README.adoc

RISC-V Compliance Tests

Table of Contents

• 1. Introduction
  • 1.1. About
  • 1.2. Purpose of compliance tests
  • 1.3. Intended audience
  • 1.4. Future work
  • 1.5. Feedback and how to contribute
  • 1.6. Contributors
  • 1.7. Document history
• 2. Overall structure
  • 2.1. The compliance test
  • 2.2. The Test Virtual Machine
  • 2.3. The target environment
  • 2.4. The processor configuration (device configuration)
  • 2.5. The test signature
  • 2.6. The test reference signature
  • 2.7. The test suites
  • 2.8. The test framework
• 3. Developing new tests
  • 3.1. Structure
  • 3.2. Process
• 4. Test framework
• 5. Setting the target environment
  • 5.1. Imperas riscvOVPsim compliance simulator
  • 5.2. Codasip ISA simulator
  • 5.3. GNU CGEN ISS
  • 5.4. Berkeley Spike ISA simulator
  • 5.5. SiFive Freedom Unleashed 540 board (tbd)
  • 5.6. Verilator Verilog RI5CY RTL processor
  • 5.7. Adding a new Target
• 6. Configuring the target device
• Appendix A: One ISA Test
• Appendix B: Repository structure
• Appendix C: Creative Commons Attribution 4.0 International License
  • C.1. Using Creative Commons Public Licenses
  • C.2. Creative Commons Attribution 4.0 International Public License
  • Supplementary

1. Introduction

1.1. About

This document describes the RISC-V Compliance Testing framework which is used to test a RISC-V device’s compliance to the different RISC-V specifications.

• It explains the required structure of a test, the framework around the tests, the running of individual tests, and the suites of tests.

• It includes, as reference, details of the first suite of tests for the RV32I and their reference signatures.

• It explains how to set up different targets to run the tests.

• It is an expansion of the work carried out by Codasip in the second half of 2017.

This document is made freely available under a Creative Commons Attribution 4.0 International Public License.

1.2. Purpose of compliance tests

The goal of compliance tests is to check whether the processor under development meets the open RISC-V standards or not. It is considered as non-functional testing meaning that it doesn’t substitute for design verification. This can be interpreted as testing to check all important aspects of the specification but without focusing on details, for example, on all possible values of instruction operands or all combinations of possible registers.

The result that compliance tests provide to the user is an assurance that the specification has been interpreted correctly and the design under test (DUT) can be declared as RISC-V compliant.

1.3. Intended audience

This document is intended for design and verification engineers who wish to develop new compliance tests and also those who wish check if their implementation (simulation models, HDL models, etc.) of a RISC-V processor is compliant to the RISC-V specifications.

1.4. Future work

This is a work in progress. A number of areas need resolving before the work is complete, and are recorded here so they do not get forgotten.

Consider whether compliance_test.h is needed

It’s not clear if this belongs in target directories, or if it is needed at all.

Generalize Makefile configuration

At present each platform requires editing of the makefile, and many areas are not even fully parameterized. Again we wish to explore a wider range of platforms before deciding what needs parameterization. For now COMPILE_TARGET allows a choice between GCC and LLVM. More generally, we know that with tools like autotools and cmake this is a well understood problem to solve.

Free up all registers for compliance testing

At present some platforms have macros which use some registers in set up and verification, thus excluding them from compliance testing. We believe careful structuring of the macros will mean this problem can be avoided in the future, thus avoiding any registers being excluded from compliance testing.

1.5. Feedback and how to contribute

Comments on this document should be made through the RISC-V Compliance Task Group mailing list. Proposed changes may be submitted as git pull requests.

You are encouraged to contribute to this repository by submitting pull requests and by commenting on pull requests submitted by other people as described in the README.md file in the top level directory.

Note	Don’t forget to add your own name to the list of contributors in the document.

1.5.1. AsciiDoc

This is a structured text format used by this document. Simple usage should be fairly self evident.

• Comprehensive information on the format is on the AsciiDoc website.

• Comprehensive information on the tooling on the AsciiDoctor website.

• You may find this cheat sheet helpful.

1.5.2. Installing tools

To generate the documentation as HTML you need asciidoctor and to generate as PDF you need asciidoctor-pdf.

• These are the installation instructions for asciidoctor.

• These are the installation instructions for asciidoctor-pdf.

To spell check you need aspell installed.

1.5.3. Building the documentation

To build HTML:

make html

To build PDF:

make pdf

To build both:

make

To check the spelling (excludes any listing or code phrases):

make spell

Any custom words for spell checking should be added to custom.wordlist.

1.6. Contributors

This document has been created by the following people (in alphabetical order of surname).

Jeremy Bennett, Mary Bennett, Simon Davidmann, Radek Hajek, Lee Moore, Milan Nostersky, Marcela Zachariasova.

1.7. Document history

Revision	Date	Author	Modification
1.10 Draft	20 June 2018	Simon Davidmann, Lee Moore	Cleaned up description of updated framework and inclusion of riscvOVPsim.
1.9 Draft	12 June 2018	Jeremy Bennett	Update Future work section to take account of Codasip changes. Remove diagrammatic directory structure.
1.8 Draft	12 June 2018	Jeremy Bennett	Add Future work section.
1.7 Draft	12 June 2018	Jeremy Bennett	Add CC license as an appendix.
1.6 Draft	10 June 2018	Jeremy Bennett	Tidy up areas that are flawed in HTML version.
1.5 Draft	8 June 2018	Jeremy Bennett	General tidy up.
1.4 Draft	8 June 2018	Jeremy Bennett	Added license preamble.
1.3 Draft	5 June 2018	Simon Davidmann	Updated to reflect directory structure and trace macros.
1.2 Draft	3 June 2018	Jeremy Bennett	Converted to AsciiDoc, cleaned up and restructured.
1.1 Draft	1 June 2018	Simon Davidmann Lee Moore	Revised format and expand to describe framework, usage of many tests groups, and different Targets
1.0	24 December 2017	Radek Hajek Milan Nostersky Marcela Zachariasova	First version of the document.

2. Overall structure

2.1. The compliance test

At the heart of the testing infrastructure is the detailed compliance test. This is the RISC-V assembler code that is executed on the processor and that provides results in a defined memory area (the signature). The test should only use the minimum of instructions and only those absolutely necessary. It should only use instructions and registers from the ISA instruction set on which it is targeted.

2.2. The Test Virtual Machine

The test runs in the context of a Test Virtual Machine (TVM) as defined and available at https://github.com/riscv/riscv-tests. There will be a different TVM for each instruction subset and each profile.

2.3. The target environment

A specific target will need to be chosen and setup to run the Test. This can be an Instruction Set Simulator (ISS), full system simulator (emulator), HDL simulator, FPGA prototype, or a board/chip, etc. The test runs in the context of a TVM and is set up to run on the specific target. The target environment controls the loading of the test plus TVM onto the target, configures the device if needed, controls the execution, and then extracts the signature.

2.4. The processor configuration (device configuration)

The RISC-V specification allows many optional instructions, registers, and other features. Many targets have a fixed selection of these optional items which cannot be changed. For example, a chip is fixed in the mask. A simulator on the other hand may implement all known options and will need to be constrained to have only the required options available. There will need to be processor configuration for those target devices which need to be constrained to only reflect the features of the device being compliance tested. This is essential when writing compliance tests to ensure that only available options are used in the tests.

2.5. The test signature

The test signature is defined as reference data written into memory during the execution of the test. It should record values and results of the operation of the Test.

2.6. The test reference signature

The test reference signature is the test signature saved from an execution run of the RISC‑V golden model. This is currently from a RISC-V ISS, but the intention is that the RISC-V Formal Model from the RISCV.org Formal Working Group will be used when it is complete, functional, and available.

2.7. The test suites

Tests are grouped into different functional test suites targeting the different subsets of the full RISC-V specifications. There will be ISA and privilege suites.

Currently there is one test suite: the RV32I (developed by Codasip).

Test suites will be developed in this priority order:

• RV32I

• RV64I

• RV32IM

• RV64IM

• RV32IC

• RV64IC

• RV32IA

• RV64IA

• RV32IF

• RV64IF

• RV32ID

• RV64ID

• RV32E

• RV32EC

• RV32EA

• RV32EF

• RV32ED

This order is subject to ratification by the Compliance Task Group

2.8. The test framework

This works at several levels. At the lowest level it runs a test with a TVM on a specific configured target device and compares the test’s output test signature against the test reference signature and reports if there is any difference. A difference indicates that the target has failed that specific compliance test.

The test framework allows different test suites to be run depending on the capabilities of the target

The test framework collates the results of all the Tests that comprise a Test Suite and reports the overall results.

3. Developing new tests

3.1. Structure

• Clone directory structure of an existing test suite alongside the RV32I tree.

• This must include test and reference signature directories (src and references).

• Check the target environment setup files.

• Check the processor configuration files.

3.2. Process

This description assumes the use of a configurable simulator with good trace and debug capabilities.

• Work on one test at a time.

• Ensure that the processor configuration is set appropriately.

• Use the RVTEST macros (defined in compliance_io.h) to make it easy to see the details of a Test’s execution. There are macros for assertions (RVTEST_IO_ASSERT_GPR_EQ) and tracing (RVTEST_IO_WRITE_STR) which are empty on targets that can not implement them.

• Assuming you are developing the test on a simulator, use the simulator’s tracing capabilities, especially a register change mode to single step your test examining all changing registers etc. to ensure your test is stimulating what is intending.

• Make sure that the signature you generate at the end of the run shows adequate internal test state such that any checks do report as fails if wrong.

• When you are satisfied that the test does what is intended and that the test signature is correct, copy this into a test reference signature (in the references directory).

For a test suite to be complete it needs to have tests that exercise the full functionality of what it is intended to test. There are tools available to measure instruction and other resource coverage. These should be used to ensure that 100% of the intended instructions have been tested.

4. Test framework

For running compliance tests, the Test Virtual Machine (TVM) “p” available at https://github.com/riscv/riscv-tests is utilized.

In addition to using the basic functionality of the TVM, the script for running compliance tests runs the test on the target and then performs comparison of the target’s generated test signature to the manually reviewed test reference signature.

See the chapter below for selecting and setting up the target (simulator, or hardware, etc.).

If using a target that requires the processor to be configured, see the chapter below on processor configuration.

You will also need to have a suitable compiler tool chain (GCC or LLVM) installed in your environment and available on your path.

Tests are run by commands in the top level Makefile which has targets for simulate and verify

RISCV_TARGET ?= riscvOVPsim
RISCV_DEVICE ?= rv32i
RISCV_PREFIX ?= riscv64-unknown-elf-

simulate:
        make RISCV_TARGET=$(RISCV_TARGET) \
             RISCV_DEVICE=$(RISCV_DEVICE) \
             RISCV_PREFIX=$(RISCV_PREFIX) \
             run -C $(SUITEDIR)

verify:
    riscv-test-env/verify.sh

5. Setting the target environment

The target environment needs setting up to allow the compliance tests to be run on the target. This can be used while developing compliance test suites or it can be used with new targets to see if they correctly execute the compliance test suites and are compliant!

This chapter provides information on the currently available targets and includes a short tutorial on how to add a new target.

5.1. Imperas riscvOVPsim compliance simulator

For tracing the test the following macros are defined in riscv-target/riscvOVPsim/compliance_io.h:

RVTEST_IO_INIT
RVTEST_IO_WRITE_STR(_STR)
RVTEST_IO_ASSERT_GPR_EQ(_R, _I)

An example of a test that uses the tracing macros is riscv-test-suite/rv32i/ISA/src/I-IO.S.

To configure the simulator for different target devices there needs to be a Makefile fragment in the device directory.

The Makefile fragment for RV32I is in riscv-target/riscvOVPsim/device/rv32i

In the top level Makefile there needs to be a selection for the target and device:

RISCV_TARGET?=riscvOVPsim
RISCV_DEVICE?=rv32i

The path to the RUN_TARGET is defined within the riscv-target Makefile.include.

5.2. Codasip ISA simulator

tbd

5.3. GNU CGEN ISS

5.3.1. Within GDB

tbd

5.3.2. Via GDB Remote Serial Protocol

tbd

5.4. Berkeley Spike ISA simulator

For spike the file riscv-target/spike/compliance_io.h has the trace macros defined as empty. The Makefile fragment in riscv-target/spike/device/rv32i has the spike run command for the RV32I device.

5.5. SiFive Freedom Unleashed 540 board (tbd)

tbd

5.6. Verilator Verilog RI5CY RTL processor

5.6.1. With GDB Server

tbd

5.6.2. With testbench monitor

tbd

5.7. Adding a new Target

In this section, a short tutorial how to add a user target in the TVM is provided.

If you do not want to use the TVM at all, it is recommended to just take the tests and references and incorporate them into your testing environment. The only requirement needed in this case is that there must be an option to dump the results from the target in the test environment so as the comparison to test reference signature is possible.

The following steps demonstrate an example in which a target was replaced by Codasip ISA simulator. In a similar way, any RISC-V ISA simulator or any RTL simulation model of the RISC-V processor can be connected.

• Redefine macros in ISA/src/compliance_test.h and binary_coding/src/compliance_test.h.

  For example, to support Codasip ISA simulator as Target, it was necessary to redefine RV_COMPLIANCE_HALT macro, RV_COMPLIANCE_DATA_BEGIN macro and RV_COMPLIANCE_DATA_END macro in ISA/compliance_test.h in the following way:

  #define RV_COMPLIANCE_HALT
          add     x31, x0, 1
          sw      x31, codasip_syscall, t0

• This means that on the address defined by codasip_syscall, the 1 value is stored and this is interpreted as HALT for the Codasip ISA simulator.

  #define RV_COMPLIANCE_DATA_BEGIN
          .align  4;
          .global codasip_signature_start;
  codasip_signature_start:

  #define RV_COMPLIANCE_DATA_END
          .align  4;
          .global codasip_signature_end;
  codasip_signature_end:

• The Codasip ISA simulator dumps data from the addresses bounded by labels codasip_signature_start and codasip_signature_end to stdout. The dumped data represent the results of the tests.

• Modify Makefiles in ISA/Makefile and binary_coding/Makefile. It is important to change tools that are evaluated and parameters that are passed to the tools.

  For example, to support the Codasip ISA simulator as the device under test (DUT), it was necessary to change RISCV_SIM from spike to codix_berkelium-ia-isimulator –r and parameters for running the simulator from +signature=$(work_dir)/$<_signature.output to –info 5 plus handle redirection to a file by 1>$(work_dir)/$<_signature.output.

6. Configuring the target device

This section is for how to specify which optional parts are being used

Note	This is primarily for simulators.

In the directory riscv-target/*/device there are directories that have Makefile fragments that configure the simulator to simulate only those parts of the RISC-V specification that is required for the specific target device being tested.

For example for the riscvOVPsim to be configured to be a RV32I

RUN_TARGET= \
        riscvOVPsim.exe --variant RV32I --program $(work_dir_isa)/$< \
            --signaturedump \
            --override riscvOVPsim/cpu/sigdump/SignatureFile=$(work_dir_isa)/$(*)_signature.output \
            --override riscvOVPsim/cpu/sigdump/ResultReg=3 \
            --override riscvOVPsim/cpu/simulateexceptions=T \
            --logfile $(work_dir_isa)/$@

Appendix A: One ISA Test

For a detailed description of one ISA test please have a look at the example: I-IO.S.

This includes use of all the logging and assertion macros and shows how a test is split into sections.

Appendix B: Repository structure

The top level directory contains a README.md file giving an overview of the project, top level Makefile, ChangeLog, the verify.sh script and complete license files for the Creative Commons and BSD licenses used by the task group. There are then four top level directories.

doc

All the documentation for the project, written using AsciiDoc.

riscv-target

Contains a further subdirectory for each target, within which are placed the compliance_io.h header for that target and a device directory for all the devices of that target.

riscv-test-env

This contains headers common to all environments, and then a directory for each TVM variant, with link.ld linker script and riscv_test.h header.

riscv-test-suite

This contains a subdirectory for each instruction set or instruction set extension. Within each subdirectory the source code and reference output for each test are in the ISA directory.

riscv-ovpsim

This contains a copy of the Imperas OVP riscvOVPsim simulator for use in compliance testing. It includes a subdirectory of examples with pre-compiled .elf files and has binaries of the simulator for Linux64 and Windows64. This is referenced by the makefiles for developing and running the compliance suites. riscvOVPsim can run all the tracing and assertion macros used in the tests.

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