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3. SoCIN Architecture
SoCIN [ZEF 03] is a NoC developed at Federal University of Rio Grande do Sul (UFRGS). It uses a 2-D mesh topology, where each router is addressed by a pair of coordinates (see Fig. 1). The first router of SoCIN was named RASoC (Router Architecture for SoC). Current router is named ParIS (Parameterizable Interconnect Switch) and was developed at University of Vale do Itajaí (Univali) [ZEF 04]. It is a soft-core with several parameters which allow generating SoCIN instances based on different configuration of its design space.
0,0 1,0 2,0 3,0
0,1 1,1 2,1 3,1
0,2 1,2 2,2 3,2
0,3 1,3 2,3 3,3
ParIS X,Y L
N
E
S W Y
3
2
1
0
0 1 2 3
X
Fig. 1 – SoCIN network and ParIS router
As shown in Fig. 1, each router has up to 5 communication ports. One of them is intended to be used as a terminal to attach a core (the Local port, or L), and the other ones (N, E, S and W) are used for connection with neighbor routers. Communication among cores attached to the network terminals is done by the means of packets of unlimited length. To be routed along the network, each packet must include the destination coordinates in a header. This information is used by each router in the packet path to determine the communication port to be used to forward the packet.
4. X Gsim architecture
X Gsim software architecture is composed by a visual integrated environment and a set of tools, originally presented in [ZEF 07]. X Gsim works with a SoC platform based on SystemC models of a router (ParIS), a traffic generator (named TG) and a traffic meter (named TM). ParIS router is modeled in SystemC RTL, and TG and TM are modeled in SystemC TL. A pair of TG-TM is attached at each network terminal and is responsible to inject packets into the network and to collect data for performance evaluation. X Gsim does the interface between user and its integrated tools, which are summarized below:
GNoC: it generates a SystemC RTL model of SoCIN (a network of ParIS instances);
GSoC: it generates a SystemC model of a SoC composed by SoCIN and instances of TM and TG;
GCC (C compiler): it is invoked to generate a system simulator based on the models generated by previous tools;
GTR: it configures the traffic pattern to be emulated by the network generators at the moment of a simulation experiment;
ATR: it analyses data collected by traffic meters and generates summary files used by X Gsim to show the performance metrics results to the user;
GNUPLOT: a GNU tool used to show the simulation results in a graphical format;
GTKWAVE: a GNU tool used to show waveforms with the packets sent and received at the network terminals.
For traffic modeling, the same model used in Atlas [TED 05] is applied. The major parameters for traffic generation used by GTR tool include: (i) bandwidth required by the flows; (ii) number of packets to be sent by each flow; (iii) spatial distribution used to define the destination of each flow; and (iv) type of injection rate.
They are available the following spatial distributions: uniform, non-uniform, local, complement, matrix transpose, perfect shuffle, and bit-reversal. The injection rate can be constant or variable. The last one includes five alternatives based on the variation of packet size, interval between packets, interval between arrivals, and
burst size. For variable injection rate, one can use one of three probability distributions: Normal, Exponential or Pareto On-Off.
In the development of X Gsim interface, they were used GTK+ and GLADE, a RAD (Rapid Application Development) framework for the development of visual interfaces based on GTK+ and GNOME. X Gsim was built to run over Linux systems.
X Gsim interface is organized in three tabs: Network configuration (Fig. 2.a), Traffic configuration (Fig. 2.b) and Network simulation (Fig. 3.a). The first two are used to enter the network and traffic parameters, respectively. The third one allow to configure a single or a multiple simulation experiment in order to evaluate performance of a single or multiple parameters set under one or more required bandwidths (see Fig 3.a). After simulation, the results can be seen in a text table presented in the message window (bottom area in Fig. 3.a), or in a graphical format (Fig. 3.b).
(a) (b) Fig. 2 – X Gsim interface: (a) Network configuration tab; (b) Traffic configuration tab.
(a) (b) Fig. 3 – X Gsim: (a) Network simulation tab; (b) graphical view
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5. Using X Gsim in NoC evaluation
This section presents examples of usage of X Gsim to compare the performance of different networks configurations. For the illustrated experiments bellow, the following parameters were fixed: (i) network size:
4 4; (ii) flit width: 30 bits; (iii) arbiter type: round-robin (RR); (iv) flow control technique: credit-based (CB);
(v) packet length: 16 flits; (vi) spatial distribution: non-uniform, (vii) traffic type: constant; (viii) required bandwidth: ranging from 10 to 100% of channel bandwidth (with increment of 10%); (ix) number of packets per flow: 1000. In the first experiment, whose results are summarized in Fig. 4.a, we set the input and output buffers depth to 4 and 0 flits, respectively and varied the routing algorithm (XY and WF). Results show that, for the selected network and traffic configurations, XY algorithm is able to accept more traffic than WF algorithm.
This occurs because WF is a partially adaptive algorithm and tends to concentrate traffic in the center of the network. In the second experiment, we set the routing algorithm to XY, and the output buffers depth to 0 (no buffer). Three input buffer depths were compared: 2, 4 and 16 flits. Results are summarized in Fig 4.b and show that, for the selected configurations, as deeper the input buffers are, more traffic is accepted by the network.
(a)
(b)
Fig. 4 – Experiments comparing: (a) XY and WF routing algorithms; and (b) 2-, 4-, and 16-flit buffers.
6. Conclusions
This paper presented an integrated environment for performance evaluation of NoCs by simulation using SystemC. This environment improved the usability of tools it integrates, because they were originally invoked by command line. Also, it automated the execution of multiple experiments. Compared to Atlas, X Gsim is different in the sense that simulation is done by using only SystemC models. In Atlas, the network is modeled in VHDL and the other components in SystemC. X Gsim has a major limitation regarding the lack of an interface to edit each flow independently from the others, and this feature will be added in a future work.
7. Acknowledgments
This work was supported by Art.170 research program of Santa Catarina State Governement.
8. References
[GUE 00] GUERRIER, P.; GREINER, A. A generic architecture for on-chip packet-switched interconnections. In:
DATE, 2000, Paris., IEEE CS Press, 2000. p. 250-256.
[MEL 07] MELLO, Aline V. de. Qualidade de serviço em redes intra-chip: implementação e avaliação sobre a rede Hermes. Dissertação de Mestrado, PPGCC-PUCRS, Porto Alegre, 2007.
[MOR 03] MORAES, F. et al. A low area overhead packet-switched Network-on-Chip: architecture and prototyping. In: IFIP WG 10.5 VLSI-SOC, 2003, Darmstadt, 2003. p. 318-323.
[TED 05] TEDESCO, L. P. Uma Proposta para Geração de Tráfego e Avaliação de Desempenho para NoCs, Dissertação de Mestrado, PPGCC-PUCRS, Porto Alegre, 2005.
[ZEF 03] ZEFERINO, C. A., SUSIN, A. A. : SoCIN: A Parametric and Scalable Network-on-Chip. In: SBCCI, 16, 2003, São Paulo, IEEE CS Press, 2003. p. 168-174.
[ZEF 04] ZEFERINO, C. A., SANTO, F. G. M. E., SUSIN, A. A. “Paris: A Parameterizable Interconnect Switch for Networks-on-Chip”, In: SBCCI, 17., 2004, Porto de Galinhas. Proceedings. ACM Press, 2004. p.
204-209.
[ZEF 07] ZEFERINO, C. A, BRUCH, J. V, PEREIRA, T. F, KREUTZ, M. E, SUSIN, A. A., “Avaliação de Desempenho de Redes em Chip Modelada em SystemC. In: WPERFORMANCE, 2007, Rio de Janeiro, SBC, 2007. p. 559-578.