From fda4c2bd7696d79444b094cae2af6c9267f43534 Mon Sep 17 00:00:00 2001
From: Megan Wachs <megan@sifive.com>
Date: Thu, 8 Sep 2016 20:01:03 -0700
Subject: [PATCH] Add a way to create Async Reset Registers and a way to easily
 access them with TL2

---
 .../scala/uncore/tilelink2/RegField.scala     | 11 +++
 src/main/scala/uncore/util/BlackBoxRegs.scala | 84 +++++++++++++++++++
 vsim/Makefrag                                 |  3 +-
 vsrc/AsyncResetReg.v                          | 51 +++++++++++
 4 files changed, 148 insertions(+), 1 deletion(-)
 create mode 100644 src/main/scala/uncore/util/BlackBoxRegs.scala
 create mode 100644 vsrc/AsyncResetReg.v

diff --git a/src/main/scala/uncore/tilelink2/RegField.scala b/src/main/scala/uncore/tilelink2/RegField.scala
index 32a65c0d..d4b34743 100644
--- a/src/main/scala/uncore/tilelink2/RegField.scala
+++ b/src/main/scala/uncore/tilelink2/RegField.scala
@@ -4,6 +4,8 @@ package uncore.tilelink2
 
 import Chisel._
 
+import uncore.util.{SimpleRegIO}
+
 case class RegReadFn private(combinational: Boolean, fn: (Bool, Bool) => (Bool, Bool, UInt))
 object RegReadFn
 {
@@ -81,6 +83,15 @@ object RegField
   // Setting takes priority over clearing.
   def w1ToClear(n: Int, reg: UInt, set: UInt): RegField =
     RegField(n, reg, RegWriteFn((valid, data) => { reg := ~(~reg | Mux(valid, data, UInt(0))) | set; Bool(true) }))
+
+  // This RegField wraps an explicit register
+  // (e.g. Black-Boxed Register) to create a R/W register.
+  def rwReg(n: Int, bb: SimpleRegIO) : RegField =
+    RegField(n, bb.q, RegWriteFn((valid, data) => {
+      bb.en := valid
+      bb.d := data
+      Bool(true)
+    }))
 }
 
 trait HasRegMap
diff --git a/src/main/scala/uncore/util/BlackBoxRegs.scala b/src/main/scala/uncore/util/BlackBoxRegs.scala
new file mode 100644
index 00000000..21fe09f0
--- /dev/null
+++ b/src/main/scala/uncore/util/BlackBoxRegs.scala
@@ -0,0 +1,84 @@
+package uncore.util
+
+import Chisel._
+
+import cde.{Parameters}
+import junctions.{ParameterizedBundle}
+
+/** This black-boxes an Async Reset
+  * Reg.
+  *  
+  * Because Chisel doesn't support
+  * parameterized black boxes, 
+  * we unfortunately have to 
+  * instantiate a number of these.
+  *  
+  *  Do not confuse an asynchronous
+  *  reset signal with an asynchronously
+  *  reset reg. You should still 
+  *  properly synchronize your reset 
+  *  deassertion.
+  *  
+  *  @param d Data input
+  *  @param q Data Output
+  *  @param clk Clock Input
+  *  @param rst Reset Input
+  *  
+  *  @param init Value to write at Reset. 
+  *  This is a constant, 
+  *  but this construction
+  *  will likely make backend flows
+  *  and lint tools unhappy.
+  * 
+  */
+
+class AsyncResetReg  extends BlackBox {
+
+  val io = new Bundle {
+    val d = Bool(INPUT)
+    val q = Bool(OUTPUT)
+
+    val clk = Clock(INPUT)
+    val rst = Bool(INPUT)
+
+    val init = Bool(INPUT)
+  }
+
+}
+
+
+class SimpleRegIO(val w: Int)(implicit val p: Parameters) extends ParameterizedBundle()(p){
+
+  val d = UInt(INPUT, width = w)
+  val q = UInt(OUTPUT, width = w)
+
+  val en = Bool(INPUT)
+
+}
+
+class AsyncResetRegVec(val w: Int, val init: Int)(implicit val p: Parameters) extends Module {
+
+  val io = new SimpleRegIO(w)(p)
+
+  val bb_q = Wire(UInt(width = w))
+  val bb_d = Wire(UInt(width = w))
+
+  val init_val = Wire(UInt(width = w))
+  init_val := UInt(init, width = w)
+
+  val async_regs = List.fill(w)(Module (new AsyncResetReg))
+
+  bb_q := (async_regs.map(_.io.q)).asUInt()
+  bb_d := Mux(io.en , io.d , bb_q)
+
+  io.q := bb_q
+
+  
+  for ((reg, idx) <- async_regs.zipWithIndex) {
+    reg.io.clk := clock
+    reg.io.rst := reset
+    reg.io.init := init_val(idx)
+    reg.io.d := bb_d(idx)
+  }
+
+}
diff --git a/vsim/Makefrag b/vsim/Makefrag
index a2f5559d..3abb2b4e 100644
--- a/vsim/Makefrag
+++ b/vsim/Makefrag
@@ -6,7 +6,8 @@
 
 bb_vsrcs = $(base_dir)/vsrc/DebugTransportModuleJtag.v \
 	$(base_dir)/vsrc/jtag_vpi.v \
-	$(base_dir)/vsrc/AsyncMailbox.v
+	$(base_dir)/vsrc/AsyncMailbox.v \
+	$(base_dir)/vsrc/AsyncResetReg.v
 
 sim_vsrcs = \
 	$(generated_dir)/$(MODEL).$(CONFIG).v \
diff --git a/vsrc/AsyncResetReg.v b/vsrc/AsyncResetReg.v
new file mode 100644
index 00000000..3adf16b1
--- /dev/null
+++ b/vsrc/AsyncResetReg.v
@@ -0,0 +1,51 @@
+
+
+/** This black-boxes an Async Reset
+  * Reg.
+  *  
+  * Because Chisel doesn't support
+  * parameterized black boxes, 
+  * we unfortunately have to 
+  * instantiate a number of these.
+  *  
+  *  Do not confuse an asynchronous
+  *  reset signal with an asynchronously
+  *  reset reg. You should still 
+  *  properly synchronize your reset 
+  *  deassertion.
+  *  
+  *  @param d Data input
+  *  @param q Data Output
+  *  @param clk Clock Input
+  *  @param rst Reset Input
+  *  
+  *  @param init Value to write at Reset. 
+  *  This is a constant, 
+  *  but this construction
+  *  will likely make backend flows
+  *  and lint tools unhappy.
+  * 
+  */
+
+module AsyncResetReg (
+                      input      d,
+                      output reg q,
+
+                      input      clk,
+                      input      rst,
+                      
+                      input      init);
+
+   always @(posedge clk or posedge rst) begin
+
+      if (rst) begin
+         q <= init;
+      end else begin
+         q <= d;
+      end
+   
+   end
+   
+
+endmodule // AsyncResetReg
+