CGRA PnR

Generic place and route tool for CGRA.

Getting started

Prerequisites

Because the C++ implementation, exposed to Python via pybind11, uses lots of C++14/17 features, a modern C++ compiler is required.

• g++ 7.0+/clang 4.0+
• cmake 3.9 and above.
• Python 2.7+/3.6+

It also requires libigraph0-dev to be installed. On Ubuntu-based distros, simply do

sudo apt-get install libigraph0-dev

Install

$ git submodule update --init --recursive
$ pip install thunder/
$ pip install cyclone/
$ pip install -r requirements.txt

It also has C++ native binaries interface, to use them, simply do

$ ./install.sh

Use CGRA PnR in other projects

The placement engine, thunder, can be used outside this repo. Simply do

pip install pythunder

Usage of this library can be found in place.py.

The routing engine, cyclone, can also be used outside this repo. Simply do

pip install pycyclone

By default PyPI will have the latest release version of binary wheels for linux systems. This is built through manylinux build here

Usage

$ ./scripts/pnr_flow.sh [--no-reg-fold] <cgra_info.txt> <mapped_design.json> [output.bsb]

• --no-reg-fold optimizes for the routing path as it turns some registers into PE tiles. Without using --no-reg-fold we will have about 15% area reduction, but it may have longer path, based on the current CGRA design. So given timing information as well as more flexible hardware generation in the future, this option needs to be used on a case by case basis.
• if <output.bsb> not specified, it will output <mapped_design.bsb> to the same directory as <netlist.json>

Files created in the same directory as <mapped_design.json>:

• <mapped_design.n2v>: random walk on the star-expanded netlist graph
• <mapped_design.emb>: netlist embedding computed by word2vec
• <mapped_design.packed>: packed netlists, including information on converted netlist as well as id information used internally throughout the toolchain.
• <mapped_design.place>, placement result, using internal id
• <mapped_design.route>, routing result. Each section is the route for a single net. More details see the header section in the result file
• <mapped_design.bsb, bsbuilder files can be compiled to bitstream via bsbuilder.py in CGRAGenerator

Analysis Tool

The toolchain has a tool to produce post-PnR report on area usage, route channel usage, and timing. Here is an example on harris:

Area Usage:
I    █                                                                   2.94%
P    ██████████████████████████                                          39.58%
M    ██████████                                                          15.62%
--------------------------------------------------------------------------------
Total wire: 530
--------------------------------------------------------------------------------
Critical Path:
Delay: 9.75 ns Max Clock Speed: 102.56 MHz
MUL  ███████████████████████████                                         41.03%
SB   █████████████████████                                               32.31%
ALU  ██████████████████                                                  26.67%
CB                                                                       0.00%
MEM                                                                      0.00%
REG                                                                      0.00%
--------------------------------------------------------------------------------
BUS: 16
TRACK 0 ████████████████                                                 24.38%
TRACK 1 █████████████                                                    20.44%
TRACK 2 █████████                                                        14.10%
TRACK 3 ████████                                                         12.47%
TRACK 4                                                                  0.85%
BUS: 1
TRACK 0 █████                                                            8.56%
TRACK 1 █                                                                1.92%
TRACK 2                                                                  0.00%
TRACK 3                                                                  0.00%
TRACK 4                                                                  0.00%

FPGA

It supports both VPR and bookshelf format. As a result, it can place any packed version of VPR benchmark or ISPD FPGA benchmark. However, because it's not designed to place generic netlists, it may not obtain an optimal solution, or may be very slow to converge.