replace verilog clock divider with one written in Chisel

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

@@ -4,6 +4,7 @@ package uncore.tilelink2
 import Chisel._
 import chisel3.util.LFSR16
 import unittest._
+import util.Pow2ClockDivider
 
 class IDMapGenerator(numIds: Int) extends Module {
   val w = log2Up(numIds)
@@ -208,15 +209,6 @@ 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)
@@ -240,17 +232,14 @@ class TLFuzzRAM extends LazyModule
     io.finished := fuzz.module.io.finished
 
     // Shove the RAM into another clock domain
-    val clocks = Module(new ClockDivider)
+    val clocks = Module(new Pow2ClockDivider(2))
     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
+    cross.module.io.out_reset := reset
   }
 }
 

src/main/scala/uncore/tilelink2/RegisterRouterTest.scala

@@ -3,6 +3,7 @@
 package uncore.tilelink2
 
 import Chisel._
+import util.Pow2ClockDivider
 
 object LFSR16Seed
 {
@@ -225,9 +226,7 @@ trait RRTest1Bundle
 
 trait RRTest1Module extends Module with HasRegMap
 {
-  val clocks = Module(new ClockDivider)
+  val clocks = Module(new Pow2ClockDivider(2))
-  clocks.io.clock_in := clock
-  clocks.io.reset_in := reset
 
   def x(bits: Int) = {
     val field = UInt(width = bits)
@@ -237,7 +236,7 @@ trait RRTest1Module extends Module with HasRegMap
     readCross.io.master_reset := reset
     readCross.io.master_allow := Bool(true)
     readCross.io.slave_clock := clocks.io.clock_out
-    readCross.io.slave_reset := clocks.io.reset_out
+    readCross.io.slave_reset := reset
     readCross.io.slave_allow := Bool(true)
 
     val writeCross = Module(new RegisterWriteCrossing(field))
@@ -245,7 +244,7 @@ trait RRTest1Module extends Module with HasRegMap
     writeCross.io.master_reset := reset
     writeCross.io.master_allow := Bool(true)
     writeCross.io.slave_clock := clocks.io.clock_out
-    writeCross.io.slave_reset := clocks.io.reset_out
+    writeCross.io.slave_reset := reset
     writeCross.io.slave_allow := Bool(true)
 
     readCross.io.slave_register := writeCross.io.slave_register

src/main/scala/util/ClockDivider.scala

@@ -0,0 +1,36 @@
+package util
+
+import Chisel._
+
+/** Divide the clock by 2 */
+class ClockDivider2 extends Module {
+  val io = new Bundle {
+    val clock_out = Clock(OUTPUT)
+  }
+
+  val clock_reg = Reg(Bool())
+  clock_reg := !clock_reg
+
+  io.clock_out := clock_reg.asClock
+}
+
+/** Divide the clock by power of 2 times.
+ *  @param pow2 divides the clock 2 ^ pow2 times
+ *  WARNING: This is meant for simulation use only. */
+class Pow2ClockDivider(pow2: Int) extends Module {
+  val io = new Bundle {
+    val clock_out = Clock(OUTPUT)
+  }
+
+  if (pow2 == 0) {
+    io.clock_out := clock
+  } else {
+    val dividers = Seq.fill(pow2) { Module(new ClockDivider2) }
+
+    dividers.init.zip(dividers.tail).map { case (last, next) =>
+      next.clock := last.io.clock_out
+    }
+
+    io.clock_out := dividers.last.io.clock_out
+  }
+}

vsim/Makefrag

@@ -9,7 +9,6 @@ bb_vsrcs = $(base_dir)/vsrc/DebugTransportModuleJtag.v \
 	$(base_dir)/vsrc/AsyncMailbox.v \
 	$(base_dir)/vsrc/AsyncResetReg.v \
 	$(base_dir)/vsrc/AsyncSetReg.v \
-	$(base_dir)/vsrc/ClockDivider.v \
 
 
 sim_vsrcs = \

vsrc/ClockDivider.v

@@ -1,19 +0,0 @@
-// 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