SCR1 RISC-V Core

SCR1 is an open-source and free to use RISC-V compatible MCU core, designed and maintained by Syntacore. It is industry-grade and silicon-proven (including full-wafer production), works out of the box in all major EDA flows and Verilator, and comes with extensive collateral and documentation.

Key features

Open sourced under SHL-license - unrestricted commercial use allowed
RV32I|E[MC] ISA
Machine privilege mode
<15 kGates in basic RV32EC configuration
2 to 4 stage pipeline
Optional IPIC with 16 IRQs
Optional RISC-V Debug subsystem with JTAG interface
32-bit AXI4/AHB-Lite external interface
Written in SystemVerilog
Optimized for area and power
3 predefined configurations
A number of fine-tuning options
Verification suite provided
Extensive documentation

For more information, see SCR1 External Architecture Specification and SCR1 User Manual.

Repository contents

Folder	Description
docs	SCR1 documentation
├─ scr1_eas.pdf	External Architecture Specification
└─ scr1_um.pdf	User Manual
src	SCR1 RTL source and testbench files
├─ includes	Header files
├─ pipeline	Pipeline source files
├─ core	Core top source files
├─ top	Cluster source files
└─ tb	Testbench files
sim	Tests and scripts for simulation
├─ tests/common	Common source files for tests
├─ tests/riscv_isa	Common source files for RISC-V ISA tests
├─ tests/riscv_compliance	Common source files for RISC-V Compliance tests
├─ tests/benchmarks/dhrystone21	Dhrystone 2.1 source files
├─ tests/benchmarks/coremark	Coremark platform specific source files
├─ tests/vectored_isr_sample	Simple test example for vectored interrupt mode
├─ tests/hello	Simple "hello" test
└─ verilator_wrap	Wrappers for Verilator simulation

SCR1 source file lists

SCR1 source file lists of SCR1 can be found in ./src:

core.files - all synthesized file sources of the SCR1 core
ahb_top.files - synthesized file sources of AHB cluster
axi_top.files - synthesized file sources of AXI cluster
ahb_tb.files - testbench file sources for AHB cluster (for simulation only)
axi_tb.files - testbench file sources for AXI cluster (for simulation only)

Library with header files to include is ./src/includes/

Simulation quick start guide

1. Prerequisites

RISC-V GCC toolchain is required to compile the software. You can use pre-built binaries or build the toolchain from scratch.

1.1. Using pre-built binary tools

Pre-built RISC-V GCC toolchain with support for all SCR1 architectural configurations is available for download from http://syntacore.com/page/products/sw-tools.

Download the archive for your platform: .tar.gz for Linux, .zip for Windows.
Extract the archive to your preferred directory <GCC_INSTALL_PATH>.
Add the <GCC_INSTALL_PATH>/bin folder to the $PATH environment variable:

    export PATH=<GCC_INSTALL_PATH>/bin:$PATH

1.2. Building tools from source

You can build the RISC-V GCC toolchain from sources, stored in official repo https://github.com/riscv/riscv-gnu-toolchain

Instructions on how to prepare and build the toolchain can be found on https://github.com/riscv/riscv-gnu-toolchain/blob/master/README.md

We recommend using the multilib compiler. Please note that RV32IC, RV32E, RV32EM, RV32EMC, RV32EC architectural configurations are not included in the compiler by default. If you plan to use them, you will need to include the appropriate libraries by yourself before building.

After the building, be sure to add the <GCC_INSTALL_PATH>/bin folder to the $PATH environment variable

2. Included tests

By default, the simulation package includes the following tests:

hello - simple "hello" program
riscv_isa - RISC-V ISA tests
riscv_compliance - RISC-V Compliance tests
dhrystone21 - Dhrystone benchmark
coremark - Coremark benchmark
vectored_isr_sample - test sample for vectored interrupts

Some of the tests depend on the selected architecture (e.g. rv32i|e base, supported extensions or IPIC), and therefore can not be used for all core configurations (these are skipped automatically).

Please, refer to SCR1 User Manual chapter "5.2. Test subset" for further details.

2.1. Prepare RISC-V ISA tests

Clone RISC-V ISA tests to your preferred directory <RISCV_TESTS_PATH>

    git clone https://github.com/riscv/riscv-tests
    cd riscv-tests
    git checkout a9433c4daa287fbe101025f2a079261a10149225

Set the $RISCV_TESTS environment variable accordingly:

    export RISCV_TESTS=<RISCV_TESTS_PATH>

2.2. Prepare RISC-V Compliance tests

Clone RISC-V Compliance tests to your preferred directory <RISCV_COMPLIANCE_TESTS_PATH>

    git clone https://github.com/riscv/riscv-compliance
    cd riscv-compliance
    git checkout 9f280717f26f50833357db9bfb77a8c79835f162

Set the $RISCV_COMPLIANCE_TESTS environment variable accordingly:

    export RISCV_COMPLIANCE_TESTS=<RISCV_COMPLIANCE_TESTS_PATH>

2.3. Prepare Coremark benchmark sources

Clone Coremark benchmark to your preferred directory <COREMARK_PATH>.

    git clone https://github.com/eembc/coremark

Copy the following files from the root of <COREMARK_PATH> into SCR1 directory ./sim/tests/benchmarks/coremark/src:

core_main.c
core_list_join.c
coremark.h
core_matrix.c
core_state.c
core_util.c

3. Running simulations

To build RTL, compile and run tests from the repo root folder:

    make run_<SIMULATOR> BUS=<AHB, AXI> ARCH=<I, IM, IMC, IC, E, EM, EMC, EC> IPIC=<0, 1>

By default, if not specified, the following parameters are used: BUS=AHB ARCH=IMC IPIC=0.

Build and run parameters can be configured in the ./Makefile.

After all the tests have finished, the results can be found in build/<SIM_CFG>/test_results.txt.

3.1. Simulator selection

Currently supported simulators:

run_modelsim - ModelSim by Mentor Graphics or Intel
run_vcs - Synopsys VCS
run_ncsim - Cadence NCSim
run_verilator - Verilator
run_verilator_wf - Verilator with waveforms support

Please note that RTL simulator executables should be in your $PATH variable.

For the run_verilator_wf option, a waveform is generated for all tests performed and saved in ./build/<SIM_CFG>/simx.vcd.

3.2. Architectural configuration

The RISC-V toolchain automatically uses the selected ARCH for code compilation.

If IPIC option is set to 1, then the test for vectored interrupts will be used in the simulation.

Please make sure that selected ARCH and IPIC matches architectural configuration of SCR1 RTL. Architectural parameters of SCR1 core can be configured in ./src/includes/scr1_arch_description.svh

SCR1 SDKs

FPGA-based SDKs are available at the https://github.com/syntacore/scr1-sdk.

Repo contains:

Pre-build images and open designs for several standard FPGAs boards:
- Digilent Arty (Xilinx)
- Digilent Nexys 4 DDR (Xilinx)
- Arria V GX Starter (Intel)
- Terasic DE10-Lite (Intel)
Software package:
- Bootloader
- Zephyr RTOS
- Tests\SW samples
User Guides for SDKs and tools

Contacts

Report an issue: https://github.com/syntacore/scr1/issues

Ask a question: scr1@syntacore.com

Chichichkin / scr1