diff --git a/src/main/scala/radiance/core/TensorDPU.scala b/src/main/scala/radiance/core/TensorDPU.scala
index 90dd2ec..9978a96 100644
--- a/src/main/scala/radiance/core/TensorDPU.scala
+++ b/src/main/scala/radiance/core/TensorDPU.scala
@@ -17,7 +17,7 @@ class DPUPipe extends Module with tile.HasFPUParameters {
     val in = Flipped(Valid(new Bundle {
       val a = Vec(dotProductDim, Bits((fLen).W))
       val b = Vec(dotProductDim, Bits((fLen).W))
-      val c = Vec(dotProductDim, Bits((fLen).W))
+      val c = Bits((fLen).W)
     }))
     val out = Valid(new Bundle {
       val data = Bits((fLen).W)
@@ -28,7 +28,7 @@ class DPUPipe extends Module with tile.HasFPUParameters {
 
   val in1 = io.in.bits.a.map(x => unbox(recode(x, S), S, Some(tile.FType.S)))
   val in2 = io.in.bits.b.map(x => unbox(recode(x, S), S, Some(tile.FType.S)))
-  val in3 = io.in.bits.c.map(x => unbox(recode(x, S), S, Some(tile.FType.S)))
+  val in3 = unbox(recode(io.in.bits.c, S), S, Some(tile.FType.S))
 
   // val fma = Module(new MulAddRecFNPipe(2, t.exp, t.sig))
   // fma.io.validin := io.in.valid
@@ -43,12 +43,14 @@ class DPUPipe extends Module with tile.HasFPUParameters {
   dpu.io.in.valid := io.in.valid
   dpu.io.in.bits.a := in1
   dpu.io.in.bits.b := in2
-  // FIXME: in3 unused
+  dpu.io.in.bits.c := in3
 
   io.out.valid := dpu.io.out.valid
   io.out.bits.data := ieee(box(dpu.io.out.bits.data, S))
 }
 
+// Computes d = a(0)*b(0) + ... + a(3)*b(3) + c.
+// Fully pipelined with a fixed latency of 4 cycles.
 class DotProductPipe(dim: Int, expWidth: Int, sigWidth: Int) extends Module {
   require(dim == 4, "DPU currently only supports dimension 4")
 
@@ -57,6 +59,7 @@ class DotProductPipe(dim: Int, expWidth: Int, sigWidth: Int) extends Module {
     val in = Flipped(Valid(new Bundle {
       val a = Vec(4, Bits((recFLen).W))
       val b = Vec(4, Bits((recFLen).W))
+      val c = Bits((recFLen).W)
       // val roundingMode   = UInt(3.W)
       // val detectTininess = UInt(1.W)
     }))
@@ -74,6 +77,7 @@ class DotProductPipe(dim: Int, expWidth: Int, sigWidth: Int) extends Module {
   }
 
   val mulStageOut = Pipe(io.in.valid, VecInit(mul.map(_.io.out)))
+  val mulStageC   = Pipe(io.in.valid, io.in.bits.c)
 
   // mul stage end -------------------------------------------------------
 
@@ -87,8 +91,9 @@ class DotProductPipe(dim: Int, expWidth: Int, sigWidth: Int) extends Module {
   }
 
   val add1StageOut = Pipe(mulStageOut.valid, VecInit(add1.map(_.io.out)))
+  val add1StageC   = Pipe(mulStageC)
 
-  // add stage 1 end -----------------------------------------------------
+  // add1 stage end -----------------------------------------------------
 
   val add2 = Module(new hardfloat.AddRecFN(expWidth, sigWidth))
   add2.io.subOp := 0.U // FIXME
@@ -98,11 +103,23 @@ class DotProductPipe(dim: Int, expWidth: Int, sigWidth: Int) extends Module {
   add2.io.roundingMode := hardfloat.consts.round_near_even
   add2.io.detectTininess := hardfloat.consts.tininess_afterRounding
 
-  io.out.valid := Pipe(add1StageOut.valid, false.B).valid
-  io.out.bits.data := Pipe(add1StageOut.valid, add2.io.out).bits
+  val add2StageOut = Pipe(add1StageOut.valid, add2.io.out)
+  val add2StageC   = Pipe(add1StageC)
+
+  // add2 stage end -----------------------------------------------------
+
+  val acc = Module(new hardfloat.AddRecFN(expWidth, sigWidth))
+  acc.io.subOp := 0.U // FIXME
+  acc.io.a := add2StageOut.bits
+  acc.io.b := add2StageC.bits
+  acc.io.roundingMode := hardfloat.consts.round_near_even
+  acc.io.detectTininess := hardfloat.consts.tininess_afterRounding
+
+  io.out.valid := Pipe(add2StageOut.valid, false.B).valid
+  io.out.bits.data := Pipe(add2StageOut.valid, acc.io.out).bits
   // FIXME: exception output ignored
 
-  // add stage 2 end -----------------------------------------------------
+  // acc stage end -----------------------------------------------------
 }
 
 class MulAddRecFNPipe(latency: Int, expWidth: Int, sigWidth: Int) extends Module {
diff --git a/src/test/scala/radiance/TensorDPUTest.scala b/src/test/scala/radiance/TensorDPUTest.scala
index 5993edf..55ef3a7 100644
--- a/src/test/scala/radiance/TensorDPUTest.scala
+++ b/src/test/scala/radiance/TensorDPUTest.scala
@@ -60,13 +60,20 @@ class DPUPipeTest extends AnyFlatSpec with ChiselScalatestTester {
         c.io.in.bits.b(1).poke(0x40000000L.U(64.W))
         c.io.in.bits.b(2).poke(0x40000000L.U(64.W))
         c.io.in.bits.b(3).poke(0x40000000L.U(64.W))
+        c.io.in.bits.c   .poke(0x40400000L.U(64.W))
+
         c.clock.step()
         c.io.in.valid.poke(false.B)
         c.clock.step()
         c.clock.step()
+        c.clock.step()
+        // 4-cycle latency
+
         c.io.out.valid.expect(true.B)
         c.io.out.bits.data.expect(0x40e00000L.U)
+
         c.clock.step()
+
         c.io.out.valid.expect(false.B)
       }
   }