-              // Ready for the next full word
-              addrgen_operand_ready_o = 1'b1;
+              if (word_lane_ptr_q == NrLanes - 1) begin
+                // Ready for the next full word
+                addrgen_operand_ready_o = 1'b1;
+              end
             end else begin
               // Bump element pointer
               elm_ptr_d += 1;