Pros of Ibex

• More extensive documentation and user guides
• Broader range of supported extensions (e.g., RV32E, RV32M)
• Active development with frequent updates and contributions

Cons of Ibex

• Slightly higher power consumption
• Less optimized for specific applications compared to CV32E40P
• May require more area on chip due to additional features

Code Comparison

CV32E40P:

module cv32e40p_core
  import cv32e40p_pkg::*;
#(
  parameter PULP_XPULP          = 0,
  parameter PULP_CLUSTER        = 0,
  parameter FPU                 = 0,
  parameter PULP_ZFINX          = 0,
  parameter NUM_MHPMCOUNTERS    = 1
)

Ibex:

module ibex_core #(
  parameter bit          PMPEnable         = 1'b0,
  parameter int unsigned PMPGranularity    = 0,
  parameter int unsigned PMPNumRegions     = 4,
  parameter int unsigned MHPMCounterNum    = 0,
  parameter int unsigned MHPMCounterWidth  = 40,
  parameter bit          RV32E             = 1'b0,
  parameter bit          RV32M             = 1'b1,
  parameter bit          RV32B             = 1'b0,
  parameter bit          BranchTargetALU   = 1'b0,

Both repositories offer open-source RISC-V cores, but they cater to slightly different use cases. CV32E40P focuses on embedded applications with PULP extensions, while Ibex provides a more general-purpose core with broader RISC-V extension support. The code comparison shows differences in parameterization and feature sets between the two cores.

Pros of riscv-boom

• Higher performance with out-of-order execution and superscalar design
• More advanced features like branch prediction and speculative execution
• Scalable architecture supporting different configurations (small, medium, large)

Cons of riscv-boom

• Higher complexity and resource usage
• Potentially longer development and verification cycles
• May be overkill for simpler embedded applications

Code comparison

cv32e40p (simple in-order pipeline):

always_comb begin
  instr_valid = id_ready_i & (~halt_if_i) & id_in_ready_o;
  pc_set_o    = 1'b0;
  pc_mux_o    = PC_BOOT;
  exc_pc_mux_o = EXC_PC_IRQ;
end

riscv-boom (out-of-order execution):

class Scheduler(
  num_entries: Int,
  num_wakeup_ports: Int,
  issue_width: Int,
  plWidth: Int,
  numLlPorts: Int,
  numWbPorts: Int,
  numPregsMSB: Int
) extends BoomModule

The code snippets highlight the difference in complexity between the two designs. cv32e40p shows a simple combinational logic block for instruction fetching, while riscv-boom demonstrates a more complex scheduler class for managing out-of-order execution.

Pros of rocket-chip

• More comprehensive and feature-rich RISC-V implementation
• Supports multiple core configurations and customization options
• Extensive ecosystem and tooling support

Cons of rocket-chip

• Higher complexity and steeper learning curve
• Larger codebase, potentially more challenging to modify or debug
• May require more resources for synthesis and implementation

Code Comparison

cv32e40p (RISC-V core implementation):

module cv32e40p_core
  import cv32e40p_pkg::*;
#(
  parameter PULP_XPULP        = 0,
  parameter PULP_CLUSTER      = 0,
  parameter FPU               = 0,
  parameter PULP_ZFINX        = 0,
  parameter NUM_MHPMCOUNTERS  = 1
)
(
  // Clock and Reset
  input  logic        clk_i,
  input  logic        rst_ni,

rocket-chip (Rocket core generator):

class Rocket(
  traceParams: TraceParams = TraceParams(),
  val dcache: Option[DCacheParams] = Some(DCacheParams()),
  val icache: Option[ICacheParams] = Some(ICacheParams()),
  val mmu: Option[MMUParams] = Some(MMUParams()),
  val core: RocketCoreParams = RocketCoreParams()
)(implicit p: Parameters) extends CoreModule()(p)
    with HasRocketCoreParameters
    with HasL1CacheParameters {

Pros of VexRiscv

• Written in SpinalHDL, allowing for more flexible and modular design
• Highly configurable with various optional features and extensions
• Better performance in some benchmarks due to optimized implementation

Cons of VexRiscv

• Less widespread industry adoption compared to cv32e40p
• Documentation may be less comprehensive for some users
• Potentially steeper learning curve due to SpinalHDL

Code Comparison

cv32e40p (SystemVerilog):

module cv32e40p_core
  import cv32e40p_pkg::*;
#(
  parameter PULP_XPULP        = 0,
  parameter PULP_CLUSTER      = 0,
  parameter FPU               = 0,
  parameter PULP_ZFINX        = 0,
  parameter NUM_MHPMCOUNTERS  = 1
)

VexRiscv (SpinalHDL):

case class VexRiscvConfig(
  plugins : Seq[Plugin[VexRiscv]],
  prediction : BranchPrediction = NONE,
  bypassExecute0 : Boolean = false,
  bypassExecute1 : Boolean = false,
  bypassWriteBack : Boolean = false,
  bypassWriteBackBuffer : Boolean = false
)

Pros of cva6

• Supports 64-bit RISC-V architecture, offering more advanced computing capabilities
• Implements out-of-order execution, potentially improving performance
• Includes a more complex pipeline, suitable for high-performance applications

Cons of cva6

• Higher complexity and resource requirements compared to cv32e40p
• Potentially longer development and verification cycles
• May consume more power, making it less suitable for low-power applications

Code Comparison

cv32e40p:

module cv32e40p_core
  import cv32e40p_pkg::*;
#(
  parameter PULP_XPULP          = 0,
  parameter PULP_CLUSTER        = 0,
  parameter FPU                 = 0,
  parameter PULP_ZFINX          = 0,
  parameter NUM_MHPMCOUNTERS    = 1
)

cva6:

module ariane import ariane_pkg::*; #(
  parameter int unsigned ADDR_WIDTH = 64,
  parameter int unsigned DATA_WIDTH = 64,
  parameter bit          RV32       = 0,
  parameter int unsigned HART_ID    = 0
) (

The code snippets show the module declarations for both cores, highlighting the differences in architecture and configuration options.

Pros of freedom

• More comprehensive SoC design, including CPU cores, peripherals, and system integration
• Supports multiple RISC-V core configurations (E31, S51, U54)
• Includes additional tools and documentation for FPGA implementation

Cons of freedom

• Larger and more complex codebase, potentially harder to understand and modify
• Less focused on a single core implementation, which may be overkill for some projects
• May require more resources to synthesize and implement on FPGAs

Code comparison

cv32e40p (RV32IMC implementation):

module cv32e40p_core
  import cv32e40p_pkg::*;
#(
  parameter PULP_XPULP        = 0,
  parameter PULP_CLUSTER      = 0,
  parameter FPU               = 0,
  parameter PULP_ZFINX        = 0,
  parameter NUM_MHPMCOUNTERS  = 1
)

freedom (RV64GC implementation):

module Rocket
(
  input clock,
  input reset,
  input hartid,
  output [63:0] io_imem_req_bits_addr,
  input io_imem_resp_valid,
  input [63:0] io_imem_resp_bits_data,

The cv32e40p focuses on a 32-bit RISC-V core, while freedom's Rocket core is a 64-bit implementation with more advanced features. The freedom project provides a broader ecosystem for RISC-V development, while cv32e40p offers a more targeted solution for embedded applications.