CSRNG DV document

Goals

• DV
  • Verify all CSRNG IP features by running dynamic simulations with a SV/UVM based testbench
  • Develop and run all tests based on the testplan below towards closing code and functional coverage on the IP and all of its sub-modules
• FPV
  • Verify TileLink device protocol compliance with an SVA based testbench

Current status

• Design & verification stage
• HW development stages
• Simulation results

Design features

For detailed information on CSRNG design features, please see the CSRNG HWIP technical specification.

Testbench architecture

CSRNG testbench has been constructed based on the CIP testbench architecture.

Block diagram

Top level testbench

Top level testbench is located at hw/ip/csrng/dv/tb/tb.sv. It instantiates the CSRNG DUT module hw/ip/csrng/rtl/csrng.sv. In addition, it instantiates the following interfaces, connects them to the DUT and sets their handle into uvm_config_db:

• Clock and reset interface
• TileLink host interface
• CSRNG IOs
• Interrupts (pins_if
• Alerts (pins_if
• Devmode (pins_if

Common DV utility components

The following utilities provide generic helper tasks and functions to perform activities that are common across the project:

• common_ifs
• dv_utils_pkg
• csr_utils_pkg

Global types & methods

All common types and methods defined at the package level can be found in csrng_env_pkg. Some of them in use are:

parameter uint NUM_HW_APPS = 2;

TL_agent

CSRNG testbench instantiates (already handled in CIP base env) tl_agent which provides the ability to drive and independently monitor random traffic via TL host interface into CSRNG device.

Entropy_src_agent

CSRNG testbench instantiates this push_pull_agent which models the ENTROPY_SRC module.

Csrng_agent

CSRNG testbench instantiates this agent which models the EDN module.

UVM RAL Model

The CSRNG RAL model is created with the ralgen FuseSoC generator script automatically when the simulation is at the build stage.

It can be created manually by invoking regtool:

Stimulus strategy

Test sequences

All test sequences reside in hw/ip/csrng/dv/env/seq_lib. The csrng_base_vseq virtual sequence is extended from cip_base_vseq and serves as a starting point. All test sequences are extended from csrng_base_vseq. It provides commonly used handles, variables, functions and tasks that the test sequences can simple use / call. Some of the most commonly used tasks / functions are as follows:

• csrng_init: Initialize the CSRNG module from the randomized environment variables in the config.

Functional coverage

To ensure high quality constrained random stimulus, it is necessary to develop a functional coverage model. The following covergroups have been developed to prove that the test intent has been adequately met:

• common covergroup for interrupts hw/dv/sv/cip_lib/cip_base_env_cov.sv: Cover interrupt value, interrupt enable, intr_test, interrupt pin

Self-checking strategy

Scoreboard

The csrng_scoreboard is primarily used for end to end checking. It creates the following analysis ports to retrieve the data monitored by corresponding interface agents:

• tl_a_chan_fifo, tl_d_chan_fifo: These 2 fifos provide transaction items at the end of Tilelink address channel and data channel respectively
• entropy_src_fifo, genbits_fifo: The entropy_src_fifo provides transaction items from the predictor and the genbits_fifo provide actual post-entropy_src transaction items to compare

Assertions

• TLUL assertions: The tb/csrng_bind.sv binds the tlul_assert assertions to the IP to ensure TileLink interface protocol compliance.
• Unknown checks on DUT outputs: The RTL has assertions to ensure all outputs are initialized to known values after coming out of reset.

Building and running tests

We are using our in-house developed regression tool for building and running our tests and regressions. Please take a look at the link for detailed information on the usage, capabilities, features and known issues. Here's how to run a smoke test:

$ $REPO_TOP/util/dvsim/dvsim.py $REPO_TOP/hw/ip/csrng/dv/csrng_sim_cfg.hjson -i csrng_smoke

Testplan

Testplan