README file that accompanies all generated networks.
In addition to this README file every generated network also comes with a minimal bare bones testbench to get you started.
/* ========================================================================= * * CONNECT - CONfigurable NEtwork Creation Tool * Copyright (c) 2012 by Michael K. Papamichael, Carnegie Mellon University * * ========================================================================= */ /////////////////////////////////// //-------- General info ----------- CONNECT is a flexible RTL generator for fast, FPGA-friendly Networks-on-Chip. This website serves as a front-end to CONNECT's network generation engine, which is primarily based on Bluespec System Verilog. All networks generated through CONNECT consist of fully synthesizable Verilog. CONNECT supports a variety of common network topologies, as well as custom user-specified networks. A variety of network and router parameters, such as router type, pipelining options, the number of virtual channels or allocator type, allow the user to further customize the network and trade-off between resource usage and performance. For license information please see the LICENSE file. ////////////////////////////////////////////////// //-------- Using the generated network ----------- All necessary files to implement a working network are located in this directory. For networks with credit-based flow control the top module is called "mkNetwork" and is located in the mkNetwork.v file. For networks with peek flow control the top module is called mkNetworkSimple and is located in the mkNetworkSimple.v file. Both the mkNetwork and mkNetworkSimple module interfaces consist of a set of ports used for sending and receiving flits and flow control information. The credit-based and peek-based networks share the same interface for sending and receiving flits, but offer different flow-control interfaces, which are detailed below. ////////////////////////////////////////////////////////////////////////////////// //-------- Data Send/Receive interface (mkNetwork and mkNetworkSimple) ----------- The mkNetwork credit-based interface consists of the following set of wires and buses for each port <P>: =================================== ==== Send Port Wires and Buses ==== =================================== - EN_send_ports_<P>_putFlit input wire: Assert when sending a flit to indicate send_ports_P_putFlit_flit_in carries valid data. - send_ports_<P>_putFlit_flit_in input bus, with the following fields: MSB LSB ------------------------------------------------------------------------ | <valid bit> | <is_tail> | <destination> | <virtual channel> | <data> | ------------------------------------------------------------------------ Field Info: <valid bit> : Indicates a valid flit. Set to 1 when sending a flit. <is_tail> : Indicates this is a tail flit, i.e. the last flit of a packet. Should be set to 1 for single-flit packets as they are also tail flits. <destination> : Specifies the destination of the current flit. Populate with a valid binary encoded router ID that corresponds to one of the routers in the network. <virtual channel> : For VC-based networks this field specifies the virtual channel to use and should be populated with a valid VC, depending on the number of available virtual channels. Lower VCs are prioritized over higher VCs. Networks that do not employ virtual channels (Virtual-Output-Queued and Input-Queued) essentially behave as if they only had a single virtual channel. As a result, for non-VC networks this field is 1-bit wide and should be set to 0. <data> : User data field. Populate with data to be transfered. //-------- Credit-based Flow Control Interface (mkNetwork) ----------- - EN_send_ports_<P>_getCredits input wire: indicates sender is ready to receive a credit. - send_ports_<P>_getCredits, output bus, with the following fields: MSB LSB ----------------------------------- | <valid bit> | <virtual channel> | ----------------------------------- Field Info: <valid bit> : Indicates a valid credit. <virtual channel> : Indicates the virtual channel that the incoming credit is for. For non-VC networks (VOQ and IQ) this field is 1-bit wide and should be set to 0. //-------- Peek-based Flow Control Interface (mkNetworkSimple) ----------- - EN_send_ports_<P>_getNonFullVCs input wire: indicates sender is ready to receive a credit. - send_ports_<P>_getNonFullVCs, output bus, that carries a bitmask indicating which VCs have available buffers space (i.e. are non Full). MSB corresponds to the highest VC and LSB corresponds to the lowest VC. For non-VC networks this signal is a single bit. ====================================== ==== Receive Port Wires and Buses ==== ====================================== - EN_recv_ports_P_getFlit input wire: Assert when ready to receive an incoming flit. - recv_ports_P_getFlit output bus, with the following fields: MSB LSB ------------------------------------------------------------------------ | <valid bit> | <is_tail> | <destination> | <virtual channel> | <data> | ------------------------------------------------------------------------ Field Info: <valid bit> : Indicates a valid flit. Check to see if received flit is valid. <is_tail> : Indicates this is a tail flit, i.e. the last flit of a packet. Should be set to 1 for single-flit packets as they are also tail flits. <destination> : Specifies the destination of the received flit. <virtual channel> : Specifies the virtual channel of the received flit. Ignore for non-VC networks <data> : User data field. Contains the transferred data. //-------- Credit-based Flow Control Interface (mkNetwork) ----------- - EN_recv_ports_P_putCredits input wire: indicates receiver is sending a credit. Assert when sending a credit. - recv_ports_P_putCredits_cr_in, input bus, with the following fields: MSB LSB ----------------------------------- | <valid bit> | <virtual channel> | ----------------------------------- Field Info: <valid bit> : Indicates a valid credit. <virtual channel> : Indicates the virtual channel that the outgoing credit is for. //-------- Peek-based Flow Control Interface (mkNetworkSimple) ----------- - EN_recv_ports_<P>_putNonFullVCs input wire: indicates sender is ready to receive a credit. - recv_ports_<P>_putNonFullVCs, input bus, which is a bitmask indicating which VCs have available buffers space (i.e. are non Full). MSB corresponds to the highest VC and LSB corresponds to the lowest VC. For non-VC networks this signal is a single bit. ====================================================== ==== Credit-based Flow Control - Credit Handling ==== ====================================================== For CONNECT-generated networks that use credit-based flow control network clients need to maintain and exchange flow control information (i.e. credits) with the routers they are connected to. - Outgoing traffic (sending flits as a client) Each client needs to maintain credit counters (one per VC) and a client should only send a flit into the network if the corresponding credit counter for the particular VC is non-zero. Credit counters should be initialized according to the selected Flit Buffer Depth (e.g. for a Flit Buffer Depth of 7, credit counters would need to be initialized to the value 7 after reset). Once the flit is injected into the network the client needs to decrement the number of available credits for the particular VC to keep track of remaining credits. - Incoming traffic (receiving flits as a client) Each client needs to maintain incoming flit buffers (one per VC) to store the flits it receives. These flit buffers need to be sized according to the selected Flit Buffer Depth (e.g. for a Flit Buffer depth of 7, the depth of the incoming flit buffers should be at least 7 entries deep). Each time the client dequeues a flit from one of its incoming flit buffers, it needs to send a credit for the corresponding VC to inform the router about the newly available space. Routers initially assume that they have enough credits to fill the client's incoming flit buffers. Note that if client is guaranteed to instantly consume every incoming flit, then it does not need to maintain incoming flit buffers; however it still has to provide a credit to the router for each incoming flit. ============================ ==== Peek Flow Control ==== ============================ CONNECT-generated networks that use Peek flow control offer a simpler interface. Instead of maintaing and exchanging credits, network clients simply need to check if the buffer they intend to inject into is not full by checking the send_ports_<P>_getNonFullVCs signal. In the case of VC-based networks they need to check the specific bit that corresponds to the VC that the flit belongs to.