# 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:

   ```bash
   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.