learning_gem5: Adding code for SimpleCache

This is the rest of the code for part 2.

See http://learning.gem5.org/book/part2/simplecache.html

Change-Id: I5db099266a1196914656be3858fdd5fb4f8eab48
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5023
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>

5 files changed, 956 insertions, 0 deletions

diff --git a/configs/learning_gem5/part2/simple_cache.py b/configs/learning_gem5/part2/simple_cache.py
new file mode 100644
index 000000000..a07147caf
--- /dev/null
+++ b/configs/learning_gem5/part2/simple_cache.py
@@ -0,0 +1,101 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2017 Jason Lowe-Power
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+# Authors: Jason Lowe-Power
+
+""" This file creates a barebones system and executes 'hello', a simple Hello
+World application. Adds a simple cache between the CPU and the membus.
+
+This config file assumes that the x86 ISA was built.
+"""
+
+# import the m5 (gem5) library created when gem5 is built
+import m5
+# import all of the SimObjects
+from m5.objects import *
+
+# create the system we are going to simulate
+system = System()
+
+# Set the clock fequency of the system (and all of its children)
+system.clk_domain = SrcClockDomain()
+system.clk_domain.clock = '1GHz'
+system.clk_domain.voltage_domain = VoltageDomain()
+
+# Set up the system
+system.mem_mode = 'timing'               # Use timing accesses
+system.mem_ranges = [AddrRange('512MB')] # Create an address range
+
+# Create a simple CPU
+system.cpu = TimingSimpleCPU()
+
+# Create a memory bus, a coherent crossbar, in this case
+system.membus = SystemXBar()
+
+# Create a simple cache
+system.cache = SimpleCache(size='1kB')
+
+# Connect the I and D cache ports of the CPU to the memobj.
+# Since cpu_side is a vector port, each time one of these is connected, it will
+# create a new instance of the CPUSidePort class
+system.cpu.icache_port = system.cache.cpu_side
+system.cpu.dcache_port = system.cache.cpu_side
+
+# Hook the cache up to the memory bus
+system.cache.mem_side = system.membus.slave
+
+# create the interrupt controller for the CPU and connect to the membus
+system.cpu.createInterruptController()
+system.cpu.interrupts[0].pio = system.membus.master
+system.cpu.interrupts[0].int_master = system.membus.slave
+system.cpu.interrupts[0].int_slave = system.membus.master
+
+# Create a DDR3 memory controller and connect it to the membus
+system.mem_ctrl = DDR3_1600_8x8()
+system.mem_ctrl.range = system.mem_ranges[0]
+system.mem_ctrl.port = system.membus.master
+
+# Connect the system up to the membus
+system.system_port = system.membus.slave
+
+# Create a process for a simple "Hello World" application
+process = Process()
+# Set the command
+# cmd is a list which begins with the executable (like argv)
+process.cmd = ['tests/test-progs/hello/bin/x86/linux/hello']
+# Set the cpu to use the process as its workload and create thread contexts
+system.cpu.workload = process
+system.cpu.createThreads()
+
+# set up the root SimObject and start the simulation
+root = Root(full_system = False, system = system)
+# instantiate all of the objects we've created above
+m5.instantiate()
+
+print "Beginning simulation!"
+exit_event = m5.simulate()
+print 'Exiting @ tick %i because %s' % (m5.curTick(), exit_event.getCause())
diff --git a/src/learning_gem5/part2/SConscript b/src/learning_gem5/part2/SConscript
index f4605f39d..1a01d6de4 100644
--- a/src/learning_gem5/part2/SConscript
+++ b/src/learning_gem5/part2/SConscript
@@ -32,11 +32,14 @@ Import('*')
 SimObject('SimpleObject.py')
 SimObject('HelloObject.py')
 SimObject('SimpleMemobj.py')
+SimObject('SimpleCache.py')
 
 Source('simple_object.cc')
 Source('hello_object.cc')
 Source('goodbye_object.cc')
 Source('simple_memobj.cc')
+Source('simple_cache.cc')
 
 DebugFlag('HelloExample', "For Learning gem5 Part 2. Simple example debug flag")
 DebugFlag('SimpleMemobj', "For Learning gem5 Part 2.")
+DebugFlag('SimpleCache', "For Learning gem5 Part 2.")
diff --git a/src/learning_gem5/part2/SimpleCache.py b/src/learning_gem5/part2/SimpleCache.py
new file mode 100644
index 000000000..c0cdef9b8
--- /dev/null
+++ b/src/learning_gem5/part2/SimpleCache.py
@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2017 Jason Lowe-Power
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+# Authors: Jason Lowe-Power
+
+from m5.params import *
+from m5.proxy import *
+from MemObject import MemObject
+
+class SimpleCache(MemObject):
+    type = 'SimpleCache'
+    cxx_header = "learning_gem5/part2/simple_cache.hh"
+
+    # Vector port example. Both the instruction and data ports connect to this
+    # port which is automatically split out into two ports.
+    cpu_side = VectorSlavePort("CPU side port, receives requests")
+    mem_side = MasterPort("Memory side port, sends requests")
+
+    latency = Param.Cycles(1, "Cycles taken on a hit or to resolve a miss")
+
+    size = Param.MemorySize('16kB', "The size of the cache")
+
+    system = Param.System(Parent.any, "The system this cache is part of")
diff --git a/src/learning_gem5/part2/simple_cache.cc b/src/learning_gem5/part2/simple_cache.cc
new file mode 100644
index 000000000..4db2cfa52
--- /dev/null
+++ b/src/learning_gem5/part2/simple_cache.cc
@@ -0,0 +1,466 @@
+/*
+ * Copyright (c) 2017 Jason Lowe-Power
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Jason Lowe-Power
+ */
+
+#include "learning_gem5/part2/simple_cache.hh"
+
+#include "base/random.hh"
+#include "debug/SimpleCache.hh"
+#include "sim/system.hh"
+
+SimpleCache::SimpleCache(SimpleCacheParams *params) :
+    MemObject(params),
+    latency(params->latency),
+    blockSize(params->system->cacheLineSize()),
+    capacity(params->size / blockSize),
+    memPort(params->name + ".mem_side", this),
+    blocked(false), originalPacket(nullptr), waitingPortId(-1)
+{
+    // Since the CPU side ports are a vector of ports, create an instance of
+    // the CPUSidePort for each connection. This member of params is
+    // automatically created depending on the name of the vector port and
+    // holds the number of connections to this port name
+    for (int i = 0; i < params->port_cpu_side_connection_count; ++i) {
+        cpuPorts.emplace_back(name() + csprintf(".cpu_side[%d]", i), i, this);
+    }
+}
+
+BaseMasterPort&
+SimpleCache::getMasterPort(const std::string& if_name, PortID idx)
+{
+    panic_if(idx != InvalidPortID, "This object doesn't support vector ports");
+
+    // This is the name from the Python SimObject declaration in SimpleCache.py
+    if (if_name == "mem_side") {
+        return memPort;
+    } else {
+        // pass it along to our super class
+        return MemObject::getMasterPort(if_name, idx);
+    }
+}
+
+BaseSlavePort&
+SimpleCache::getSlavePort(const std::string& if_name, PortID idx)
+{
+    // This is the name from the Python SimObject declaration (SimpleMemobj.py)
+    if (if_name == "cpu_side" && idx < cpuPorts.size()) {
+        // We should have already created all of the ports in the constructor
+        return cpuPorts[idx];
+    } else {
+        // pass it along to our super class
+        return MemObject::getSlavePort(if_name, idx);
+    }
+}
+
+void
+SimpleCache::CPUSidePort::sendPacket(PacketPtr pkt)
+{
+    // Note: This flow control is very simple since the cache is blocking.
+
+    panic_if(blockedPacket != nullptr, "Should never try to send if blocked!");
+
+    // If we can't send the packet across the port, store it for later.
+    DPRINTF(SimpleCache, "Sending %s to CPU\n", pkt->print());
+    if (!sendTimingResp(pkt)) {
+        DPRINTF(SimpleCache, "failed!\n");
+        blockedPacket = pkt;
+    }
+}
+
+AddrRangeList
+SimpleCache::CPUSidePort::getAddrRanges() const
+{
+    return owner->getAddrRanges();
+}
+
+void
+SimpleCache::CPUSidePort::trySendRetry()
+{
+    if (needRetry && blockedPacket == nullptr) {
+        // Only send a retry if the port is now completely free
+        needRetry = false;
+        DPRINTF(SimpleCache, "Sending retry req.\n");
+        sendRetryReq();
+    }
+}
+
+void
+SimpleCache::CPUSidePort::recvFunctional(PacketPtr pkt)
+{
+    // Just forward to the cache.
+    return owner->handleFunctional(pkt);
+}
+
+bool
+SimpleCache::CPUSidePort::recvTimingReq(PacketPtr pkt)
+{
+    DPRINTF(SimpleCache, "Got request %s\n", pkt->print());
+
+    if (blockedPacket || needRetry) {
+        // The cache may not be able to send a reply if this is blocked
+        DPRINTF(SimpleCache, "Request blocked\n");
+        needRetry = true;
+        return false;
+    }
+    // Just forward to the cache.
+    if (!owner->handleRequest(pkt, id)) {
+        DPRINTF(SimpleCache, "Request failed\n");
+        // stalling
+        needRetry = true;
+        return false;
+    } else {
+        DPRINTF(SimpleCache, "Request succeeded\n");
+        return true;
+    }
+}
+
+void
+SimpleCache::CPUSidePort::recvRespRetry()
+{
+    // We should have a blocked packet if this function is called.
+    assert(blockedPacket != nullptr);
+
+    // Grab the blocked packet.
+    PacketPtr pkt = blockedPacket;
+    blockedPacket = nullptr;
+
+    DPRINTF(SimpleCache, "Retrying response pkt %s\n", pkt->print());
+    // Try to resend it. It's possible that it fails again.
+    sendPacket(pkt);
+
+    // We may now be able to accept new packets
+    trySendRetry();
+}
+
+void
+SimpleCache::MemSidePort::sendPacket(PacketPtr pkt)
+{
+    // Note: This flow control is very simple since the cache is blocking.
+
+    panic_if(blockedPacket != nullptr, "Should never try to send if blocked!");
+
+    // If we can't send the packet across the port, store it for later.
+    if (!sendTimingReq(pkt)) {
+        blockedPacket = pkt;
+    }
+}
+
+bool
+SimpleCache::MemSidePort::recvTimingResp(PacketPtr pkt)
+{
+    // Just forward to the cache.
+    return owner->handleResponse(pkt);
+}
+
+void
+SimpleCache::MemSidePort::recvReqRetry()
+{
+    // We should have a blocked packet if this function is called.
+    assert(blockedPacket != nullptr);
+
+    // Grab the blocked packet.
+    PacketPtr pkt = blockedPacket;
+    blockedPacket = nullptr;
+
+    // Try to resend it. It's possible that it fails again.
+    sendPacket(pkt);
+}
+
+void
+SimpleCache::MemSidePort::recvRangeChange()
+{
+    owner->sendRangeChange();
+}
+
+bool
+SimpleCache::handleRequest(PacketPtr pkt, int port_id)
+{
+    if (blocked) {
+        // There is currently an outstanding request so we can't respond. Stall
+        return false;
+    }
+
+    DPRINTF(SimpleCache, "Got request for addr %#x\n", pkt->getAddr());
+
+    // This cache is now blocked waiting for the response to this packet.
+    blocked = true;
+
+    // Store the port for when we get the response
+    assert(waitingPortId == -1);
+    waitingPortId = port_id;
+
+    // Schedule an event after cache access latency to actually access
+    schedule(new EventFunctionWrapper([this, pkt]{ accessTiming(pkt); },
+                                      name() + ".accessEvent", true),
+             clockEdge(latency));
+
+    return true;
+}
+
+bool
+SimpleCache::handleResponse(PacketPtr pkt)
+{
+    assert(blocked);
+    DPRINTF(SimpleCache, "Got response for addr %#x\n", pkt->getAddr());
+
+    // For now assume that inserts are off of the critical path and don't count
+    // for any added latency.
+    insert(pkt);
+
+    missLatency.sample(curTick() - missTime);
+
+    // If we had to upgrade the request packet to a full cache line, now we
+    // can use that packet to construct the response.
+    if (originalPacket != nullptr) {
+        DPRINTF(SimpleCache, "Copying data from new packet to old\n");
+        // We had to upgrade a previous packet. We can functionally deal with
+        // the cache access now. It better be a hit.
+        bool hit M5_VAR_USED = accessFunctional(originalPacket);
+        panic_if(!hit, "Should always hit after inserting");
+        originalPacket->makeResponse();
+        delete pkt; // We may need to delay this, I'm not sure.
+        pkt = originalPacket;
+        originalPacket = nullptr;
+    } // else, pkt contains the data it needs
+
+    sendResponse(pkt);
+
+    return true;
+}
+
+void SimpleCache::sendResponse(PacketPtr pkt)
+{
+    assert(blocked);
+    DPRINTF(SimpleCache, "Sending resp for addr %#x\n", pkt->getAddr());
+
+    int port = waitingPortId;
+
+    // The packet is now done. We're about to put it in the port, no need for
+    // this object to continue to stall.
+    // We need to free the resource before sending the packet in case the CPU
+    // tries to send another request immediately (e.g., in the same callchain).
+    blocked = false;
+    waitingPortId = -1;
+
+    // Simply forward to the memory port
+    cpuPorts[port].sendPacket(pkt);
+
+    // For each of the cpu ports, if it needs to send a retry, it should do it
+    // now since this memory object may be unblocked now.
+    for (auto& port : cpuPorts) {
+        port.trySendRetry();
+    }
+}
+
+void
+SimpleCache::handleFunctional(PacketPtr pkt)
+{
+    if (accessFunctional(pkt)) {
+        pkt->makeResponse();
+    } else {
+        memPort.sendFunctional(pkt);
+    }
+}
+
+void
+SimpleCache::accessTiming(PacketPtr pkt)
+{
+    bool hit = accessFunctional(pkt);
+
+    DPRINTF(SimpleCache, "%s for packet: %s\n", hit ? "Hit" : "Miss",
+            pkt->print());
+
+    if (hit) {
+        // Respond to the CPU side
+        hits++; // update stats
+        DDUMP(SimpleCache, pkt->getConstPtr<uint8_t>(), pkt->getSize());
+        pkt->makeResponse();
+        sendResponse(pkt);
+    } else {
+        misses++; // update stats
+        missTime = curTick();
+        // Forward to the memory side.
+        // We can't directly forward the packet unless it is exactly the size
+        // of the cache line, and aligned. Check for that here.
+        Addr addr = pkt->getAddr();
+        Addr block_addr = pkt->getBlockAddr(blockSize);
+        unsigned size = pkt->getSize();
+        if (addr == block_addr && size == blockSize) {
+            // Aligned and block size. We can just forward.
+            DPRINTF(SimpleCache, "forwarding packet\n");
+            memPort.sendPacket(pkt);
+        } else {
+            DPRINTF(SimpleCache, "Upgrading packet to block size\n");
+            panic_if(addr - block_addr + size > blockSize,
+                     "Cannot handle accesses that span multiple cache lines");
+            // Unaligned access to one cache block
+            assert(pkt->needsResponse());
+            MemCmd cmd;
+            if (pkt->isWrite() || pkt->isRead()) {
+                // Read the data from memory to write into the block.
+                // We'll write the data in the cache (i.e., a writeback cache)
+                cmd = MemCmd::ReadReq;
+            } else {
+                panic("Unknown packet type in upgrade size");
+            }
+
+            // Create a new packet that is blockSize
+            PacketPtr new_pkt = new Packet(pkt->req, cmd, blockSize);
+            new_pkt->allocate();
+
+            // Should now be block aligned
+            assert(new_pkt->getAddr() == new_pkt->getBlockAddr(blockSize));
+
+            // Save the old packet
+            originalPacket = pkt;
+
+            DPRINTF(SimpleCache, "forwarding packet\n");
+            memPort.sendPacket(new_pkt);
+        }
+    }
+}
+
+bool
+SimpleCache::accessFunctional(PacketPtr pkt)
+{
+    Addr block_addr = pkt->getBlockAddr(blockSize);
+    auto it = cacheStore.find(block_addr);
+    if (it != cacheStore.end()) {
+        if (pkt->isWrite()) {
+            // Write the data into the block in the cache
+            pkt->writeDataToBlock(it->second, blockSize);
+        } else if (pkt->isRead()) {
+            // Read the data out of the cache block into the packet
+            pkt->setDataFromBlock(it->second, blockSize);
+        } else {
+            panic("Unknown packet type!");
+        }
+        return true;
+    }
+    return false;
+}
+
+void
+SimpleCache::insert(PacketPtr pkt)
+{
+    // The packet should be aligned.
+    assert(pkt->getAddr() ==  pkt->getBlockAddr(blockSize));
+    // The address should not be in the cache
+    assert(cacheStore.find(pkt->getAddr()) == cacheStore.end());
+    // The pkt should be a response
+    assert(pkt->isResponse());
+
+    if (cacheStore.size() >= capacity) {
+        // Select random thing to evict. This is a little convoluted since we
+        // are using a std::unordered_map. See http://bit.ly/2hrnLP2
+        int bucket, bucket_size;
+        do {
+            bucket = random_mt.random(0, (int)cacheStore.bucket_count() - 1);
+        } while ( (bucket_size = cacheStore.bucket_size(bucket)) == 0 );
+        auto block = std::next(cacheStore.begin(bucket),
+                               random_mt.random(0, bucket_size - 1));
+
+        DPRINTF(SimpleCache, "Removing addr %#x\n", block->first);
+
+        // Write back the data.
+        // Create a new request-packet pair
+        RequestPtr req = new Request(block->first, blockSize, 0, 0);
+        PacketPtr new_pkt = new Packet(req, MemCmd::WritebackDirty, blockSize);
+        new_pkt->dataDynamic(block->second); // This will be deleted later
+
+        DPRINTF(SimpleCache, "Writing packet back %s\n", pkt->print());
+        // Send the write to memory
+        memPort.sendPacket(new_pkt);
+
+        // Delete this entry
+        cacheStore.erase(block->first);
+    }
+
+    DPRINTF(SimpleCache, "Inserting %s\n", pkt->print());
+    DDUMP(SimpleCache, pkt->getConstPtr<uint8_t>(), blockSize);
+
+    // Allocate space for the cache block data
+    uint8_t *data = new uint8_t[blockSize];
+
+    // Insert the data and address into the cache store
+    cacheStore[pkt->getAddr()] = data;
+
+    // Write the data into the cache
+    pkt->writeDataToBlock(data, blockSize);
+}
+
+AddrRangeList
+SimpleCache::getAddrRanges() const
+{
+    DPRINTF(SimpleCache, "Sending new ranges\n");
+    // Just use the same ranges as whatever is on the memory side.
+    return memPort.getAddrRanges();
+}
+
+void
+SimpleCache::sendRangeChange() const
+{
+    for (auto& port : cpuPorts) {
+        port.sendRangeChange();
+    }
+}
+
+void
+SimpleCache::regStats()
+{
+    // If you don't do this you get errors about uninitialized stats.
+    MemObject::regStats();
+
+    hits.name(name() + ".hits")
+        .desc("Number of hits")
+        ;
+
+    misses.name(name() + ".misses")
+        .desc("Number of misses")
+        ;
+
+    missLatency.name(name() + ".missLatency")
+        .desc("Ticks for misses to the cache")
+        .init(16) // number of buckets
+        ;
+
+    hitRatio.name(name() + ".hitRatio")
+        .desc("The ratio of hits to the total accesses to the cache")
+        ;
+
+    hitRatio = hits / (hits + misses);
+
+}
+
+
+SimpleCache*
+SimpleCacheParams::create()
+{
+    return new SimpleCache(this);
+}
diff --git a/src/learning_gem5/part2/simple_cache.hh b/src/learning_gem5/part2/simple_cache.hh
new file mode 100644
index 000000000..7d53ffed0
--- /dev/null
+++ b/src/learning_gem5/part2/simple_cache.hh
@@ -0,0 +1,339 @@
+/*
+ * Copyright (c) 2017 Jason Lowe-Power
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Jason Lowe-Power
+ */
+
+#ifndef __LEARNING_GEM5_SIMPLE_CACHE_SIMPLE_CACHE_HH__
+#define __LEARNING_GEM5_SIMPLE_CACHE_SIMPLE_CACHE_HH__
+
+#include <unordered_map>
+
+#include "mem/mem_object.hh"
+#include "params/SimpleCache.hh"
+
+/**
+ * A very simple cache object. Has a fully-associative data store with random
+ * replacement.
+ * This cache is fully blocking (not non-blocking). Only a single request can
+ * be outstanding at a time.
+ * This cache is a writeback cache.
+ */
+class SimpleCache : public MemObject
+{
+  private:
+
+    /**
+     * Port on the CPU-side that receives requests.
+     * Mostly just forwards requests to the cache (owner)
+     */
+    class CPUSidePort : public SlavePort
+    {
+      private:
+        /// Since this is a vector port, need to know what number this one is
+        int id;
+
+        /// The object that owns this object (SimpleCache)
+        SimpleCache *owner;
+
+        /// True if the port needs to send a retry req.
+        bool needRetry;
+
+        /// If we tried to send a packet and it was blocked, store it here
+        PacketPtr blockedPacket;
+
+      public:
+        /**
+         * Constructor. Just calls the superclass constructor.
+         */
+        CPUSidePort(const std::string& name, int id, SimpleCache *owner) :
+            SlavePort(name, owner), id(id), owner(owner), needRetry(false),
+            blockedPacket(nullptr)
+        { }
+
+        /**
+         * Send a packet across this port. This is called by the owner and
+         * all of the flow control is hanled in this function.
+         * This is a convenience function for the SimpleCache to send pkts.
+         *
+         * @param packet to send.
+         */
+        void sendPacket(PacketPtr pkt);
+
+        /**
+         * Get a list of the non-overlapping address ranges the owner is
+         * responsible for. All slave ports must override this function
+         * and return a populated list with at least one item.
+         *
+         * @return a list of ranges responded to
+         */
+        AddrRangeList getAddrRanges() const override;
+
+        /**
+         * Send a retry to the peer port only if it is needed. This is called
+         * from the SimpleCache whenever it is unblocked.
+         */
+        void trySendRetry();
+
+      protected:
+        /**
+         * Receive an atomic request packet from the master port.
+         * No need to implement in this simple cache.
+         */
+        Tick recvAtomic(PacketPtr pkt) override
+        { panic("recvAtomic unimpl."); }
+
+        /**
+         * Receive a functional request packet from the master port.
+         * Performs a "debug" access updating/reading the data in place.
+         *
+         * @param packet the requestor sent.
+         */
+        void recvFunctional(PacketPtr pkt) override;
+
+        /**
+         * Receive a timing request from the master port.
+         *
+         * @param the packet that the requestor sent
+         * @return whether this object can consume to packet. If false, we
+         *         will call sendRetry() when we can try to receive this
+         *         request again.
+         */
+        bool recvTimingReq(PacketPtr pkt) override;
+
+        /**
+         * Called by the master port if sendTimingResp was called on this
+         * slave port (causing recvTimingResp to be called on the master
+         * port) and was unsuccesful.
+         */
+        void recvRespRetry() override;
+    };
+
+    /**
+     * Port on the memory-side that receives responses.
+     * Mostly just forwards requests to the cache (owner)
+     */
+    class MemSidePort : public MasterPort
+    {
+      private:
+        /// The object that owns this object (SimpleCache)
+        SimpleCache *owner;
+
+        /// If we tried to send a packet and it was blocked, store it here
+        PacketPtr blockedPacket;
+
+      public:
+        /**
+         * Constructor. Just calls the superclass constructor.
+         */
+        MemSidePort(const std::string& name, SimpleCache *owner) :
+            MasterPort(name, owner), owner(owner), blockedPacket(nullptr)
+        { }
+
+        /**
+         * Send a packet across this port. This is called by the owner and
+         * all of the flow control is hanled in this function.
+         * This is a convenience function for the SimpleCache to send pkts.
+         *
+         * @param packet to send.
+         */
+        void sendPacket(PacketPtr pkt);
+
+      protected:
+        /**
+         * Receive a timing response from the slave port.
+         */
+        bool recvTimingResp(PacketPtr pkt) override;
+
+        /**
+         * Called by the slave port if sendTimingReq was called on this
+         * master port (causing recvTimingReq to be called on the slave
+         * port) and was unsuccesful.
+         */
+        void recvReqRetry() override;
+
+        /**
+         * Called to receive an address range change from the peer slave
+         * port. The default implementation ignores the change and does
+         * nothing. Override this function in a derived class if the owner
+         * needs to be aware of the address ranges, e.g. in an
+         * interconnect component like a bus.
+         */
+        void recvRangeChange() override;
+    };
+
+    /**
+     * Handle the request from the CPU side. Called from the CPU port
+     * on a timing request.
+     *
+     * @param requesting packet
+     * @param id of the port to send the response
+     * @return true if we can handle the request this cycle, false if the
+     *         requestor needs to retry later
+     */
+    bool handleRequest(PacketPtr pkt, int port_id);
+
+    /**
+     * Handle the respone from the memory side. Called from the memory port
+     * on a timing response.
+     *
+     * @param responding packet
+     * @return true if we can handle the response this cycle, false if the
+     *         responder needs to retry later
+     */
+    bool handleResponse(PacketPtr pkt);
+
+    /**
+     * Send the packet to the CPU side.
+     * This function assumes the pkt is already a response packet and forwards
+     * it to the correct port. This function also unblocks this object and
+     * cleans up the whole request.
+     *
+     * @param the packet to send to the cpu side
+     */
+    void sendResponse(PacketPtr pkt);
+
+    /**
+     * Handle a packet functionally. Update the data on a write and get the
+     * data on a read. Called from CPU port on a recv functional.
+     *
+     * @param packet to functionally handle
+     */
+    void handleFunctional(PacketPtr pkt);
+
+    /**
+     * Access the cache for a timing access. This is called after the cache
+     * access latency has already elapsed.
+     */
+    void accessTiming(PacketPtr pkt);
+
+    /**
+     * This is where we actually update / read from the cache. This function
+     * is executed on both timing and functional accesses.
+     *
+     * @return true if a hit, false otherwise
+     */
+    bool accessFunctional(PacketPtr pkt);
+
+    /**
+     * Insert a block into the cache. If there is no room left in the cache,
+     * then this function evicts a random entry t make room for the new block.
+     *
+     * @param packet with the data (and address) to insert into the cache
+     */
+    void insert(PacketPtr pkt);
+
+    /**
+     * Return the address ranges this cache is responsible for. Just use the
+     * same as the next upper level of the hierarchy.
+     *
+     * @return the address ranges this cache is responsible for
+     */
+    AddrRangeList getAddrRanges() const;
+
+    /**
+     * Tell the CPU side to ask for our memory ranges.
+     */
+    void sendRangeChange() const;
+
+    /// Latency to check the cache. Number of cycles for both hit and miss
+    const Cycles latency;
+
+    /// The block size for the cache
+    const unsigned blockSize;
+
+    /// Number of blocks in the cache (size of cache / block size)
+    const unsigned capacity;
+
+    /// Instantiation of the CPU-side port
+    std::vector<CPUSidePort> cpuPorts;
+
+    /// Instantiation of the memory-side port
+    MemSidePort memPort;
+
+    /// True if this cache is currently blocked waiting for a response.
+    bool blocked;
+
+    /// Packet that we are currently handling. Used for upgrading to larger
+    /// cache line sizes
+    PacketPtr originalPacket;
+
+    /// The port to send the response when we recieve it back
+    int waitingPortId;
+
+    /// For tracking the miss latency
+    Tick missTime;
+
+    /// An incredibly simple cache storage. Maps block addresses to data
+    std::unordered_map<Addr, uint8_t*> cacheStore;
+
+    /// Cache statistics
+    Stats::Scalar hits;
+    Stats::Scalar misses;
+    Stats::Histogram missLatency;
+    Stats::Formula hitRatio;
+
+  public:
+
+    /** constructor
+     */
+    SimpleCache(SimpleCacheParams *params);
+
+    /**
+     * Get a master port with a given name and index. This is used at
+     * binding time and returns a reference to a protocol-agnostic
+     * base master port.
+     *
+     * @param if_name Port name
+     * @param idx Index in the case of a VectorPort
+     *
+     * @return A reference to the given port
+     */
+    virtual BaseMasterPort& getMasterPort(const std::string& if_name,
+                                          PortID idx = InvalidPortID) override;
+
+    /**
+     * Get a slave port with a given name and index. This is used at
+     * binding time and returns a reference to a protocol-agnostic
+     * base master port.
+     *
+     * @param if_name Port name
+     * @param idx Index in the case of a VectorPort
+     *
+     * @return A reference to the given port
+     */
+    virtual BaseSlavePort& getSlavePort(const std::string& if_name,
+                                        PortID idx = InvalidPortID) override;
+
+    /**
+     * Register the stats
+     */
+    void regStats() override;
+};
+
+
+#endif // __LEARNING_GEM5_SIMPLE_CACHE_SIMPLE_CACHE_HH__