XBar.py revision 10719:b4fc9ad648aa 
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39# Authors: Nathan Binkert
40#          Andreas Hansson
41
42from MemObject import MemObject
43from System import System
44from m5.params import *
45from m5.proxy import *
46from m5.SimObject import SimObject
47
48class BaseXBar(MemObject):
49    type = 'BaseXBar'
50    abstract = True
51    cxx_header = "mem/xbar.hh"
52
53    slave = VectorSlavePort("Vector port for connecting masters")
54    master = VectorMasterPort("Vector port for connecting slaves")
55
56    # Latencies governing the time taken for the variuos paths a
57    # packet has through the crossbar. Note that the crossbar itself
58    # does not add the latency due to assumptions in the coherency
59    # mechanism. Instead the latency is annotated on the packet and
60    # left to the neighbouring modules.
61    #
62    # A request incurs the frontend latency, possibly snoop filter
63    # lookup latency, and forward latency. A response incurs the
64    # response latency. Frontend latency encompasses arbitration and
65    # deciding what to do when a request arrives. the forward latency
66    # is the latency involved once a decision is made to forward the
67    # request. The response latency, is similar to the forward
68    # latency, but for responses rather than requests.
69    frontend_latency = Param.Cycles(3, "Frontend latency")
70    forward_latency = Param.Cycles(4, "Forward latency")
71    response_latency = Param.Cycles(2, "Response latency")
72
73    # Width governing the throughput of the crossbar
74    width = Param.Unsigned(8, "Datapath width per port (bytes)")
75
76    # The default port can be left unconnected, or be used to connect
77    # a default slave port
78    default = MasterPort("Port for connecting an optional default slave")
79
80    # The default port can be used unconditionally, or based on
81    # address range, in which case it may overlap with other
82    # ports. The default range is always checked first, thus creating
83    # a two-level hierarchical lookup. This is useful e.g. for the PCI
84    # xbar configuration.
85    use_default_range = Param.Bool(False, "Perform address mapping for " \
86                                       "the default port")
87
88class NoncoherentXBar(BaseXBar):
89    type = 'NoncoherentXBar'
90    cxx_header = "mem/noncoherent_xbar.hh"
91
92class CoherentXBar(BaseXBar):
93    type = 'CoherentXBar'
94    cxx_header = "mem/coherent_xbar.hh"
95
96    # The coherent crossbar additionally has snoop responses that are
97    # forwarded after a specific latency.
98    snoop_response_latency = Param.Cycles(4, "Snoop response latency")
99
100    # An optional snoop filter
101    snoop_filter = Param.SnoopFilter(NULL, "Selected snoop filter")
102
103    system = Param.System(Parent.any, "System that the crossbar belongs to.")
104
105class SnoopFilter(SimObject):
106    type = 'SnoopFilter'
107    cxx_header = "mem/snoop_filter.hh"
108
109    # Lookup latency of the snoop filter, added to requests that pass
110    # through a coherent crossbar.
111    lookup_latency = Param.Cycles(1, "Lookup latency")
112
113    system = Param.System(Parent.any, "System that the crossbar belongs to.")
114