authors: Jason Lowe-Power
last edited: 2022-05-12 15:05:47 +0000

Configuring for a standard protocol

You can easily adapt the simple example configurations from this part to the other SLICC protocols in gem5. In this chapter, we will briefly look at an example with MI_example, though this can be easily extended to other protocols.

However, these simple configuration files will only work in syscall emulation mode. Full system mode adds some complications such as DMA controllers. These scripts can be extended to full system.

For MI_example, we can use exactly the same runscript as before (simple_ruby.py), we just need to implement a different MyCacheSystem (and import that file in simple_ruby.py). Below, is the classes needed for MI_example. There are only a couple of changes from MSI, mostly due to different naming schemes. You can download the file here.

class MyCacheSystem(RubySystem):

    def __init__(self):
        if buildEnv['PROTOCOL'] != 'MI_example':
            fatal("This system assumes MI_example!")

        super(MyCacheSystem, self).__init__()

    def setup(self, system, cpus, mem_ctrls):
        """Set up the Ruby cache subsystem. Note: This can't be done in the
           constructor because many of these items require a pointer to the
           ruby system (self). This causes infinite recursion in initialize()
           if we do this in the __init__.
        """
        # Ruby's global network.
        self.network = MyNetwork(self)

        # MI example uses 5 virtual networks
        self.number_of_virtual_networks = 5
        self.network.number_of_virtual_networks = 5

        # There is a single global list of all of the controllers to make it
        # easier to connect everything to the global network. This can be
        # customized depending on the topology/network requirements.
        # Create one controller for each L1 cache (and the cache mem obj.)
        # Create a single directory controller (Really the memory cntrl)
        self.controllers = \
            [L1Cache(system, self, cpu) for cpu in cpus] + \
            [DirController(self, system.mem_ranges, mem_ctrls)]

        # Create one sequencer per CPU. In many systems this is more
        # complicated since you have to create sequencers for DMA controllers
        # and other controllers, too.
        self.sequencers = [RubySequencer(version = i,
                                # I/D cache is combined and grab from ctrl
                                icache = self.controllers[i].cacheMemory,
                                dcache = self.controllers[i].cacheMemory,
                                clk_domain = self.controllers[i].clk_domain,
                                ) for i in range(len(cpus))]

        for i,c in enumerate(self.controllers[0:len(cpus)]):
            c.sequencer = self.sequencers[i]

        self.num_of_sequencers = len(self.sequencers)

        # Create the network and connect the controllers.
        # NOTE: This is quite different if using Garnet!
        self.network.connectControllers(self.controllers)
        self.network.setup_buffers()

        # Set up a proxy port for the system_port. Used for load binaries and
        # other functional-only things.
        self.sys_port_proxy = RubyPortProxy()
        system.system_port = self.sys_port_proxy.slave

        # Connect the cpu's cache, interrupt, and TLB ports to Ruby
        for i,cpu in enumerate(cpus):
            cpu.icache_port = self.sequencers[i].slave
            cpu.dcache_port = self.sequencers[i].slave
            isa = buildEnv['TARGET_ISA']
            if isa == 'x86':
                cpu.interrupts[0].pio = self.sequencers[i].master
                cpu.interrupts[0].int_master = self.sequencers[i].slave
                cpu.interrupts[0].int_slave = self.sequencers[i].master
            if isa == 'x86' or isa == 'arm':
                cpu.itb.walker.port = self.sequencers[i].slave
                cpu.dtb.walker.port = self.sequencers[i].slave

class L1Cache(L1Cache_Controller):

    _version = 0
    @classmethod
    def versionCount(cls):
        cls._version += 1 # Use count for this particular type
        return cls._version - 1

    def __init__(self, system, ruby_system, cpu):
        """CPUs are needed to grab the clock domain and system is needed for
           the cache block size.
        """
        super(L1Cache, self).__init__()

        self.version = self.versionCount()
        # This is the cache memory object that stores the cache data and tags
        self.cacheMemory = RubyCache(size = '16kB',
                               assoc = 8,
                               start_index_bit = self.getBlockSizeBits(system))
        self.clk_domain = cpu.clk_domain
        self.send_evictions = self.sendEvicts(cpu)
        self.ruby_system = ruby_system
        self.connectQueues(ruby_system)

    def getBlockSizeBits(self, system):
        bits = int(math.log(system.cache_line_size, 2))
        if 2**bits != system.cache_line_size.value:
            panic("Cache line size not a power of 2!")
        return bits

    def sendEvicts(self, cpu):
        """True if the CPU model or ISA requires sending evictions from caches
           to the CPU. Two scenarios warrant forwarding evictions to the CPU:
           1. The O3 model must keep the LSQ coherent with the caches
           2. The x86 mwait instruction is built on top of coherence
           3. The local exclusive monitor in ARM systems
        """
        if type(cpu) is DerivO3CPU or \
           buildEnv['TARGET_ISA'] in ('x86', 'arm'):
            return True
        return False

    def connectQueues(self, ruby_system):
        """Connect all of the queues for this controller.
        """
        self.mandatoryQueue = MessageBuffer()
        self.requestFromCache = MessageBuffer(ordered = True)
        self.requestFromCache.master = ruby_system.network.slave
        self.responseFromCache = MessageBuffer(ordered = True)
        self.responseFromCache.master = ruby_system.network.slave
        self.forwardToCache = MessageBuffer(ordered = True)
        self.forwardToCache.slave = ruby_system.network.master
        self.responseToCache = MessageBuffer(ordered = True)
        self.responseToCache.slave = ruby_system.network.master

class DirController(Directory_Controller):

    _version = 0
    @classmethod
    def versionCount(cls):
        cls._version += 1 # Use count for this particular type
        return cls._version - 1

    def __init__(self, ruby_system, ranges, mem_ctrls):
        """ranges are the memory ranges assigned to this controller.
        """
        if len(mem_ctrls) > 1:
            panic("This cache system can only be connected to one mem ctrl")
        super(DirController, self).__init__()
        self.version = self.versionCount()
        self.addr_ranges = ranges
        self.ruby_system = ruby_system
        self.directory = RubyDirectoryMemory()
        # Connect this directory to the memory side.
        self.memory = mem_ctrls[0].port
        self.connectQueues(ruby_system)

    def connectQueues(self, ruby_system):
        self.requestToDir = MessageBuffer(ordered = True)
        self.requestToDir.slave = ruby_system.network.master
        self.dmaRequestToDir = MessageBuffer(ordered = True)
        self.dmaRequestToDir.slave = ruby_system.network.master

        self.responseFromDir = MessageBuffer()
        self.responseFromDir.master = ruby_system.network.slave
        self.dmaResponseFromDir = MessageBuffer(ordered = True)
        self.dmaResponseFromDir.master = ruby_system.network.slave
        self.forwardFromDir = MessageBuffer()
        self.forwardFromDir.master = ruby_system.network.slave
        self.responseFromMemory = MessageBuffer()

class MyNetwork(SimpleNetwork):
    """A simple point-to-point network. This doesn't not use garnet.
    """

    def __init__(self, ruby_system):
        super(MyNetwork, self).__init__()
        self.netifs = []
        self.ruby_system = ruby_system

    def connectControllers(self, controllers):
        """Connect all of the controllers to routers and connect the routers
           together in a point-to-point network.
        """
        # Create one router/switch per controller in the system
        self.routers = [Switch(router_id = i) for i in range(len(controllers))]

        # Make a link from each controller to the router. The link goes
        # externally to the network.
        self.ext_links = [SimpleExtLink(link_id=i, ext_node=c,
                                        int_node=self.routers[i])
                          for i, c in enumerate(controllers)]

        # Make an "internal" link (internal to the network) between every pair
        # of routers.
        link_count = 0
        self.int_links = []
        for ri in self.routers:
            for rj in self.routers:
                if ri == rj: continue # Don't connect a router to itself!
                link_count += 1
                self.int_links.append(SimpleIntLink(link_id = link_count,
                                                    src_node = ri,
                                                    dst_node = rj))