From 733fc8e65edc1d24d7d145f3de6db13b33c8eb81 Mon Sep 17 00:00:00 2001
From: Andrew Waterman <waterman@eecs.berkeley.edu>
Date: Tue, 20 Dec 2011 03:49:07 -0800
Subject: [PATCH] booth multiplier

---
 rocket/src/main/scala/dpath.scala      |  1 +
 rocket/src/main/scala/multiplier.scala | 77 ++++++++++++++++----------
 2 files changed, 49 insertions(+), 29 deletions(-)

diff --git a/rocket/src/main/scala/dpath.scala b/rocket/src/main/scala/dpath.scala
index 9feaaa16..a907faf6 100644
--- a/rocket/src/main/scala/dpath.scala
+++ b/rocket/src/main/scala/dpath.scala
@@ -292,6 +292,7 @@ class rocketDpath extends Component
  
   io.ctrl.mul_rdy        := mul.io.mul_rdy
   io.ctrl.mul_result_val := mul.io.result_val;
+  mul.io.result_rdy      := io.ctrl.mul_wb
   
   io.ctrl.ex_waddr := ex_reg_waddr; // for load/use hazard detection & bypass control
 
diff --git a/rocket/src/main/scala/multiplier.scala b/rocket/src/main/scala/multiplier.scala
index e1c17d8c..f3570bbf 100644
--- a/rocket/src/main/scala/multiplier.scala
+++ b/rocket/src/main/scala/multiplier.scala
@@ -10,63 +10,82 @@ class ioMultiplier(width: Int) extends Bundle {
   val mul_rdy = Bool('output);
   val dw      = UFix(1, 'input);
   val mul_fn  = UFix(2, 'input);
-  val mul_tag = UFix(5, 'input);
+  val mul_tag = UFix(CPU_TAG_BITS, 'input);
   val in0     = Bits(width, 'input);
   val in1     = Bits(width, 'input);
   
   // responses
   val result     = Bits(width, 'output);
-  val result_tag = UFix(5, 'output);
+  val result_tag = UFix(CPU_TAG_BITS, 'output);
   val result_val = Bool('output);
+  val result_rdy = Bool('input);
 }
 
 class rocketMultiplier extends Component {
   val io = new ioMultiplier(64);
+  val width = 64 + 2
+  val cycles = width/2
   
   val r_val = Reg(resetVal = Bool(false));
-  val r_dw  = Reg(resetVal = UFix(0,1));
-  val r_fn  = Reg(resetVal = UFix(0,3));
-  val r_tag = Reg(resetVal = UFix(0,5));
-  val r_lhs = Reg(resetVal = Bits(0,65));
-  val r_rhs = Reg(resetVal = Bits(0,65));
+  val r_dw  = Reg { UFix() }
+  val r_fn  = Reg { UFix() }
+  val r_tag = Reg { UFix() }
+  val r_lhs = Reg { Bits() }
+  val r_prod= Reg { Bits(width = width*2) }
+  val r_lsb = Reg { Bits() }
+  val r_cnt = Reg { UFix(width = log2up(cycles+1)) }
 
   val lhs_msb = Mux(io.dw === DW_64, io.in0(63), io.in0(31)).toBool
   val lhs_sign = ((io.mul_fn === MUL_HS) || (io.mul_fn === MUL_HSU)) && lhs_msb
   val lhs_hi = Mux(io.dw === DW_64, io.in0(63,32), Fill(32, lhs_sign))
-  val lhs = Cat(lhs_sign, lhs_hi, io.in0(31,0))
+  val lhs_in = Cat(lhs_sign, lhs_hi, io.in0(31,0))
 
   val rhs_msb = Mux(io.dw === DW_64, io.in1(63), io.in1(31)).toBool
   val rhs_sign = (io.mul_fn === MUL_HS) && rhs_msb
   val rhs_hi = Mux(io.dw === DW_64, io.in1(63,32), Fill(32, rhs_sign))
-  val rhs = Cat(rhs_sign, rhs_hi, io.in1(31,0))
+  val rhs_in = Cat(rhs_sign, rhs_sign, rhs_hi, io.in1(31,0))
   
-  r_val <== io.mul_val;
-  when (io.mul_val) {
+  when (io.mul_val && io.mul_rdy) {
+    r_val <== Bool(true)
+    r_cnt <== UFix(0, log2up(cycles+1))
     r_dw  <== io.dw
-    r_fn  <== io.mul_fn;
-    r_tag <== io.mul_tag;
-    r_lhs <== lhs;
-    r_rhs <== rhs;
+    r_fn  <== io.mul_fn
+    r_tag <== io.mul_tag
+    r_lhs <== lhs_in
+    r_prod<== rhs_in
+    r_lsb <== Bool(false)
+  }
+  when (io.result_val && io.result_rdy) {
+    r_val <== Bool(false)
   }
-  
-  val mul_result = r_lhs.toFix * r_rhs.toFix;
 
-  val mul_output64 = Mux(r_fn === MUL_LO, mul_result(63,0), mul_result(127,64))
-  val mul_output32 = Mux(r_fn === MUL_LO, mul_result(31,0), mul_result(63,31))
+  val lhs_sext = Cat(r_lhs(width-2), r_lhs(width-2), r_lhs).toUFix
+  val lhs_twice = Cat(r_lhs(width-2), r_lhs, Bits(0,1)).toUFix
+
+  val addend = Mux(r_prod(0) != r_lsb,     lhs_sext,
+               Mux(r_prod(0) != r_prod(1), lhs_twice,
+                                           UFix(0)));
+  val sub = r_prod(1)
+  val adder_lhs = Cat(r_prod(width*2-1), r_prod(width*2-1,width)).toUFix
+  val adder_rhs = Mux(sub, ~addend, addend)
+  val adder_out = (adder_lhs + adder_rhs + sub.toUFix)(width,0)
+
+  when (r_val && (r_cnt != UFix(cycles))) {
+    r_lsb  <== r_prod(1)
+    r_prod <== Cat(adder_out(width), adder_out, r_prod(width-1,2))
+    r_cnt <== r_cnt + UFix(1)
+  }
+
+  val mul_output64 = Mux(r_fn === MUL_LO, r_prod(63,0), r_prod(127,64))
+  val mul_output32 = Mux(r_fn === MUL_LO, r_prod(31,0), r_prod(63,31))
   val mul_output32_ext = Cat(Fill(32, mul_output32(31)), mul_output32)
   
   val mul_output = Mux(r_dw === DW_64, mul_output64, mul_output32_ext)
-  
-  // just a hack for now, this should be a parameterized number of stages
-  val r_result     = Reg(Reg(Reg(mul_output)));
-  val r_result_tag = Reg(Reg(Reg(r_tag))); 
-  val r_result_val = Reg(Reg(Reg(r_val)));
  
-  io.mul_rdy := Bool(true)
-  io.result := r_result;
-  io.result_tag := r_result_tag;
-  io.result_val := r_result_val;
-  
+  io.mul_rdy := !r_val
+  io.result := mul_output;
+  io.result_tag := r_tag;
+  io.result_val := r_val && (r_cnt === UFix(cycles))
 }
 
 }