diff --git a/src/main/scala/uncore/tilelink2/AsyncCrossing.scala b/src/main/scala/uncore/tilelink2/AsyncCrossing.scala
index 7736e7af..bd2788ea 100644
--- a/src/main/scala/uncore/tilelink2/AsyncCrossing.scala
+++ b/src/main/scala/uncore/tilelink2/AsyncCrossing.scala
@@ -138,7 +138,7 @@ class TLAsyncCrossing(depth: Int = 8, sync: Int = 3)(implicit p: Parameters) ext
 import unittest._
 
 class TLRAMAsyncCrossing(implicit p: Parameters) extends LazyModule {
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("AsyncCrossing"))
   val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff)))
   val fuzz = LazyModule(new TLFuzzer(5000))
   val cross = LazyModule(new TLAsyncCrossing)
diff --git a/src/main/scala/uncore/tilelink2/AtomicAutomata.scala b/src/main/scala/uncore/tilelink2/AtomicAutomata.scala
index 538b7565..ba9a444d 100644
--- a/src/main/scala/uncore/tilelink2/AtomicAutomata.scala
+++ b/src/main/scala/uncore/tilelink2/AtomicAutomata.scala
@@ -295,7 +295,7 @@ import unittest._
 
 class TLRAMAtomicAutomata()(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("AtomicAutomata"))
   val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff)))
 
   model.node := fuzz.node
diff --git a/src/main/scala/uncore/tilelink2/Atomics.scala b/src/main/scala/uncore/tilelink2/Atomics.scala
new file mode 100644
index 00000000..ccfc1a2d
--- /dev/null
+++ b/src/main/scala/uncore/tilelink2/Atomics.scala
@@ -0,0 +1,65 @@
+// See LICENSE.SiFive for license details.
+
+package uncore.tilelink2
+
+import Chisel._
+import config._
+import diplomacy._
+import uncore.tilelink2._
+import TLMessages._
+import TLPermissions._
+
+class Atomics(params: TLBundleParameters) extends Module
+{
+  val io = new Bundle {
+    val write    = Bool().flip // ignore opcode
+    val a        = new TLBundleA(params).flip
+    val data_in  = UInt(width = params.dataBits).flip
+    val data_out = UInt(width = params.dataBits)
+  }
+
+  // Arithmetic, what to do
+  val adder    = io.a.param(2)
+  val unsigned = io.a.param(1)
+  val take_max = io.a.param(0)
+
+  val signBit = io.a.mask & Cat(UInt(1), ~io.a.mask >> 1)
+  val inv_d = Mux(adder, io.data_in, ~io.data_in)
+  val sum = (FillInterleaved(8, io.a.mask) & io.a.data) + inv_d
+  def sign(x: UInt): Bool = (Cat(x.toBools.grouped(8).map(_.last).toList.reverse) & signBit).orR()
+  val sign_a = sign(io.a.data)
+  val sign_d = sign(io.data_in)
+  val sign_s = sign(sum)
+  val a_bigger_uneq = unsigned === sign_a // result if high bits are unequal
+  val a_bigger = Mux(sign_a === sign_d, !sign_s, a_bigger_uneq)
+  val pick_a = take_max === a_bigger
+
+  // Logical, what to do
+  val lut = Vec(Seq(
+    UInt(0x6),   // XOR
+    UInt(0xe),   // OR
+    UInt(0x8),   // AND
+    UInt(0xc)))( // SWAP
+    io.a.param(1,0))
+  val logical = Cat((io.a.data.toBools zip io.data_in.toBools).map { case (a, d) =>
+    lut(Cat(a, d))
+  }.reverse)
+
+  // Operation, what to do? (0=d, 1=a, 2=sum, 3=logical)
+  val select = Mux(io.write, UInt(1), Vec(Seq(
+    UInt(1),   // PutFullData
+    UInt(1),   // PutPartialData
+    Mux(adder, UInt(2), Mux(pick_a, UInt(1), UInt(0))), // ArithmeticData
+    UInt(3),   // LogicalData
+    UInt(0),   // Get
+    UInt(0),   // Hint
+    UInt(0),   // Acquire
+    UInt(0)))( // Overwrite
+    io.a.opcode))
+
+  // Only the masked bytes can be modified
+  val selects = io.a.mask.toBools.map(b => Mux(b, select, UInt(0)))
+  io.data_out := Cat(selects.zipWithIndex.map { case (s, i) =>
+    Vec(Seq(io.data_in, io.a.data, sum, logical).map(_((i + 1) * 8 - 1, i * 8)))(s)
+  }.reverse)
+}
diff --git a/src/main/scala/uncore/tilelink2/Fragmenter.scala b/src/main/scala/uncore/tilelink2/Fragmenter.scala
index fd06fe87..7676aa2e 100644
--- a/src/main/scala/uncore/tilelink2/Fragmenter.scala
+++ b/src/main/scala/uncore/tilelink2/Fragmenter.scala
@@ -264,7 +264,7 @@ import unittest._
 
 class TLRAMFragmenter(ramBeatBytes: Int, maxSize: Int)(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("Fragmenter"))
   val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff), beatBytes = ramBeatBytes))
 
   model.node := fuzz.node
diff --git a/src/main/scala/uncore/tilelink2/HintHandler.scala b/src/main/scala/uncore/tilelink2/HintHandler.scala
index 0775aa52..5e153e0c 100644
--- a/src/main/scala/uncore/tilelink2/HintHandler.scala
+++ b/src/main/scala/uncore/tilelink2/HintHandler.scala
@@ -112,7 +112,7 @@ import unittest._
 
 class TLRAMHintHandler()(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("HintHandler"))
   val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff)))
 
   model.node := fuzz.node
diff --git a/src/main/scala/uncore/tilelink2/RAMModel.scala b/src/main/scala/uncore/tilelink2/RAMModel.scala
index fb4e4dfd..2befed32 100644
--- a/src/main/scala/uncore/tilelink2/RAMModel.scala
+++ b/src/main/scala/uncore/tilelink2/RAMModel.scala
@@ -5,7 +5,7 @@ package uncore.tilelink2
 import Chisel._
 import config._
 import diplomacy._
-import util.GenericParameterizedBundle
+import util.{GenericParameterizedBundle, CRC}
 
 // We detect concurrent puts that put memory into an undefined state.
 // put0, put0Ack, put1, put1Ack => ok: defined
@@ -45,6 +45,7 @@ class TLRAMModel(log: String = "")(implicit p: Parameters) extends LazyModule
       val addressBits  = log2Up(endAddress)
       val countBits    = log2Up(endSourceId)
       val sizeBits     = edge.bundle.sizeBits
+      val divisor      = CRC.CRC_16F_4_2
 
       // Reset control logic
       val wipeIndex = RegInit(UInt(0, width = log2Ceil(endAddressHi) + 1))
@@ -156,13 +157,31 @@ class TLRAMModel(log: String = "")(implicit p: Parameters) extends LazyModule
       }
 
       val a_waddr = Mux(wipe, wipeIndex, a_addr_hi)
+      val a_shadow = shadow.map(_.read(a_waddr))
+      val a_known_old = !(Cat(a_shadow.map(!_.valid).reverse) & a_mask).orR
+      val alu = Module(new Atomics(a.params))
+      alu.io.write := Bool(false)
+      alu.io.a := a
+      alu.io.data_in := Cat(a_shadow.map(_.value).reverse)
+
+      val crc = Mem(endSourceId, UInt(width = 16))
+      val crc_valid = Mem(endSourceId, Bool())
+      val a_crc_acc = Mux(a_first, UInt(0), crc(a.source))
+      val a_crc_new = Cat(a_shadow.zipWithIndex.map { case (z, i) => Mux(a_mask(i), z.value, UInt(0)) }.reverse)
+      val a_crc = CRC(divisor, Cat(a_crc_acc, a_crc_new), 16 + beatBytes*8)
+      val a_crc_valid = a_known_old && Mux(a_first, Bool(true), crc_valid(a.source))
+      when (a_fire) {
+        crc.write(a.source, a_crc)
+        crc_valid.write(a.source, a_crc_valid)
+      }
+
       for (i <- 0 until beatBytes) {
         val data = Wire(new TLRAMModel.ByteMonitor(params))
         val busy = a_inc(i) =/= a_dec(i) + (!a_first).asUInt
         val amo = a.opcode === TLMessages.ArithmeticData || a.opcode === TLMessages.LogicalData
-        data.valid := Mux(wipe, Bool(false), (!busy || a_fifo) && !amo)
-        // !!! calculate the AMO?
-        data.value := a.data(8*(i+1)-1, 8*i)
+        val beat_amo = a.size <= UInt(log2Ceil(beatBytes))
+        data.valid := Mux(wipe, Bool(false), (!busy || a_fifo) && (!amo || (a_known_old && beat_amo)))
+        data.value := alu.io.data_out(8*(i+1)-1, 8*i)
         when (shadow_wen(i)) {
           shadow(i).write(a_waddr, data)
         }
@@ -206,7 +225,22 @@ class TLRAMModel(log: String = "")(implicit p: Parameters) extends LazyModule
       val d_shadow = shadow.map(_.read(d_addr_hi))
       val d_valid = valid(d.source)
 
+      // CRC check
+      val d_crc_reg = Reg(UInt(width = 16))
+      val d_crc_acc = Mux(d_first, UInt(0), d_crc_reg)
+      val d_crc_new = FillInterleaved(8, d_mask) & d.data
+      val d_crc = CRC(divisor, Cat(d_crc_acc, d_crc_new), 16 + beatBytes*8)
+      val crc_bypass = if (edge.manager.minLatency > 0) Bool(false) else a_fire && a.source === d.source
+      val d_crc_valid = Mux(crc_bypass, a_crc_valid, crc_valid.read(d.source))
+      val d_crc_check = Mux(crc_bypass, a_crc, crc.read(d.source))
+
+      val d_no_race_reg = Reg(Bool())
+      val d_no_race = Wire(init = d_no_race_reg)
+
       when (d_fire) {
+        d_crc_reg := d_crc
+        d_no_race_reg := d_no_race
+
         // Check the response is correct
         assert (d_size === d_flight.size)
         // addr_lo is allowed to differ
@@ -261,11 +295,24 @@ class TLRAMModel(log: String = "")(implicit p: Parameters) extends LazyModule
                 printf(", undefined (concurrent completed put)\n")
               } .otherwise {
                 printf("\n")
+                when (shadow.value =/= got) { printf("EXPECTED: 0x%x\n", shadow.value) }
                 assert (shadow.value === got)
               }
             }
           }
         }
+
+        when (d_flight.opcode === TLMessages.ArithmeticData || d_flight.opcode === TLMessages.LogicalData) {
+          val race = (d_inc zip d_dec) map { case (i, d) => i - d =/= UInt(1) }
+          when (d_first) { d_no_race := Bool(true) }
+          when ((Cat(race.reverse) & d_mask).orR) { d_no_race := Bool(false) }
+          when (d_last) {
+            val must_match = d_crc_valid && (d_fifo || (d_valid && d_no_race))
+            printf(log + " crc = 0x%x %d\n", d_crc, must_match.asUInt)
+            when (must_match && d_crc =/= d_crc_check) { printf("EXPECTED: 0x%x\n", d_crc_check) }
+            assert (!must_match || d_crc === d_crc_check)
+          }
+        }
       }
 
       val d_waddr = Mux(wipe, wipeIndex, d_addr_hi)
diff --git a/src/main/scala/uncore/tilelink2/RationalCrossing.scala b/src/main/scala/uncore/tilelink2/RationalCrossing.scala
index a736269c..e13bbbbf 100644
--- a/src/main/scala/uncore/tilelink2/RationalCrossing.scala
+++ b/src/main/scala/uncore/tilelink2/RationalCrossing.scala
@@ -149,10 +149,10 @@ class TLRationalCrossing(direction: RationalDirection = Symmetric)(implicit p: P
 /** Synthesizeable unit tests */
 import unittest._
 
-class TLRAMRationalCrossingSource(implicit p: Parameters) extends LazyModule {
+class TLRAMRationalCrossingSource(name: String)(implicit p: Parameters) extends LazyModule {
   val node = TLRationalOutputNode()
   val fuzz  = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel(name))
 
   model.node := fuzz.node
   node := TLRationalCrossingSource()(TLDelayer(0.25)(model.node))
@@ -180,19 +180,19 @@ class TLRAMRationalCrossingSink(direction: RationalDirection)(implicit p: Parame
 }
 
 class TLRAMRationalCrossing(implicit p: Parameters) extends LazyModule {
-  val sym_fast_source = LazyModule(new TLRAMRationalCrossingSource)
+  val sym_fast_source = LazyModule(new TLRAMRationalCrossingSource("RationalCrossing sym_fast"))
   val sym_slow_sink   = LazyModule(new TLRAMRationalCrossingSink(Symmetric))
   sym_slow_sink.node := sym_fast_source.node
 
-  val sym_slow_source = LazyModule(new TLRAMRationalCrossingSource)
+  val sym_slow_source = LazyModule(new TLRAMRationalCrossingSource("RationalCrossing sym_slow"))
   val sym_fast_sink   = LazyModule(new TLRAMRationalCrossingSink(Symmetric))
   sym_fast_sink.node := sym_slow_source.node
 
-  val fix_fast_source = LazyModule(new TLRAMRationalCrossingSource)
+  val fix_fast_source = LazyModule(new TLRAMRationalCrossingSource("RationalCrossing fast"))
   val fix_slow_sink   = LazyModule(new TLRAMRationalCrossingSink(FastToSlow))
   fix_slow_sink.node := fix_fast_source.node
 
-  val fix_slow_source = LazyModule(new TLRAMRationalCrossingSource)
+  val fix_slow_source = LazyModule(new TLRAMRationalCrossingSource("RationalCrossing slow"))
   val fix_fast_sink   = LazyModule(new TLRAMRationalCrossingSink(SlowToFast))
   fix_fast_sink.node := fix_slow_source.node
 
diff --git a/src/main/scala/uncore/tilelink2/SRAM.scala b/src/main/scala/uncore/tilelink2/SRAM.scala
index d287c094..2e9d9d35 100644
--- a/src/main/scala/uncore/tilelink2/SRAM.scala
+++ b/src/main/scala/uncore/tilelink2/SRAM.scala
@@ -91,7 +91,7 @@ import unittest._
 
 class TLRAMSimple(ramBeatBytes: Int)(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("SRAMSimple"))
   val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff), beatBytes = ramBeatBytes))
 
   model.node := fuzz.node
diff --git a/src/main/scala/uncore/tilelink2/TestRAM.scala b/src/main/scala/uncore/tilelink2/TestRAM.scala
index 74dd2f75..bab75674 100644
--- a/src/main/scala/uncore/tilelink2/TestRAM.scala
+++ b/src/main/scala/uncore/tilelink2/TestRAM.scala
@@ -67,7 +67,7 @@ import unittest._
 
 class TLRAMZeroDelay(ramBeatBytes: Int)(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("ZeroDelay"))
   val ram  = LazyModule(new TLTestRAM(AddressSet(0x0, 0x3ff), beatBytes = ramBeatBytes))
 
   model.node := fuzz.node
diff --git a/src/main/scala/uncore/tilelink2/WidthWidget.scala b/src/main/scala/uncore/tilelink2/WidthWidget.scala
index e066722a..36e154b3 100644
--- a/src/main/scala/uncore/tilelink2/WidthWidget.scala
+++ b/src/main/scala/uncore/tilelink2/WidthWidget.scala
@@ -176,7 +176,7 @@ import unittest._
 
 class TLRAMWidthWidget(first: Int, second: Int)(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("WidthWidget"))
   val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff)))
 
   model.node := fuzz.node
diff --git a/src/main/scala/uncore/tilelink2/Xbar.scala b/src/main/scala/uncore/tilelink2/Xbar.scala
index 7d122b3b..377198b9 100644
--- a/src/main/scala/uncore/tilelink2/Xbar.scala
+++ b/src/main/scala/uncore/tilelink2/Xbar.scala
@@ -215,7 +215,7 @@ import unittest._
 
 class TLRAMXbar(nManagers: Int)(implicit p: Parameters) extends LazyModule {
   val fuzz = LazyModule(new TLFuzzer(5000))
-  val model = LazyModule(new TLRAMModel)
+  val model = LazyModule(new TLRAMModel("Xbar"))
   val xbar = LazyModule(new TLXbar)
 
   model.node := fuzz.node
diff --git a/src/main/scala/unittest/Configs.scala b/src/main/scala/unittest/Configs.scala
index ac825820..4fdfad95 100644
--- a/src/main/scala/unittest/Configs.scala
+++ b/src/main/scala/unittest/Configs.scala
@@ -35,7 +35,8 @@ class WithTLSimpleUnitTests extends Config((site, here, up) => {
       Module(new uncore.tilelink2.TLRR0Test),
       Module(new uncore.tilelink2.TLRR1Test),
       Module(new uncore.tilelink2.TLRAMRationalCrossingTest),
-      Module(new uncore.tilelink2.TLRAMAsyncCrossingTest) ) }
+      Module(new uncore.tilelink2.TLRAMAsyncCrossingTest),
+      Module(new uncore.tilelink2.TLRAMAtomicAutomataTest) ) }
 })
 
 class WithTLWidthUnitTests extends Config((site, here, up) => {
diff --git a/src/main/scala/util/CRC.scala b/src/main/scala/util/CRC.scala
new file mode 100644
index 00000000..8dc2ab21
--- /dev/null
+++ b/src/main/scala/util/CRC.scala
@@ -0,0 +1,35 @@
+// See LICENSE.SiFive for license details.
+
+package util
+
+import Chisel._
+
+object CRC
+{
+  // A divisor of 0x1d5 is interpretted to be x^8 + x^7 + x^6 + x^4 + x^2 + 1
+  // Let n be the highest term in the divisor; n=8 in 0x1d5.
+  // Then, this function calculates c mod d, returning an n-bit UInt.
+  // coefficient.width must be <= width
+  def apply(divisor: BigInt, coefficient: UInt, width: Integer): UInt = {
+    require (divisor > 0 && divisor.testBit(0))
+    require (width > 0)
+    assert (coefficient >> width === UInt(0))
+    val n = log2Floor(divisor)
+    val m = width
+    if (m <= n) return coefficient
+
+    // Initialize the reduction matrix
+    val array = Array.tabulate(m) { BigInt(1) << _ }
+    // Reduce the matrix of terms larger than n
+    for {
+      i <- (n until m).reverse
+      j <- 0 to n
+      if divisor.testBit(j)
+    } array(i-(n-j)) ^= array(i)
+    // Construct the circuit
+    Cat(Seq.tabulate(n) { i => (UInt(array(i)) & coefficient).xorR } .reverse)
+  }
+
+  // Find more great CRC polynomials here: https://users.ece.cmu.edu/~koopman/crc/
+  val CRC_16F_4_2 = BigInt(0x1a2eb) // HD=4 for <32751 bits and HD=6 for <93 bits
+}