ASAP7_Digital-Design-Template

Introduction

This template repository is suited for digital design (OpenROAD flow-scripts) with the 7nm FinFET open-source ASAP7 PDK and the IIC-OSIC-Tools by IIC JKU.

ARM ASAP7 PDK: https://github.com/The-OpenROAD-Project/asap7 & https://www.sciencedirect.com/science/article/pii/S002626921630026X

IIC-OSIC-Tools: https://github.com/iic-jku/IIC-OSIC-TOOLS

The installation of IIC-OSIC-Tools is explained under ASAP7_Digital-Design-Template/doc/Docker-Tutorial.pdf or in this YouTube video: https://www.youtube.com/watch?v=azgFzleiBW8&t=1943s.

The recommended folder structure makes it easy to automate with shell scripts. VHDL files are read and converted into Verilog files (vhdl2verilog.sh). If Verilog files are available directly, this step can be skipped. With OpenROAD flow-scripts (ORFS) the newly generated Verilog file is synthesized and a layout is created. All these scripts are automated with run_all.sh and can be cleaned again with clean_all.sh. The template contains a 4-Bit counter with an enable input to get a better understanding of the structure and the file paths within the scripts.

I have also made a short video on how to use this repo: https://www.youtube.com/watch?v=UrUOg9s7gsM (video uses IHP's SG13G2 PDK)

If you want to use other OpenROAD-compatible PDKs, just add the corresponding files to the orfs/flow/platforms folder. These files can be found at https://github.com/The-OpenROAD-Project/OpenROAD-flow-scripts.

How to use this template for your design

Step-by-step introduction:

1. Download this repo and copy it into the foss/designs folder of your IIC-OSIC-Tools environment.
2. Rename the repo as you wish.
3. Execute clean_all.sh to remove any build files.
4. Add your VHDL code to the vhdl folder. It is advised that the same folder structure with rtl and sim is used.
5. Add your Xschem files and testbenches to the xschem folder
6. Adapt VHDL paths in vhdl2verilog.sh in the verilog folder. If the design is already done in Verilog, this step can be skipped. Do not forget to also comment out this step in run_all.sh.
7. Add config files to orfs/flow/designs/asap7. It is a good idea to copy an existing folder (e.g. counter_board) and adapt these files. Do not forget to set the path to the Verilog file in config.mk and set up the constraint.sdc and autotuner.json.
8. Adapt name and Verilog path in run_all.sh.

Hierarchical synthesis:

If you want to see the area per module / entity of your digital core, you can set export SYNTH_HIERARCHICAL=1 and export MAX_UNGROUP_SIZE=1 in run_all.sh and open the hierarchy browser in the OpenROAD GUI. If it is disabled, check the box under Windows/Hierarchy Browser.

Note that the mixed-signal simulation in Xschem will not work if SYNTH_HIERARCHICAL=1 is set. Hence, this line must be commented out for simulation.

Simulation details:

The VHDL code is simulated with GHDL & GTKWave (counter_tb.gtkw ) or Modelsim (sim.do). The VHDL simulation can be executed with simulate_vhdl.sh. The Verilog code is simulated with verilator & iverilog & GTKWave or Modelsim (sim_verilog_tb.do or sim_vhdl_tb.do). The Verilog simulation can be executed with simulate_verilog.sh. Alternatively, one can use Surfer instead of GTKWave. Further information can be found in the YouTube video.

Using hardened SRAM Macros

In order to use SRAM macros (or any other pre-hardened macros) during the flow, the OpenROAD flow needs to be aware of the respective files to use. In particular, the files needed are the GDS2, the LEF and the LIB files. These can be added in the config.mk Makefile by setting the variables ADDITIONAL_GDS, ADDITIONAL_LEFS and ADDITIONAL_LIBS respectively. Apart from setting these variables, the only requirement is to ensure that the respective component is instantiated in either the verilog or the transpiled VHDL code.

As an example, an SRAM macro was added for the ASAP7 node, with 1024 64-bit values (i.e. 64 bit data and 10 bits for addressing). The files for this macro can be found in orfs/flow/platforms/asap7/asap7_sram/0p0. They were originally taken from https://github.com/The-OpenROAD-Project/asap7_sram_0p0 and slightly adapted to ensure proper timing and layout. In this case, the SRAM is used by directly instantiating the properly named component srambank_256x4x64_6t122 as can be seen in sram.vhd. The name of this component must match the ones given in the GDS, LEF and LIB files in order for the flow to be able to match them up. The LEF and LIB files are text files, so inspecting them for the proper name is easy. However, for the GDS file, a viewer like KLayout is necessary. In KLayout for example, the name of the component is shown in the Cells window (View > Cells) and can also be changed there if necessary.