SPACX hybrid Network on Chip (NoC) Simulation

This project simulates the Optical plus Electrical Network on Chip (NoC) architecture SPACX using SystemC TLM 2.0

Prerequisites

• SystemC (version 2.3.3 or later)
• C++ compiler supporting C++17 or later (e.g., GCC 7+ or Clang 5+)
• Make

Setup

1. Install SystemC on your system.

2. Set the SYSTEMC_HOME environment variable to point to your SystemC installation directory:

   export SYSTEMC_HOME=/path/to/your/systemc/installation
   
   

Compilation

make

Output

./out/simulation

or

make run

Project directory structure

SPACX

• src
  • GB
    • Global_Buffer.h
    • Global_Buffer.cpp
  • Interposer
    • Interposer_Interface.h
    • Interposer_Interface.cpp
  • Chiplet
    • Chiplet_Interface.h
    • Chiplet_Interface.cpp
  • Optical_Electrical
    • O_E_converter.h
    • O_E_converter.cpp
  • PE
    • Processing_Element.h
    • Processing_Element.cpp
  • Utils
    • configuration.h
    • noc_logger.h
    • noc_logger.cpp
    • token_manager.h
• scripts
  • input_feature.py
  • weight_kernal.py
• out
• obj
• main.cpp
• Makefile
• README.md

Log files

The log files are in

• out/report.log : general communication like token transfer
• out/gb_comm.log : communication to and from global buffer
• out/interposer_comm.log : communication to and from interposer interface
• out/chiplet_comm.log : communication to and from chiplet interface
• out/oec_comm.log : communication to and from OEC
• out/pe_comm.log : communication to and from PE

SPACX initial implementation

• The Global Buffer is initializing all the transactions
• In the beggining GB generates weights and input features as matrices and convert them to payloads
• The GB is connected to interposer interface to accept the payload through TLM blocking communication
• The address is the wavelegth, which is encoded into the payload and transmitted
• The interposer interface simply diverts the payload to chiplet interface again as TLM blocking communication
• The chiplet interface is connected to all PEs in a chiplet through the optical to electrical converter
• The chiplet interface copies the data to the curresponding OEC based on the address that is the wavelength
• Once the data is in the OEC, they are simply forwarding them to the PEs using the TLM blocking communication
• In PEs the data is stored into 2 fifos, the weight buffer and the buffer for input features
• The PE then multiplies it and gets the Psum stored into the accumulation buffer
• once the psum is ready, PE weights for the token, and then gives the data to the OEC
• OEC then transfers the data to the chiplet interface, and then to interposer interface in backward
• This way the Psums are back at global buffer through multiple TLM blocking transport

SPACX architecture and its operation

1. SPACX Overview: SPACX leverages photonic interconnects for efficient data communication in chiplet-based architectures, focusing on the needs of DNN inference, such as broadcast communication. It uses a hierarchical design:

• Global waveguide: Connects all chiplets.
• Local waveguide: Exists within each chiplet for intra-chiplet communication.

2. Key Components: Chiplets and Processing Elements (PEs):

• Each chiplet has multiple PEs (e.g., 8 per chiplet in the example).
• PEs perform computations like Multiply-and-Accumulate (MAC) for DNN workloads.
• Each PE has:
  • Two receivers for incoming broadcast data (local and global).
  • One transmitter for sending computed results back to the global buffer (GB). Wavelengths and Waveguides:
• Data transmission uses wavelength-division multiplexing (WDM).
• Wavelength allocation:
  • Global (cross-chiplet) wavelengths: Used for broadcasting the same data to corresponding PEs across all chiplets.
  • Local (single-chiplet) wavelengths: Used for intra-chiplet broadcasts and communication between chiplet PEs and the GB. Optical Splitters and Filters:
• Optical splitters: Split light (data) across multiple destinations by controlling the split ratio. Used for broadcasts.
• Optical filters: Select or forward specific wavelengths for targeted communication.

3. Communication Mechanisms: A. Cross-Chiplet Broadcast (Global Waveguide):

• Example: Data for PE0 across all chiplets is sent using wavelength λ0.
• Process:
  • The GB modulates data onto λ0.
  • Splitters in the global waveguide distribute power to each chiplet's local waveguide.
  • Local waveguides deliver the data to PE0 on each chiplet. B. Single-Chiplet Broadcast (Local Waveguide):
• Example: Data for all PEs within a single chiplet (e.g., Chiplet0) is sent using wavelength λ8.
• Process:
  • The GB modulates data onto λ8.
  • Optical filters direct all power of λ8 from the global waveguide to the local waveguide.
  • Splitters on the local waveguide evenly distribute data to all PEs within Chiplet0. C. PE-to-GB Communication:
• Each chiplet's PEs share a single wavelength for sending computed results back to the GB (e.g. λ8 for Chiplet0).
• Token-based arbitration ensures orderly transmission:
  • A token is passed sequentially among PEs, granting transmission access to one PE at a time.