6.2. SoCs with NoC-based Interconnects
The primary way to integrate a network-on-chip into a Chipyard SoC is to map one of the standard TileLink crossbar-based buses (System Bus, Memory Bus, Control Bus, etc.) to a Constellation-generated NoC.
The interconnect can be mapped as a “private” interconnect for the TileLink bus, in which case a dedicated interconnect to carry the bus traffic will be generated. Alternatively, the interconnect can be mapped to a shared global interconnect, in which case multiple TileLink buses can be transported over a single shared interconnect.
6.2.1. Private Interconnects
An example of integrating dedicated private interconnects for the System Bus, Memory Bus, and Control Bus can be seen in the MultiNoCConfig
of generators/chipyard/src/main/scala/config/NoCConfigs.scala.
class MultiNoCConfig extends Config(
new constellation.soc.WithCbusNoC(constellation.protocol.SimpleTLNoCParams(
constellation.protocol.DiplomaticNetworkNodeMapping(
inNodeMapping = ListMap(
"serial_tl" -> 0),
outNodeMapping = ListMap(
"error" -> 1, "ctrls[0]" -> 2, "pbus" -> 3, "plic" -> 4,
"clint" -> 5, "dmInner" -> 6, "bootrom" -> 7, "clock" -> 8)),
NoCParams(
topology = TerminalRouter(BidirectionalLine(9)),
channelParamGen = (a, b) => UserChannelParams(Seq.fill(5) { UserVirtualChannelParams(4) }),
routingRelation = NonblockingVirtualSubnetworksRouting(TerminalRouterRouting(BidirectionalLineRouting()), 5, 1))
)) ++
new constellation.soc.WithMbusNoC(constellation.protocol.SimpleTLNoCParams(
constellation.protocol.DiplomaticNetworkNodeMapping(
inNodeMapping = ListMap(
"L2 InclusiveCache[0]" -> 1, "L2 InclusiveCache[1]" -> 2,
"L2 InclusiveCache[2]" -> 5, "L2 InclusiveCache[3]" -> 6),
outNodeMapping = ListMap(
"system[0]" -> 0, "system[1]" -> 3, "system[2]" -> 4 , "system[3]" -> 7,
"serial_tl_0" -> 0)),
NoCParams(
topology = TerminalRouter(BidirectionalTorus1D(8)),
channelParamGen = (a, b) => UserChannelParams(Seq.fill(10) { UserVirtualChannelParams(4) }),
routingRelation = BlockingVirtualSubnetworksRouting(TerminalRouterRouting(BidirectionalTorus1DShortestRouting()), 5, 2))
)) ++
new constellation.soc.WithSbusNoC(constellation.protocol.SimpleTLNoCParams(
constellation.protocol.DiplomaticNetworkNodeMapping(
inNodeMapping = ListMap(
"Core 0" -> 1, "Core 1" -> 2, "Core 2" -> 4 , "Core 3" -> 7,
"Core 4" -> 8, "Core 5" -> 11, "Core 6" -> 13, "Core 7" -> 14,
"serial_tl" -> 0),
outNodeMapping = ListMap(
"system[0]" -> 5, "system[1]" -> 6, "system[2]" -> 9, "system[3]" -> 10,
"pbus" -> 3)),
NoCParams(
topology = TerminalRouter(Mesh2D(4, 4)),
channelParamGen = (a, b) => UserChannelParams(Seq.fill(8) { UserVirtualChannelParams(4) }),
routingRelation = BlockingVirtualSubnetworksRouting(TerminalRouterRouting(Mesh2DEscapeRouting()), 5, 1))
)) ++
new freechips.rocketchip.rocket.WithNBigCores(8) ++
new freechips.rocketchip.subsystem.WithNBanks(4) ++
new freechips.rocketchip.subsystem.WithNMemoryChannels(4) ++
new chipyard.config.AbstractConfig
)
Note that for each bus (Sbus
/ Mbus
/ Cbus
), the configuration fragment provides both a parameterization of the private NoC, as well as a mapping between TileLink agents and physical NoC nodes.
For more information on how to construct the NoC parameters, see the Constellation documentation.