SARV is a 32-bit RISC-V processor based on the RV32I ISA. It currently supports the rv32iac_sstc_zaamo_zalrsc_zba_zbb_zbc_zbkc_zbs_zca_zcb_zicntr_zicond_zicsr_zihintpause_zihpm_zmmul ISA string, together with machine, supervisor, and user privilege modes.
The core is written in Verilog HDL and targets FPGA and ASIC implementations. It is designed as a compact embedded processor with a modular RTL architecture.
- Architectural & ABI Comparisons
- CSR & interrupts
- Critical Path
- Power Control
- Branch Prediction
- Return Address Stack
| Extension | Description | Status |
|---|---|---|
| RV32I | Base Integer Instructions | Full |
| Zmmul | Integer Multiplication (no division) | Full |
| Zicond | Conditional Operations | Full |
| Zihintpause | Pause Hint Instruction | Full |
| Sub-extension | Description | Status |
|---|---|---|
| Zca | Integer Compressed Instructions | Full |
| Zcb | Additional Compressed Instructions | Full |
| Sub-extension | Description | Status |
|---|---|---|
| Zalrcs | Load-Reserved/Store-Conditional Instructions | Full |
| Zammo | Atomic Memory Operations | Full |
Atomic instructions are passed through the pipeline and handled by the data cach
| Sub-extension | Description | Status |
|---|---|---|
| Zba | Address Generation | Full |
| Zbb | Basic Bit-Manipulation | Full |
| Zbs | Single-Bit Operations | Full |
| Zbc | Carry-less Multiplication | Full |
| Extension | Description | Status |
|---|---|---|
| Zicsr | Control Status Registers | Full |
| Zicntr | Base Counters and Timers | Full |
| Zihpm | Hardware Performance Monitors | Only mhpmcounter3-9 |
SARV currently implements the three standard RISC-V privilege modes:
| Mode | Description | Status |
|---|---|---|
| M-mode | Machine mode | Supported |
| S-mode | Supervisor mode | Supported |
| U-mode | User mode | Supported |
Supervisor trap and interrupt handling is supported through the corresponding supervisor CSRs and delegation mechanisms.
| Interrupt | Description | Status |
|---|---|---|
| MEI | Machine External Interrupt | Supported |
| MTI | Machine Timer Interrupt | Supported |
| MSI | Machine Software Interrupt | Supported |
| Interrupt | Description | Status |
|---|---|---|
| SEI | Supervisor External Interrupt | Supported |
| STI | Supervisor Timer Interrupt | Supported |
| SSI | Supervisor Software Interrupt | Supported |
- Supervisor interrupt delegation is handled through
mideleg. - SARV includes support for the Supervisor-level Timer Compare extension (Sstc).
| Feature | Description | Status |
|---|---|---|
| WFI | Wait for Interrupt — halts core until IRQ | Supported |
| Clock throttling | Runtime control of switching activity | Supported |
| Metric | Value |
|---|---|
| CoreMark | 1508.755307 |
| Frequency | 500 MHz (simulated) |
| CoreMark/MHz | 3.017510614 |
| Simulation | Gate-level, ideal memory |
| Flags | -march=rv32ib_zicond_zmmul_zicsr_zca -mabi=ilp32 -Ofast |
Measured in gate-level simulation without cache/memory latency. Provides architectural comparison point.
The design under test uses:
- A Branch Target Buffer (BTB) with 8 entries (
BRANCH_PREDICTION_ENTRY_INDEX_BITS = 3). - A Return Address Stack (RAS) with 2 entries (
RETURN_ADDRESS_PREDICTION_ENTRY_INDEX_BITS = 1). ENABLE_CARRY_LESS_MULTIPLIER = 1.ENABLE_EMBEDDED_BASE = 0.
| Test Suite | Status |
|---|---|
| CoreMark | Pass |
| unprivilege Custom tests | Pass |
| M/S/U privilege Custom tests | Pass |
| Metric | Value |
|---|---|
| Total Area | 38,354.008000 µm² |
| Cell Count | 26,670 |
| KGE | 48.06 kGE |
| Sequential Area | 16,199.4 µm² (42.24%) |
| Synthesis Tool | Yosys |
| Post-synthesis estimated Fmax | 550 MHz |
The figure below shows the top level organization of the SARV core. Detailed down to wire and module documentation are available in the docs/ directory:
complete schematic
The SARV core has been tested using:
- Simulator: QuestaSim 2024.1
vlog rtl/*.vvsim work.tb_top
run -allNote: Before running the simulation, update the instruction memory initialization file (
memory.txt) to point to your desired program image and current path.
SARV is licensed under the CERN Open Hardware Licence Version 2 – Strongly Reciprocal (CERN-OHL-S-2.0).
You are free to use, modify, and manufacture hardware based on this project, provided you comply with the terms of the CERN-OHL-S v2.
See the LICENSE file for details.