Automatic Clockgate Generator

Required Packages:

How To Run:

python3 project3.py <netlist>

For instance, to create a clock-gated netlist for the provided 32bit register test case:

 python3 project3.py tests/32bits/test_32bit.gl.v

This will generate the file tests/32bits/test_32bit.gl.clockgate.v

Description

The program scans a netlist for pre-defined multiplexer templates that feed back a flipflop's output to itself. Once such a multiplexer is found, it is replaced with a clock gate and the multiplexer's data input is connected directly to the flip flop.

Multiplexer templates are divided into two main types:

Single Cells: These are cells that function as multiplexers on their own. (Ex: sky130_fd_sc_hd__mux2_1)
Multiple Cells: These are cells that function as multiplexers in combination with other cells.

Cell Templates

This is a list of register and multiplexer cells/templates recognized by the script:

Registers:

sky130_fd_sc_hd__dfxtp_1
sky130_fd_sc_hd__dfxtp_2
sky130_fd_sc_hd__dfxtp_4
sky130_fd_sc_hd__dfrtp_1

Multiplexer (Single Cell):

sky130_fd_sc_hd__mux2_1

Multiple (Multiple Cells):

sky130_fd_sc_hd__a21oi_1 combined with a sky130_fd_sc_hd__nor2_1 (An Inverter is connected to the Data input here, as a21oi takes in inverted data)

Algorithm

Search for all flipflops in the netlist and store them in a dictionary (marked by each flipflop's output wire)
Search for all single cell multiplexers. If one is found that has a flipflop's output wire as input, remove the mux and replace it with a clockgate, connecting the mux's data input directly to the flipflop.
Search for the first cell in each multiple-cell multiplexer template. If one is found, search for the second cell, etc... until the last cell is found. If the last cell has an input wire that is a flipflop's output wire, remove all the cells associated with the current multiplexer and replace it with a clockgate, connecting the data input (and inverters if required) directly to the flipflop.

Adding Clockgates

Each clockgate is associated with an enable wire, and there is only one clockgate for each enable wire. When a mux is replaced with a clockgate, it is checked first if there exists a clockgate associated with the mux's enable. If it exists, simply connect the found clockgate to the clock of the flipflop. If no such clockgate is found, create a new clockgate and associate it with the enable wire. A counter is kept for the number of flipflops connected to each clockgate. Depending on the value of this counter, the size of the clockgate varies in the following manner:

n <= 8: sky130_fd_sc_hd__dlclkp_1
n <= 16: sky130_fd_sc_hd__dlclkp_2
n > 16: sky130_fd_sc_hd__dlclkp_4

Where n is the number of load flipflops.

Using Different Standard Cell Libraries

To use a different library than Sky130, simply add the module names and ports of the clockgates, flipflops, single-cell muxs, multiple-cell muxs, and inverters to the following dictionaries in project3.py, respectively:

clock_gate
registers
muxs
gatemux
inv

Code Structure

├── project3.py 						(main file)
├── synthesis                           (contains files used for synthesis) 													
├── tests								
│   ├── 32bits				            (32bit test case)			
│   │    ├── test_32bit.v						
│   │    ├── test_32bit.tb.v							
│   │    ├── test_32bit.gl.v
│   │    ├── test_32bit.gl.clockgated.v				
│   ├── 16bits				            (16bit test case)			
│   │    ├── test_16bit.v						
│   │    ├── test_16bit.tb.v							
│   │    ├── test16_bit.gl.v
│   │    ├── test16_bit.gl.clockgated.v
│   ├── async_rst			            (test case with async reset)				
│   │    ├── test3.v						
│   │    ├── test3_tb.v							
│   │    ├── test3.gl.v
│   │    ├── test3.gl.clockgated.v       		
│   ├── test1			            (test case with a21oi)				
│   │    ├── test1.v						
│   │    ├── test1_tb.v							
│   │    ├── test1.gl.v
│   │    ├── test1.gl.clockgated.v       		
│   ├── test2			            (test case with 2 selectors)				
│   │    ├── test2.v						
│   │    ├── test2_tb.v							
│   │    ├── test2.gl.v
│   │    ├── test2.gl.clockgated.v

nyuriumuri / Automatic-Clock-Gating