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README.md

BrqRV EB1 RISC-V Core 1.0 from MERL

This repository contains the brqrv eb1 Core design RTL. Brqrv Eb1 Is A Machine-Mode (M-Mode) Only, 32-Bit Cpu Small Core Which Supports Risc-V’s Integer (I), Compressed Instruction (C), Multiplication And Division (M), And Instruction-Fetch Fence, And Csr Extensions. The Core Contains A 4-Stage, Scalar, In-Order Pipeline

Block Diagram

Directory Structure

├── configs                 # Configurations Dir
│   └── snapshots           # Where generated configuration files are created
├── design                  # Design root dir
│   ├── dbg                 #   Debugger
│   ├── dec                 #   Decode, Registers and Exceptions
│   ├── dmi                 #   DMI block
│   ├── exu                 #   EXU (ALU/MUL/DIV)
│   ├── ifu                 #   Fetch & Branch Prediction
│   ├── include             
│   ├── lib
│   └── lsu                 #   Load/Store
├── docs
├── tools                   # Scripts/Makefiles
└── testbench               # (Very) simple testbench
    ├── asm                 #   Example assembly files
    ├── hex                 #   Canned demo hex files
    └── tests               #   Example tests

Dependencies

  • Verilator (4.102 or later) must be installed on the system if running with verilator
  • If adding/removing instructions, espresso must be installed (used by tools/coredecode)
  • RISCV tool chain (based on gcc version 8.3 or higher) must be installed so that it can be used to prepare RISCV binaries to run.

Quickstart guide

  1. Clone the repository
  2. Setup RV_ROOT to point to the path in your local filesystem
  3. Determine your configuration {optional}
  4. Run make with tools/Makefile

Configurations

BrqRV can be configured by running the $RV_ROOT/configs/brqrv.config script:

% $RV_ROOT/configs/brqrv.config -h for detailed help options

For example to build with a DCCM of size 64 Kb:

% $RV_ROOT/configs/brqrv.config -dccm_size=64

This will update the default snapshot in $RV_ROOT/configs/snapshots/default/ with parameters for a 64K DCCM.

Add -snapshot=dccm64, for example, if you wish to name your build snapshot dccm64 and refer to it during the build.

This script derives the following consistent set of include files :

$RV_ROOT/configs/snapshots/default
├── common_defines.vh                       # `defines for testbench or design
├── defines.h                               # #defines for C/assembly headers
├── eb1_param.vh                            # Design parameters
├── eb1_pdef.vh                             # Parameter structure
├── pd_defines.vh                           # `defines for physical design
├── perl_configs.pl                         # Perl %configs hash for scripting
├── pic_map_auto.h                          # PIC memory map based on configure size
└── whisper.json                            # JSON file for brqrv-iss
└── link.ld                                 # default linker control file

Building a model

while in a work directory:

  1. Set the RV_ROOT environment variable to the root of the brqrv directory structure. Example for bash shell:
    export RV_ROOT=/path/to/brqrv
    Example for csh or its derivatives:
    setenv RV_ROOT /path/to/brqrv

  2. Create your specific configuration

    (Skip if default is sufficient)
    (Name your snapshot to distinguish it from the default. Without an explicit name, it will update/override the default snapshot) For example if mybuild is the name for the snapshot:

    set BUILD_PATH environment variable:

    setenv BUILD_PATH snapshots/mybuild

    $RV_ROOT/configs/brqrv.config [configuration options..] -snapshot=mybuild

    Snapshots are placed in $BUILD_PATH directory

  3. Running a simple Hello World program (verilator)

    make -f $RV_ROOT/tools/Makefile

This command will build a verilator model of brqrv eb1 with AXI bus, and execute a short sequence of instructions that writes out “HELLO WORLD” to the bus.

The simulation produces output on the screen like:


VerilatorTB: Start of sim ---------------------------------- Hello World from brqrv eb1 @WDC !! ---------------------------------- TEST_PASSED Finished : minstret = 437, mcycle = 922 See "exec.log" for execution trace with register updates..

The simulation generates following files:

console.log contains what the cpu writes to the console address of 0xd0580000.
exec.log shows instruction trace with GPR updates.
trace_port.csv contains a log of the trace port.
When debug=1 is provided, a vcd file sim.vcd is created and can be browsed by gtkwave or similar waveform viewers.

You can re-execute simulation using:
make -f $RV_ROOT/tools/Makefile verilator

The simulation run/build command has following generic form:

make -f $RV_ROOT/tools/Makefile [<simulator>] [debug=1] [snapshot=mybuild] [target=<target>] [TEST=<test>] [TEST_DIR=<path_to_test_dir>]

where:

<simulator> -  can be 'verilator' (by default) 'irun' - Cadence xrun, 'vcs' - Synopsys VCS, 'vlog' Mentor Questa
               'riviera'- Aldec Riviera-PRO. if not provided, 'make' cleans work directory, builds verilator executable and runs a test.
debug=1     -  allows VCD generation for verilator and VCS and SHM waves for irun option.
<target>    -  predefined CPU configurations 'default' ( by default), 'default_ahb', 'typical_pd', 'high_perf' 
TEST        -  allows to run a C (<test>.c) or assembly (<test>.s) test, hello_world is run by default 
TEST_DIR    -  alternative to test source directory testbench/asm or testbench/tests
<snapshot>  -  run and build executable model of custom CPU configuration, remember to provide 'snapshot' argument 
               for runs on custom configurations.
CONF_PARAMS -  allows to provide -set options to brqrv.conf script to alter predefined eb1 targets parameters

Example:

make -f $RV_ROOT/tools/Makefile verilator TEST=cmark

will build and simulate testbench/asm/cmark.c program with verilator

If you want to compile a test only, you can run:

make -f $RV_ROOT/tools/Makefile program.hex TEST=<test> [TEST_DIR=/path/to/dir]