Implementation of a RISC-V processor using the Synopsys Digital Design Flow

Here is the updated index for your README.md:

Table of Contents

0. Synopsys Digital Design Flow
1. Specification
2. RTL: Cell description coding
3. Console: Syntax Check
4. VCS: Logic simulation
5. Logic Synthesis
6. Formal Verification
7. Pre-Layout STA (Prime Time)
8. Floorplanning, placement & Routing
9. Physical Verification
10. Post-Layout STA (Prime Time)
11. Finished Design
12. Extra - RVSCC by MARIO
    • RTL
    • Logic Simulation
    • Logic Synthesis
    • Floorplan
13. Extra - Windows 10/11 Synopsys Server Connection
    • MobaXterm Connection
    • RSA Key Generation - Needed for SSH Connection with VSC
    • Save RSA Public Key at Synopsys Server
    • Install and run Xlaunch
    • VSCode SSH connection
14. References

Synopsys Digital Design Flow

The Digital Design Flow is the following

Specification

Design of a RISC-V processor. Implementation of an RV32I processor with a five-stage pipeline.

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Diseño de un procesador RISC-V. Implementación de procesador RV32I con pipeline de cinco etapas:

Implementar un procesador RISC-V sencillo. En este caso el desafío no estaría tanto en el diseño en si, ya que hay varios que han implementado y verificado sus propias versiones de procesador en HDL. La idea es que teniendo un código base medianamente probado, el esfuerzo se enfoque en documentar el flujo de diseño en las capas más bajas de la implementación. El ya tener un RISC-V como base abre las puertas para posteriores proyectos que integren diversos periféricos.

No se plantea el uso de FPGAs como un objetivo de los proyectos que desarrollaran los estudiantes. Se mencionaron las FPGAs en el contexto de que todos los participantes tienen experiencia en distintos grados en el flujo de diseño para FPGAs (algunos bien avanzados), por lo que la idea es justamente que extrapolen esa experiencia en las etapas de síntesis para preparar una actividad que muestre el flujo de diseño para un ASIC.

RTL: Cell description coding

• Tests for a simple ALU, an adder, and other descriptions can be found in the test_code folder, with the aim of testing the design flow preliminarily.

• The description of a unicycle processor for testing the design flow can be found in the Unicycle folder.

• It is expected later to have a folder with the description of the RV32I processor.

Console: Syntax Check

The command vlogan <file(s)> -full64 –sverilog +v2k gives a syntax error in the simulation part using SystemVerilog, so we opted for the following command:

vcs -sverilog -parse_only <archivo(s)>

Which checks the syntax and does not generate the simulation file \sim typical of the vcs command.

VCS: Logic simulation

To start a simulation we run in the console the following command:

vcs -sverilog -debug -cpp -gcc -R -gui <achivo(s)>

Where -R runs the simulation (which should be added to the files as a testbench) immediately after compilation.

Other options for the VCS command are:

Opciones de vcs
-debug	Enable debug capabilities
-debug_all	Enable source-line debugging
-debug_pp	Debug post-processing
-gui	Start DVE after compilation finishes
+define	Defines macro in the verilog source
-l	Create log file
-o <sim_name>	Rename simulation executable
-ucli	Enable Tcl command-line interface
-R	Run simulation immediately after compile
-cm	Enable coverage options

If you want to run the simulation without running vcs again, you can do it using the following command:

./simv <options> 

Where you may use the following options:

Opciones de ./simv
-ucli	Stop at Tcl prompt upon start-up
-i <run.tcl>	Execute specified Tcl script upon start-up
-l	Create runtime logfile
-gui	Start interactive GUI session
-xlrm	Allows relaxed/non-LRM compliant code
-cm	Enable coverage options
-cm_name	Give name to the test (default is test)

Logic Synthesis

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obs:

Make sure to download the skywater library, for this, we have all the files you might need here: https://drive.google.com/drive/folders/1yW7nUxN1jMjz_ce_J53yK2rmMj6R_uhI?usp=sharing. Add the content to the sky130_fd_sc_hd folder.

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Run the Makefile that runs the logic_synthesis.tcl script in the logic_synthesis folder.

cd logic_synthesis
make

As a result, it displays information in the console, as well as data regarding timing, area, power, etc in the logic_synthesis/report folder.

To clean all the log files, and maintain the reports, do a make clean.

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Pending tasks

• Verify the results of the logic synthesis for the Unicycle or another simple description, especially the reported WNS.

Formal Verification

For formal verification we use the formality tool. It is important to check if you have access to this, as with the prime time tool, for this make sure that the following lines are found in .bashrc at the synopsys server:

PATH=/home/SynopsysSoftware/fm/R-2020.09-SP5/bin:$PATH     
PATH=/home/SynopsysSoftware/prime/R-2020.09-SP5-3/bin:$PATH

Once we have access to the tool, we can start the gui in the console with the following command:

formality

In the gui we follow the following steps:

• Cargar el RTL en la pestaña 1. Ref:

• Cargar la Netlist resultante de la sintesis logica en los pasos anteriores en 2. Impl.:

• Match y Verificacion:

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obs:

• For now, there are some WARNINGS regarding the unicicle's imem and dmem code, so the tutorial is based on a simple alu.
• In the Overleaf there is some instructions in how to make the formal verification without GUI.

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Status: Elaborating design imem ...
Warning: Index may take values outside array bound, may cause simulation mismatch .. (Signal: RAM Block: /imem File: /home/usuario12/RISC-V/Uniciclo/imem.sv Line: 9) (FMR_ELAB-147) Status: Elaborating design dmem ...
Warning: Index may take values outside array bound, may cause simulation mismatch .. (Signal: RAM Block: /dmem File: /home/usuario12/RISC-V/Uniciclo/dmem.sv Line: 8) (FMR_ELAB-147)

Pre-Layour STA ( Prime Time )

Text

Floorplanning, placement & Routing

Floorplan:

Run using the Makefile in the icc2 folder, that runs the icc2_test.tcl script.

cd icc2
make

To clean all the log files, do a make clean.

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obs: Por el momento tenemos los siguientes problemas:

• icc2: no se pueden hacer operaciones de optmizacion como place_opt, clock_opt ni route_opt.
• icc2: no existen los pines de salida de vcc ni vdd, no sabemos porque.
• formality: No es posible setear el top del codigo de uniciclo, error de index may take values oustide array bound en dmem e imem

Physical Verification

Text

Post-Layout STA ( Prime Time )

Text

Finished Design

Text

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Extra - RVSCC by MARIO

RTL

You can find the RTL in the rvscc folder. You can find the source code here: https://git.1159.cl/Mario1159/RVSCC

Logic Simulation

To run the logic simulation use the following:

vcs -sverilog -debug -cpp -gcc -R -gui timescale.sv rv32i_defs.sv test_five_stage_pipeline_core.sv alu_decoder.sv alu.sv cache_memory.sv control_unit.sv data_memory_if.sv data_memory.sv five_stage_pipeline_datapath.sv hazard_unit.sv imm_extend.sv instr_memory_if.sv instr_memory.sv jump_control.sv main_decoder.sv pipelined_control_unit.sv priority_encoder.sv register_file.sv

Note, if you want to run the Testbench rvscc/test_five_staged_pipeline_core.sv of this project, you need to uncomment the following static functions:

• check_fw_test_core_assertions in rvscc/data_memmory_if.sv in line 28.
• next_instr in rvscc/instr_memory_if.sv in line 15.

Logic Synthesis

Note that you need to comment all the static functions for the synthesis to run.

you might run the code in logic_synthesis folder, remember to the analyze and elaborate options in the first lines of logic_synthesis/logic_synthesis.tcl as follows:

analyze -format sverilog {../rvscc/timescale.sv ../rvscc/rv32i_defs.sv ../rvscc/alu_decoder.sv ../rvscc/alu.sv ../rvscc/cache_memory.sv ../rvscc/control_unit.sv ../rvscc/data_memory_if.sv ../rvscc/data_memory.sv ../rvscc/five_stage_pipeline_datapath.sv ../rvscc/hazard_unit.sv ../rvscc/imm_extend.sv ../rvscc/instr_memory_if.sv ../rvscc/instr_memory.sv ../rvscc/jump_control.sv ../rvscc/main_decoder.sv ../rvscc/pipelined_control_unit.sv ../rvscc/priority_encoder.sv ../rvscc/register_file.sv}
elaborate five_stage_pipeline_datapath

Change the name of the reports as needed, as example, in line 67:

## Save Design
write_file -format ddc -hierarchy -out report/rvscc.ddc
write_file -format verilog -hierarchy -out report/rvscc.v
write_sdc report/rvscc.sdc

Then you can use make in the terminal, being inside the logic_synthesis folder, and it will save the reports for the followings steps of the design in the logic_synthesis/report folder.

Floorplan

Use the scripts in scripts_compilation as always...

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OpenRAM - SRAM Compilation

Setup

We follow the OpenRAM documentation where we proceed with the steps:

Clone the repository

Install miniconda using the script included in the repository:

./install_conda.sh

and activate it with source ./miniconda/bin/activate.

As we are using Sky130, you must install open_pdk, and OpenRAM allows you to do it with:

cd $HOME/OpenRAM
make pdk

Then, install OpenRAM with:

cd $HOME/OpenRAM
make install

Check the environment variables in the setpaths.sh file, which is similar to:

#!/bin/bash

export OPENRAM_HOME="$HOME/OpenRAM/compiler"
export OPENRAM_TECH="$HOME/OpenRAM/technology"
export PDK_ROOT="$HOME/OpenRAM/open_pdks/sky130"
export PYTHONPATH=$OPENRAM_HOME

Set the environment variables with source setpaths.sh.

Usage

You can find the basic usage of OpenRAM in the same documentation, but in summary:

Once the setup is done and with source ./miniconda/bin/activate and source setpaths.sh active, you can run OpenRAM in the following script:

python3 $OPENRAM_HOME/../sram_compiler.py myconfig_sky130_32.py

where myconfig_sky130_32.py, a file found in openram/myconfig_sky130_32.py, describes a singleport SRAM of 32 words, 32 bits each.

Note

We encountered some issues with OpenRAM:

• To utilize tech_name = "sky130A" in the myconfig_sky130_32.py file, it was necessary to modify line 614 in compiler/characterizer/simulation.py by adding an A, as shown below:

# FIXME: change to a solution that does not depend on the technology
 if OPTS.tech_name == "sky130A" and len(self.all_ports) == 1:

• Had to be aware of the naming and PATH of OpenRAM (NO openram) to be at $HOME/OpenRAM.

• Be aware, there are extra ports that OpenRAM generates for no reason. for the tool to actually generate the SRAM for the sky130 tec we had to use the single port config where those lines are a must.

num_spare_rows = 1
num_spare_cols = 1

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SRAM setup

OpenRAM generates a variety of files when creating memory, which we need to use to generate other files of interest:

db file

To create the .db files required for the logical synthesis of the processor, we take the .lib files generated by OpenRAM and convert them using Library Compiler within the Synopsys server:

 > lc_shell

lc_shell> read_lib sram_32_32.lib
lc_shell> write_lib sram_32_32_lib -format db -output sram_32_32.db
lc_shell> exit
> 

Now, we can link it to the library just like with the other .db files in logic_syntesis.tcl.

ndm file

Para generar los archivos .ndm, necesitamos el archivo de la tecnologia sacado de la biblioteca de sky130 para poder crear una nueva libreria con el siguiente comando usando dentro de lc_shell

To generate .ndm files, we need the technology file from the sky130 library to create a new library with the following command in lc_shell:

 > lc_shell
lc_shell> create_physical_lib  -technology skywater130_fd_sc_hd.tf physucal_lib_name

Then we save it with:

lc_shell> write_physical_lib

This will likely produce the error UIL-201 (error) None of the cells have FRAM view! which we can resolve with:

lc_shell>  create_frame

We repeat:

lc_shell>  write_physical_lib

This should return ... wrote physical library physucal_lib_name.ndm

Finally, with the .ndm file, we can utilize the SRAM in ICC2 for placing and routing.

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EXTRA - WINDOWS 10/11 SYNOPSYS SERVER CONNECTION

MobaXterm Connection

• algun dia lo explico si es necesario para ser auto contenido...

RSA Key Generation - Needed for SSH Connection with VSC

• Open cmd and type ssh-keygen -t rsa -b 2048
• If it's your first time generating a key, you can use the default file to save the key
• passphrase can be let empty
• now the public and private key are (usually) saved at C:\Users\<user_name>\.ssh\

Save RSA Public Key at Synopsys Server

• Enter the server (using your username and password given)
• once there, go to the .ssh folder and create the authorized_keys file, open it and paste the content of the id_rsa.pub created earlier

Install and run Xlaunch

• Install VcXsrv Windows X Server (https://sourceforge.net/projects/vcxsrv/)
• run it with default options

VSCode SSH connection

• Install Remote -SSH, Remote X11 and Remote X11 (SSH) extension in VSC

• Open command palette > Remote-SSH: Open SSH Configuration File.. > .../.ssh/config

• Edit it as follows:

  Host SynopsysRemote
        HostName ****.****.****.****
        Port 22
        User usuarioXX
        IdentityFile C:\Users\<user_name>\.ssh\id_rsa
        ForwardAgent yes
        ForwardX11 yes
        ForwardX11Trusted yes
        XAuthLocation "C:\Program Files\VcXsrv\xauth.exe"
  

• In VSC Settings, be sure that Remote X11.SSH: Private Key is set as the IdentityFile from the previous step

• In VSC Settings, be sure to have Remote X11.SSH: XAuth Permission Level as trusted

• In VSC Settings be sure to have Remote X11.SHH: Enable selected.

References

• VSC X11 SSG connection: https://github.com/microsoft/vscode-remote-release/issues/4600#issuecomment-791332086

• RSA key generation and linking to VSC: https://www.youtube.com/watch?v=PDVnUErS_us

• Formality tutorial: https://www.youtube.com/watch?v=CFRqPnqifx0

• ICC tutorial: https://www.youtube.com/watch?v=BQxG3jzcifg

• Five Stage Pipeline RISC-V by Mario - RVSCC: https://git.1159.cl/Mario1159/RVSCC

• SRAM Generators fixes: https://cornell-ece5745.github.io/ece5745-tut8-sram/

• OpenmRAM: https://github.com/VLSIDA/OpenRAM