tilelink2: unit test for the clock crossing

src/main/scala/uncore/tilelink2/Fuzzer.scala

@@ -206,6 +206,15 @@ class TLFuzzer(
   }
 }
 
+class ClockDivider extends BlackBox {
+  val io = new Bundle {
+    val clock_in  = Clock(INPUT)
+    val reset_in  = Bool(INPUT)
+    val clock_out = Clock(OUTPUT)
+    val reset_out = Bool(OUTPUT)
+  }
+}
+
 class TLFuzzRAM extends LazyModule
 {
   val model = LazyModule(new TLRAMModel)
@@ -213,14 +222,29 @@ class TLFuzzRAM extends LazyModule
   val gpio = LazyModule(new RRTest1(0x400))
   val xbar = LazyModule(new TLXbar)
   val fuzz = LazyModule(new TLFuzzer(5000))
+  val cross = LazyModule(new TLAsyncCrossing)
 
   model.node := fuzz.node
   xbar.node := TLWidthWidget(TLHintHandler(model.node), 16)
-  ram.node := TLFragmenter(TLBuffer(xbar.node), 4, 256)
+  cross.node := TLFragmenter(TLBuffer(xbar.node), 4, 256)
+  ram.node := cross.node
   gpio.node := TLFragmenter(TLBuffer(xbar.node), 4, 32)
 
   lazy val module = new LazyModuleImp(this) with HasUnitTestIO {
     io.finished := fuzz.module.io.finished
+
+    // Shove the RAM into another clock domain
+    val clocks = Module(new ClockDivider)
+    ram.module.clock := clocks.io.clock_out
+    ram.module.reset := clocks.io.reset_out
+    clocks.io.clock_in := clock
+    clocks.io.reset_in := reset
+
+    // ... and safely cross TL2 into it
+    cross.module.io.in_clock := clock
+    cross.module.io.in_reset := reset
+    cross.module.io.out_clock := clocks.io.clock_out
+    cross.module.io.out_reset := clocks.io.reset_out
   }
 }
 

vsrc/ClockDivider.v

@@ -0,0 +1,19 @@
+// You can't divide clocks in Chisel
+module ClockDivider(
+  input  clock_in,
+  input  reset_in,
+  output clock_out,
+  output reset_out
+);
+
+  reg [2:0] shift = 3'b001;
+
+  always @(posedge clock_in)
+  begin
+    shift <= {shift[0], shift[2:1]};
+  end
+  
+  assign reset_out = reset_in;
+  assign clock_out = shift[0];
+
+endmodule