Network test

This is a dummy cache coherence protocol that is used to operate the ruby network tester. The details about running the network tester can be found here.

Related Files

• src/mem/protocols
  • Network_test-cache.sm: cache controller specification
  • Network_test-dir.sm: directory controller specification
  • Network_test-msg.sm: message type specification
  • Network_test.slicc: container file

Cache Hierarchy

This protocol assumes a 1-level cache hierarchy. The role of the cache is to simply send messages from the cpu to the appropriate directory (based on the address), in the appropriate virtual network (based on the message type). It does not track any state. Infact, no CacheMemory is created unlike other protocols. The directory receives the messages from the caches, but does not send any back. The goal of this protocol is to enable simulation/testing of just the interconnection network.

Stable States and Invariants

States	Invariants
I	Default state of all cache blocks

Cache controller

• Requests, Responses, Triggers:
  • Load, Instruction fetch, Store from the core.

The network tester (in src/cpu/testers/networktest/networktest.cc) generates packets of the type ReadReq, INST_FETCH, and WriteReq, which are converted into RubyRequestType:LD, RubyRequestType:IFETCH, and RubyRequestType:ST, respectively, by the RubyPort (in src/mem/ruby/system/RubyPort.hh/cc). These messages reach the cache controller via the Sequencer. The destination for these messages is determined by the traffic type, and embedded in the address. More details can be found here.

• Main Operation:
  • The goal of the cache is only to act as a source node in the underlying interconnection network. It does not track any states.
  • On a LD from the core:
    • it returns a hit, and
    • maps the address to a directory, and issues a message for it of type MSG, and size Control (8 bytes) in the request vnet (0).
    • Note: vnet 0 could also be made to broadcast, instead of sending a directed message to a particular directory, by uncommenting the appropriate line in the a_issueRequest action in Network_test-cache.sm
  • On a IFETCH from the core:
    • it returns a hit, and
    • maps the address to a directory, and issues a message for it of type MSG, and size Control (8 bytes) in the forward vnet (1).
  • On a ST from the core:
    • it returns a hit, and
    • maps the address to a directory, and issues a message for it of type MSG, and size Data (72 bytes) in the response vnet (2).
  • Note: request, forward and response are just used to differentiate the vnets, but do not have any physical significance in this protocol.

Directory controller

• Requests, Responses, Triggers:
  • MSG from the cores

• Main Operation:
  • The goal of the directory is only to act as a destination node in the underlying interconnection network. It does not track any states.
  • The directory simply pops its incoming queue upon receiving the message.

Other features

• • This protocol assumes only 3 vnets.
  • It should only be used when running the ruby network test.