HMAC DV document

Goals

DV
- Verify all HMAC 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

Design features

For detailed information on HMAC design features, please see the HMAC design specification.

Testbench architecture

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

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

Common DV utility components

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

Global types & methods

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

parameter uint32 HMAC_MSG_FIFO_DEPTH       = 16;
parameter uint32 HMAC_MSG_FIFO_DEPTH_BYTES = HMAC_MSG_FIFO_DEPTH * 4;
parameter uint32 HMAC_MSG_FIFO_SIZE        = 2048;

TL_agent

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

UVM RAL Model

The HMAC 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:

Reference models

To check the correctness of the output for SHA256 and HMAC, the testbench uses the C reference model. Messages and keys generated by constrained random test sequences are passed on to the reference model. Then the hmac scoreboard will compare the reference model’s expected digest data with the DUT output.

Stimulus strategy

Test sequences

All test sequences reside in hw/ip/hmac/dv/env/seq_lib. The hmac_base_vseq virtual sequence is extended from cip_base_vseq and serves as a starting point. All test sequences are extended from hmac_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:

hmac_init : initialize hmac settings including configurations and interrupt enables
csr_rd_digest : read digest values from the CSR registers
wr_key : write key values into the CSR registers
wr_msg : write messages into the hmac_msg_fifo
compare_digest: compare the read digest result with the expected values

Standard test vectors

Besides constrained random test sequences, hmac test sequences also includes standard SHA256 and HMAC test vectors from NIST and IETF. The standard test vectors provide messages, keys (for HMAC only), and expected results. The expected results are used to cross verify both the DUT and DPI-C model outputs.

Functional coverage

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

cfg_cg: Covers configuration registers in HMAC
intr_cg: Covers interrupt registers in HMAC
status_cg: Covers status registers in HMAC
msg_len_cg: Covers streamed-in message length in HMAC

Self-checking strategy

Scoreboard

The hmac_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 address channel
tl_d_chan_fifo: tl data channel

Hmac scoreboard monitors all hmac valid CSR registers, hmac msg_fifo (addr: ‘h800 to ‘hfff), and interrupt pins.

For a write transaction, during the address channel, CSR values are updated in RAL. Msg_fifo values are updated to an internal msg queue. Once the data finishes streaming, hmac scoreboard will input the msg queue to the C model and calculate the expected output, then update the corresponding RAL registers.

For a read transaction, during the address channel, for status related CSRs (such as fifo_full, fifo_empty, etc), hmac will predict its value according to the cycle accurate model. During the data channel, hmac scoreboard will compare the read data with expected data in RAL.

Scoreboard cycle accurate checking model

Hmac scoreboard contains a cycle accurate checking to model the hmac internal message fifo. It has two pointers(hmac_wr_cnt and hmac_wr_cnt) to simulate the read and write of the hmac internal message fifo. These two pointers are updated at the negedge of the clock cycle to avoid glitch. Read pointer is incremented one clock cycle after the write pointer (except if HMAC is enabled, then read will first wait 80 clock cycles for the key padding). Hmac fifo full is asserted when hmac_wr_cnt - hmac_wr_cnt == 16. Hmac fifo depth is checked against the difference between hmac_wr_cnt and hmac_rd_cnt.

Assertions

TLUL assertions: The tb/hmac_bind.sv binds the tlul_assert assertions to hmac 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/hmac/dv/hmac_sim_cfg.hjson -i hmac_smoke

Testplan

Testpoints

Stage	Name	Tests	Description
V1	smoke	hmac_smoke	HMAC smoke test performs a few round of HMAC or SHA256-ONLY transactions with the prodecures below: Set configuration register to randomly enable SHA256, hmac, endian_swap, and digest_swap Set interrupt enable register to randomly enable fifo_full, hmac_done, and err_code interupts Randomly read previous digest result Write key Trigger HMAC hash_start Write HMAC message fifo with message length between 0 and 64 bytes check status and interrupt Trigger HMAC hash_process After hmac_done interrupt, read and check digest data
V1	csr_hw_reset	hmac_csr_hw_reset	Verify the reset values as indicated in the RAL specification. Write all CSRs with a random value. Apply reset to the DUT as well as the RAL model. Read each CSR and compare it against the reset value. it is mandatory to replicate this test for each reset that affects all or a subset of the CSRs. It is mandatory to run this test for all available interfaces the CSRs are accessible from. Shuffle the list of CSRs first to remove the effect of ordering.
V1	csr_rw	hmac_csr_rw	Verify accessibility of CSRs as indicated in the RAL specification. Loop through each CSR to write it with a random value. Read the CSR back and check for correctness while adhering to its access policies. It is mandatory to run this test for all available interfaces the CSRs are accessible from. Shuffle the list of CSRs first to remove the effect of ordering.
V1	csr_bit_bash	hmac_csr_bit_bash	Verify no aliasing within individual bits of a CSR. Walk a 1 through each CSR by flipping 1 bit at a time. Read the CSR back and check for correctness while adhering to its access policies. This verify that writing a specific bit within the CSR did not affect any of the other bits. It is mandatory to run this test for all available interfaces the CSRs are accessible from. Shuffle the list of CSRs first to remove the effect of ordering.
V1	csr_aliasing	hmac_csr_aliasing	Verify no aliasing within the CSR address space. Loop through each CSR to write it with a random value Shuffle and read ALL CSRs back. All CSRs except for the one that was written in this iteration should read back the previous value. The CSR that was written in this iteration is checked for correctness while adhering to its access policies. It is mandatory to run this test for all available interfaces the CSRs are accessible from. Shuffle the list of CSRs first to remove the effect of ordering.
V1	csr_mem_rw_with_rand_reset	hmac_csr_mem_rw_with_rand_reset	Verify random reset during CSR/memory access. Run csr_rw sequence to randomly access CSRs If memory exists, run mem_partial_access in parallel with csr_rw Randomly issue reset and then use hw_reset sequence to check all CSRs are reset to default value It is mandatory to run this test for all available interfaces the CSRs are accessible from.
V1	regwen_csr_and_corresponding_lockable_csr	hmac_csr_rw hmac_csr_aliasing	Verify regwen CSR and its corresponding lockable CSRs. Randomly access all CSRs Test when regwen CSR is set, its corresponding lockable CSRs become read-only registers Note: If regwen CSR is HW read-only, this feature can be fully tested by common CSR tests - csr_rw and csr_aliasing. If regwen CSR is HW updated, a separate test should be created to test it. This is only applicable if the block contains regwen and locakable CSRs.
V2	long_msg	hmac_long_msg	Long_msg test is based on the smoke test. The message length is between 0 and 10,000 bytes.
V2	back_pressure	hmac_back_pressure	Back_pressure test is based on the long_msg test. The test disabled all the protocol delays to make sure to have high chance of hitting the FIFO_FULL status.
V2	test_vectors	hmac_test_sha_vectors hmac_test_hmac_vectors	From NIST and IETF websites, this test intends to use HMAC and SHA test vectors to check if the reference model predicts correct data, and check if DUT returns correct data.
V2	burst_wr	hmac_burst_wr	Burst_wr test is based on the long_msg test. The test intends to test burst write a pre-defined size of message without any status or interrupt checking.
V2	datapath_stress	hmac_datapath_stress	Datapath_stress test is based on the long_msg test. It enabled HMAC and message length is set to N*64+1 in order to stress the datapath.
V2	error	hmac_error	This error case runs sequences that will cause interrupt bit hmac_err to set. This sequence includes: Write msg_fifo or set hash_start when sha is disabled Update secret key when hash is in process Set hash_start when hash is active Write msg before hash_start is set
V2	wipe_secret	hmac_wipe_secret	This test issues wipe_secret on hmac process datapath. Based on the smoke sequence, this sequence increases the message length, and randomly issues wipe_secret in one of the following scenarios: Before entering HMAC secret keys. This scenario represents wiping secrets when HMAC is idle. Before issuing HMAC start command. This scenario represents wiping secrets when HMAC entered secret keys. Before issuing HMAC process command. This scenario represents wiping secrets when HMAC is streaming in message data. Before HMAC finishes hashing process. This scenario represents wiping secrets when HMAC is hashing messages and keys. Checks: The scoreboard will check if digest data are corrupted.
V2	stress_all	hmac_stress_all	Stress_all test is a random mix of all the test above except csr tests.
V2	alert_test	hmac_alert_test	Verify common `alert_test` CSR that allows SW to mock-inject alert requests. Enable a random set of alert requests by writing random value to alert_test CSR. Check each `alert_tx.alert_p` pin to verify that only the requested alerts are triggered. During alert_handshakes, write `alert_test` CSR again to verify that: If `alert_test` writes to current ongoing alert handshake, the `alert_test` request will be ignored. If `alert_test` writes to current idle alert handshake, a new alert_handshake should be triggered. Wait for the alert handshakes to finish and verify `alert_tx.alert_p` pins all sets back to 0. Repeat the above steps a bunch of times.
V2	intr_test	hmac_intr_test	Verify common intr_test CSRs that allows SW to mock-inject interrupts. Enable a random set of interrupts by writing random value(s) to intr_enable CSR(s). Randomly "turn on" interrupts by writing random value(s) to intr_test CSR(s). Read all intr_state CSR(s) back to verify that it reflects the same value as what was written to the corresponding intr_test CSR. Check the cfg.intr_vif pins to verify that only the interrupts that were enabled and turned on are set. Clear a random set of interrupts by writing a randomly value to intr_state CSR(s). Repeat the above steps a bunch of times.
V2	tl_d_oob_addr_access	hmac_tl_errors	Access out of bounds address and verify correctness of response / behavior
V2	tl_d_illegal_access	hmac_tl_errors	Drive unsupported requests via TL interface and verify correctness of response / behavior. Below error cases are tested bases on the [TLUL spec]({{< relref "hw/ip/tlul/doc/_index.md#explicit-error-cases" >}}) TL-UL protocol error cases invalid opcode some mask bits not set when opcode is `PutFullData` mask does not match the transfer size, e.g. `a_address = 0x00`, `a_size = 0`, `a_mask = 'b0010` mask and address misaligned, e.g. `a_address = 0x01`, `a_mask = 'b0001` address and size aren't aligned, e.g. `a_address = 0x01`, `a_size != 0` size is greater than 2 OpenTitan defined error cases access unmapped address, expect `d_error = 1` when `devmode_i == 1` write a CSR with unaligned address, e.g. `a_address[1:0] != 0` write a CSR less than its width, e.g. when CSR is 2 bytes wide, only write 1 byte write a memory with `a_mask != '1` when it doesn't support partial accesses read a WO (write-only) memory write a RO (read-only) memory write with `instr_type = True`
V2	tl_d_outstanding_access	hmac_csr_hw_reset hmac_csr_rw hmac_csr_aliasing hmac_same_csr_outstanding	Drive back-to-back requests without waiting for response to ensure there is one transaction outstanding within the TL device. Also, verify one outstanding when back- to-back accesses are made to the same address.
V2	tl_d_partial_access	hmac_csr_hw_reset hmac_csr_rw hmac_csr_aliasing hmac_same_csr_outstanding	Access CSR with one or more bytes of data. For read, expect to return all word value of the CSR. For write, enabling bytes should cover all CSR valid fields.
V2S	tl_intg_err	hmac_tl_intg_err hmac_sec_cm	Verify that the data integrity check violation generates an alert. Randomly inject errors on the control, data, or the ECC bits during CSR accesses. Verify that triggers the correct fatal alert. Inject a fault at the onehot check in `u_reg.u_prim_reg_we_check` and verify the corresponding fatal alert occurs
V2S	sec_cm_bus_integrity		Verify the countermeasure(s) BUS.INTEGRITY.
V3	write_config_and_secret_key_during_msg_wr	hmac_smoke	Change config registers and secret keys during msg write, make sure access is blocked.
V3	stress_all_with_rand_reset	hmac_stress_all_with_rand_reset	This test runs 3 parallel threads - stress_all, tl_errors and random reset. After reset is asserted, the test will read and check all valid CSR registers.

Covergroups

Name	Description
cfg_cg	Covers the cfg configurations below and their cross: hmac_en endian_swap digest_swap
err_code_cg	Covers the error scenarios below: No error. Push message when sha is disabled. Hash starts when sha is disabled. Update secret key when hash is in progress. Issue hash start again when hash in progress. Push message when hmac is idle.
msg_len_cg	Covers the length of the streamed in message.
regwen_val_when_new_value_written_cg	Cover each lockable reg field with these 2 cases: When regwen = 1, a different value is written to the lockable CSR field, and a read occurs after that. When regwen = 0, a different value is written to the lockable CSR field, and a read occurs after that. This is only applicable if the block contains regwen and locakable CSRs.
status_cg	Covers the status bits below and cross them with different configurations above: fifo_empty fifo_full fifo_depth
tl_errors_cg	Cover the following error cases on TL-UL bus: TL-UL protocol error cases. OpenTitan defined error cases, refer to testpoint `tl_d_illegal_access`.
tl_intg_err_cg	Cover all kinds of integrity errors (command, data or both) and cover number of error bits on each integrity check. Cover the kinds of integrity errors with byte enabled write on memory if applicable: Some memories store the integrity values. When there is a subword write, design re-calculate the integrity with full word data and update integrity in the memory. This coverage ensures that memory byte write has been issued and the related design logic has been verfied.

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