Level Defines - Technical Documentation

Contents

1. Overview
2. Feature Flags
3. Multiplier Implementations
4. Trace and Log Controls
5. Simulation Controls
6. Makefile Integration
7. Usage Examples

---

Overview

Purpose

The level_defines.svh file provides compile-time configuration for the Level RISC-V core. This header provides central definitions for feature flags, multiplier selection, and trace controls.

File Location

rtl/include/level_defines.svh

Include Method

`include "level_defines.svh"

---

Feature Flags

Multiplier Selection

Only one multiplier implementation may be active at a time:

//------------------------------------------------------------------------------
// MULTIPLIER IMPLEMENTATION SELECTION
// Enable only ONE of the following multiplier implementations
//------------------------------------------------------------------------------

// Single-cycle Wallace tree multiplier (default - best performance)
`define FEAT_WALLACE_SINGLE

// Multi-cycle Wallace tree multiplier (area optimized)
//`define FEAT_WALLACE_MULTI

// DSP block multiplier (FPGA optimized)
//`define FEAT_DSP_MUL

Multiplier Comparison

Implementation	Latency	Throughput	Area	Use case
WALLACE_SINGLE	1 cycle	1/cycle	High	Performance
WALLACE_MULTI	N cycle	1/N cycle	Low	Area opt.
DSP_MUL	1-3 cycle	1/cycle	DSP	FPGA

---

Multiplier Implementations

Wallace Single (Default)

`define FEAT_WALLACE_SINGLE

// Usage
`ifdef FEAT_WALLACE_SINGLE
    // Single-cycle 32x32 Wallace tree
    wallace_mul_single u_mul (
        .i_a    (operand_a),
        .i_b    (operand_b),
        .o_prod (product)
    );
`endif

Features: - 32x32 multiply in one cycle - 64-bit result - High area usage - Long critical path

Wallace Multi

//`define FEAT_WALLACE_MULTI

// Usage
`ifdef FEAT_WALLACE_MULTI
    // Multi-cycle radix-4 Booth multiplier
    wallace_mul_multi u_mul (
        .clk_i      (clk),
        .rst_ni     (rst_n),
        .i_start    (mul_start),
        .i_a        (operand_a),
        .i_b        (operand_b),
        .o_prod     (product),
        .o_done     (mul_done)
    );
`endif

Features: - Multi-cycle multiply (4-16 cycles) - Low area usage - Requires pipeline stalls

DSP Multiplier

//`define FEAT_DSP_MUL

// Usage
`ifdef FEAT_DSP_MUL
    // FPGA DSP48 block multiplier
    dsp_mul u_mul (
        .clk_i  (clk),
        .i_a    (operand_a),
        .i_b    (operand_b),
        .o_prod (product)
    );
`endif

Features: - Uses FPGA DSP block - 1-3 cycle latency (pipeline) - Low logic usage - Vendor-specific

---

Trace and Log Controls

Trace Flags

These flags are normally commented out and enabled via the makefile:

//------------------------------------------------------------------------------
// TRACE AND LOGGING CONTROLS
// These are typically enabled via makefile +define+ flags
//------------------------------------------------------------------------------

// `define COMMIT_TRACER     // Carry trace info in pipeline registers
// `define KONATA_TRACER     // Konata pipeline visualizer support
// `define LOG_COMMIT        // Spike-compatible commit trace
// `define LOG_RAM           // RAM initialization messages
// `define LOG_UART          // UART TX file logging
// `define LOG_BP            // Branch predictor statistics
// `define LOG_BP_VERBOSE    // Per-branch verbose logging

Flag Descriptions

Flag	Description	Output
COMMIT_TRACER	Carries trace info in pipeline registers	-
KONATA_TRACER	Konata pipeline visualizer support	pipeline.log
LOG_COMMIT	Spike-comparable commit trace	commit.log
LOG_RAM	RAM load messages	Console
LOG_UART	UART TX output logged to file	uart.log
LOG_BP	Branch predictor statistics	Console
LOG_BP_VERBOSE	Verbose log per branch	Console

---

Simulation Controls

Simulation Flags

//------------------------------------------------------------------------------
// SIMULATION CONTROLS
// Enabled via makefile for simulation modes
//------------------------------------------------------------------------------

// `define SIM_FAST           // Disable all logging for speed
// `define SIM_UART_MONITOR   // UART monitoring + auto-stop
// `define SIM_COVERAGE       // Enable coverage collection

SIM_FAST Mode

`ifdef SIM_FAST
    // All logs disabled
    // Maximum simulation speed
`else
    // Normal debug modunda
    `ifdef LOG_COMMIT
        // Commit trace aktif
    `endif
`endif

SIM_UART_MONITOR

`ifdef SIM_UART_MONITOR
    // Monitor UART output
    // Stop simulation when PASS or FAIL is seen
    // Detect benchmark results
`endif

---

Makefile Integration

Passing Verilator Defines

# Trace kontrolleri
LOG_COMMIT ?= 0
LOG_PIPELINE ?= 0
LOG_RAM ?= 0
LOG_UART ?= 0
LOG_BP ?= 0
LOG_BP_VERBOSE ?= 0
KONATA_TRACER ?= 0

# Pass defines to Verilator
VFLAGS_DEFINES :=
ifeq ($(LOG_COMMIT),1)
    VFLAGS_DEFINES += +define+LOG_COMMIT
endif
ifeq ($(KONATA_TRACER),1)
    VFLAGS_DEFINES += +define+KONATA_TRACER +define+COMMIT_TRACER
endif
# ... other flags

Usage Examples

# Sadece commit trace
make run T=rv32ui-p-add LOG_COMMIT=1

# Pipeline visualizer
make run T=rv32ui-p-add KONATA_TRACER=1 LOG_PIPELINE=1

# Branch predictor stats
make run_coremark LOG_BP=1 SIM_UART_MONITOR=1

# Fast simulation
make run T=coremark SIM_FAST=1

# All logs
make run T=test LOG_COMMIT=1 LOG_RAM=1 LOG_UART=1 LOG_BP=1

---

Usage Examples

Conditional Compilation

module example
  import level_param::*;
(
    input logic clk_i,
    // ...
);

`ifdef FEAT_WALLACE_SINGLE
    // Single-cycle multiplier
    assign mul_done = 1'b1;  // Always ready
`elsif FEAT_WALLACE_MULTI
    // Multi-cycle multiplier
    logic mul_busy;
    // ...
`endif

`ifdef LOG_COMMIT
    always_ff @(posedge clk_i) begin
        if (commit_valid) begin
            $display("core   0: 0x%08x (0x%08x) x%0d 0x%08x",
                     commit_pc, commit_instr, commit_rd, commit_data);
        end
    end
`endif

endmodule

Guard Pattern

`ifndef LEVEL_DEFINES_SVH
`define LEVEL_DEFINES_SVH

// Define contents

`endif // LEVEL_DEFINES_SVH

Cross-Module Dependency

// KONATA_TRACER aktifse, COMMIT_TRACER da gerekli
`ifdef KONATA_TRACER
    `ifndef COMMIT_TRACER
        `define COMMIT_TRACER
    `endif
`endif

---

Flag Dependencies

Relationship Diagram

┌─────────────────────────────────────────────────────────────────────────────────┐
│                          FLAG DEPENDENCIES                                       │
├─────────────────────────────────────────────────────────────────────────────────┤
│                                                                                  │
│   KONATA_TRACER ──────────────────────► COMMIT_TRACER                           │
│        │                                     │                                   │
│        │                                     ▼                                   │
│        │                              Pipeline registers                         │
│        │                              carry trace info                           │
│        │                                                                         │
│        ▼                                                                         │
│   LOG_PIPELINE ─────────────────────► pipeline.log output                       │
│                                                                                  │
│                                                                                  │
│   LOG_COMMIT ───────────────────────► commit.log output                         │
│        │                                     │                                   │
│        │                                     ▼                                   │
│        │                              Spike comparison                           │
│        │                                                                         │
│                                                                                  │
│   SIM_FAST ─────────────────────────► Disables all LOG_*                        │
│                                                                                  │
│                                                                                  │
│   LOG_BP_VERBOSE ───────────────────► LOG_BP                                    │
│                                                                                  │
└─────────────────────────────────────────────────────────────────────────────────┘

Implicit Dependencies

Flag	Requires
KONATA_TRACER	COMMIT_TRACER (auto-enabled)
LOG_BP_VERBOSE	LOG_BP (implied)
SIM_FAST	Disables all LOG_* flags

---

Best Practices

1. Multiplier Selection

// Only one multiplier implementation should be active
`define FEAT_WALLACE_SINGLE
//`define FEAT_WALLACE_MULTI  // Comment out
//`define FEAT_DSP_MUL        // Comment out

2. Trace Logs

// Normalde comment halinde
// Enable via Makefile
//`define LOG_COMMIT

// Makefile:
// make run T=test LOG_COMMIT=1

3. Debug vs Release

# Debug build (default)
make run T=test MODE=debug

# Release build (minimal logging)
make run T=coremark MODE=release SIM_FAST=1

# Test mode (assertions enabled)
make isa MODE=test

---

Summary

The level_defines.svh file:

1. Feature Selection: Multiplier implementasyonu
2. Trace Control: Commit, pipeline, UART logging
3. Simulation Modes: Fast, coverage, UART monitor
4. Makefile Integration: Runtime define passing
5. Conditional Compilation: ifdef/endif pattern

This header file supports different configurations of the Level RISC-V core.