mock-array: pipeline lsb does max four CEs before registering

Signed-off-by: Øyvind Harboe <[email protected]>

Author: oharboe

flow/designs/src/mock-array/Element.v

@@ -28,14 +28,15 @@ module Element(
   reg [63:0] REG_1;
   reg [63:0] REG_2;
   reg [63:0] REG_3;
+  reg  REG_4;
   assign io_outs_down = REG_3;
   assign io_outs_right = REG_2;
   assign io_outs_up = REG_1;
   assign io_outs_left = REG;
   assign io_lsbOuts_0 = io_lsbIns_1;
   assign io_lsbOuts_1 = io_lsbIns_2;
   assign io_lsbOuts_2 = io_lsbIns_3;
-  assign io_lsbOuts_3 = io_lsbIns_4;
+  assign io_lsbOuts_3 = REG_4;
   assign io_lsbOuts_4 = io_lsbIns_5;
   assign io_lsbOuts_5 = io_lsbIns_6;
   assign io_lsbOuts_6 = io_lsbIns_7;
@@ -45,5 +46,6 @@ module Element(
     REG_1 <= io_ins_right;
     REG_2 <= io_ins_up;
     REG_3 <= io_ins_left;
+    REG_4 <= io_lsbIns_4;
   end
 endmodule

flow/designs/src/mock-array/src/test/scala/MockArray.scala

@@ -70,8 +70,22 @@ class MockArray(width: Int, height: Int, singleElementWidth: Int)
       case (a, b) => a := b
     }
 
-    // Combinational logic
-    io.lsbOuts := io.lsbIns.drop(1) ++ Seq(io.outs.asSeq.head(0)(0))
+    // Combinational logic, but a maximum flight path of 4 elements
+    val MAX_FLIGHT = 4
+    io.lsbOuts := (io.lsbIns
+      .drop(1)
+      .reverse
+      .sliding(MAX_FLIGHT, MAX_FLIGHT)
+      .map { lsbs =>
+        if (lsbs.length < MAX_FLIGHT) {
+          lsbs
+        } else {
+          lsbs.dropRight(1) ++ Seq(RegNext(lsbs.last))
+        }
+      })
+      .flatten
+      .toSeq
+      .reverse ++ Seq(io.outs.asSeq.head(0)(0))
   }
 
   val ces = Seq.fill(height)(Seq.fill(width)(Module(new Element())))