SPI_HOST DV Document

Goals

  • DV
    • Verify all SPI_HOST IP features by running dynamic simulations with a SV/UVM based testbench
    • Develop and run tests that exercise all testpoints in 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 features

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

Testbench architecture

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

Block diagram

Block diagram

Top level testbench

Top level testbench is located at hw/ip/spi_host/dv/tb/tb.sv. It instantiates the SPI_HOST DUT module hw/ip/spi_host/rtl/spi_host.sv. In addition, it instantiates the following interfaces, connects them to the DUT 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:

Compile-time configurations

[list compile time configurations, if any and what are they used for]

  // sets the number of spi devices
  parameter int NumCS = 1;

Currently there verification only covers NumCS = 1 since this is the configuration that will be used in tapeout. Endianess implemented and verified is only Little Endian with ByteOrder set to 1

Global types & methods

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

  // types
  typedef enum int {
    SpiHostError     = 0,
    SpiHostEvent     = 1,
    NumSpiHostIntr   = 2
  } spi_host_intr_e;

  typedef enum int {
    TxFifo   = 0,
    RxFifo   = 1,
    AllFifos = 2
  } spi_host_fifo_e;

  typedef enum {
    Command,
    Address,
    Dummy,
    Data
  } spi_segment_type_e;

  // spi config
  typedef struct {
    // configopts register fields
    rand bit        cpol[SPI_HOST_NUM_CS];
    rand bit        cpha[SPI_HOST_NUM_CS];
    rand bit        fullcyc[SPI_HOST_NUM_CS];
    rand bit [3:0]  csnlead[SPI_HOST_NUM_CS];
    rand bit [3:0]  csntrail[SPI_HOST_NUM_CS];
    rand bit [3:0]  csnidle[SPI_HOST_NUM_CS];
    rand bit [15:0] clkdiv[SPI_HOST_NUM_CS];
  } spi_host_configopts_t;

  typedef struct {
    // csid register
    rand bit [31:0] csid;
    // control register fields
    rand bit [8:0]  tx_watermark;
    rand bit [6:0]  rx_watermark;
  } spi_host_ctrl_t;

  // spi direction
  typedef enum bit [1:0] {
    None     = 2'b00,
    RxOnly   = 2'b01,
    TxOnly   = 2'b10,
    Bidir    = 2'b11
  } spi_dir_e;

  typedef struct {
    // command register fields
    rand spi_mode_e mode;
    rand spi_dir_e  direction;
    rand bit        csaat;
    rand bit [8:0]  len;
  } spi_host_command_t;

  typedef struct packed {
    bit          status;
    bit          active;
    bit          txfull;
    bit          txempty;
    bit          txstall;
    bit          tx_wm;
    bit          rxfull;
    bit          rxempty;
    bit          rxstall;
    bit          byteorder;
    bit          rsv_0;
    bit          rx_wm;
    bit [19:16]  rsv_1;
    bit [15:8]   rx_qd;
    bit [7:0]    tx_qd;
  } spi_host_status_t;

  typedef struct packed{
    bit csidinval;
    bit cmdinval;
    bit underflow;
    bit overflow;
    bit cmdbusy;
  } spi_host_error_enable_t;

  typedef struct packed{
    bit accessinval;
    bit csidinval;
    bit cmdinval;
    bit underflow;
    bit overflow;
    bit cmdbusy;
  } spi_host_error_status_t;

  typedef struct packed{
    bit idle;
    bit ready;
    bit txwm;
    bit rxwm;
    bit txempty;
    bit rxfull;
  } spi_host_event_enable_t;

  typedef struct{
    bit spi_event;
    bit error;
  } spi_host_intr_state_t;

  typedef struct{
    bit spi_event;
    bit error;
  } spi_host_intr_enable_t;

  typedef struct{
    bit spi_event;
    bit error;
  } spi_host_intr_test_t;

TL_agent

SPI_HOST 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 SPI_HOST device. Transactions will be sampled by the monitor and passed on to the predictor in the scoreboard.

SPI Agent

SPI agent is configured to work in device mode. The Agent will decode the SPI transactions send by the DUT and respond with random data to any read command received. Write data is discarded. The agent sequence could potentially be upgraded to work as a BFM that could store writes for later read back. In the current state the agent recognises 6 commands:

  • ReadStd: 8’b11001100
  • WriteStd: 8’b11111100
  • ReadDual: 8’b00000011
  • WriteDual: 8’b00001100
  • ReadQuad: 8’b00001111
  • WriteQuad: 8’b11110000
  • CmdOnly: 8’b10000001

for V1 only ReadStd, WriteStd and CmdOnly has been implemented.

The agent monitor will capture both the outgoing host transactions where it creates an item for the device sequence and for the scoreboard to check agains the configuration. and the incoming device transactions where it will capture the response items and forward them to another tlm_analysis_port in the host scoreboard.

UVM RAL Model

The SPI_HOST 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/spi_host/dv/env/seq_lib. The spi_host_base_vseq virtual sequence is extended from cip_base_vseq and serves as a starting point. On top of spi_host_base_vseq is spi_host_tx_rx_vseq which form more complex task from the basic tasks in the base vseq. All test sequences are extended from spi_host_tx_rx_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:

  • generate_transaction()

    Generates a SPI transaction of n segments with command, address, dummy and data segements

  • read_rx_fifo()

    Read available data in the RX fifo

  • send_trans_(spi_transaction_item trans)

    Will handle the sequence of writing potential data to the tx fifo and then configuring the DUT to transmit it in correct order.

Functional coverage

To ensure high quality constrained random stimulus, it is necessary to develop a functional coverage model. The list of functional coverpoints can be found under covergroups in the testplan

Self-checking strategy

Scoreboard

The spi_host_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_UL AGENT

  • tl_a_chan_fifo: tl address channel
  • tl_d_chan_fifo: tl data channel

SPI_AGENT

  • host_data_fifo: outgoing SPI item from the DUT captured by the monitor
  • device_data_fifo: incoming SPI item for the DUT captured by the monitor

When a host programs the DUT to transmit a SPI message. The tl-ul agent monitor will capture these in tl items and forward these to the tl_a_chan_fifo. A predictor will use the tl-ul transactions to generate the expected SPI items. The SPI agent monitor will capture the actual transmitted SPI segments into SPI items and forward them to the host_data_fifo. And the scoreboard will compare the items from the fifo to the expected items created by the predictor to validate the transaction.

The SPI device will generate responses to the SPI commands from the DUT. The SPI agent monitor will capture these into SPI items which are forwarded to the device_data_fifo A predictor will take these and generate the expected tl data response. The host will then read these from the DUT rx fifo. The read transaction is captured and forwarded to the tl_d_chan_fifo When the scoreboard receives an item on the tl_d_chan_fifo it will match the data to the predicted data to validate the transaction. This way both outgoing and incoming transactions are validated independently of each other.

Assertions

  • TLUL assertions: The tb/spi_host_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/spi_host/dv/spi_host_sim_cfg.hjson -i spi_host_smoke

Testplan

Testpoints

Milestone Name Tests Description
V1 smoke spi_host_smoke

SPI_HOST smoke test in which random (rd/wr) transactions are sent to the DUT and received asynchronously with scoreboard checks.

Stimulus:

  • Enable spi_host ip
  • Write data in standard mode - and read it back

Checking:

  • Ensure transactions are transmitted/received correctly
V1 csr_hw_reset spi_host_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 spi_host_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 spi_host_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 spi_host_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 spi_host_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_csrspi_host_csr_rw
spi_host_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.

V1 mem_walk spi_host_mem_walk

Verify accessibility of all memories in the design.

  • Run the standard UVM mem walk sequence on all memories in the RAL model.
  • It is mandatory to run this test from all available interfaces the memories are accessible from.
V1 mem_partial_access spi_host_mem_partial_access

Verify partial-accessibility of all memories in the design.

  • Do partial reads and writes into the memories and verify the outcome for correctness.
  • Also test outstanding access on memories
V2 performance spi_host_performance

Send/receive transactions at max bandwidth

Stimulus:

  • Program the content of timing fields of CONFIGOPTS to the min values
  • Programming TX1_CNT and TXN_CNT to issue read/write back-to-back transactions
  • Read/write rx_fifo/tx_fifo as soon as possible (avoid stalling transactions)

Checking:

  • Ensure transactions are transmitted/received correctly
V2 error_event_intr spi_host_overflow_underflow
spi_host_error_cmd
spi_host_event

This test includes multi tasks which verify error/event interrupt assertion (except TX OVERFLOW error interrupt is verified in separate test)

Stimulus:

  • Program ERROR_ENABLE/EVENT_ENABLE register to enable corresponding error/event interrupt assertion
  • Program transaction with proper constraints to assert error/event interrupts

Checking:

  • Ensure transactions are transmitted/received correctly
  • Ensure the matching between the bit-field values of ERROR_STATUS and ERROR_ENABLE respectively once the error interrupt pin is asserted
  • Ensure the matching between the bit-field values of ERROR_ENABLE once the event interrupt pin is asserted
V2 clock_rate spi_host_speed

Stimulus:

  • select different settings for:
  • CONFIGOPTS_0.CSNIDLE_0
  • CONFIGOPTS_0.CSNLEAD_0
  • CONFIGOPTS_0.CSNTRAIL_0

Checking:

  • verify that merging of commands work correctly
  • verify that the DUT can handle different sck -> cs_n timings
V2 speed spi_host_speed

Stimulus:

  • randomly select the DUT to run single/dual/quad mode

Checking:

  • verify that all speeds are supported
V2 chip_select_timing spi_host_speed

Stimulus:

  • Randomly select a setting for the 16bit clock divider

Checking:

  • Check that the DUT operates correctly under different SPI clock speeds
V2 sw_reset spi_host_sw_reset

verify software reset behavior

Stimulus:

  • Reset the spi_host randomly after a random number of data shows up on fifos

Checking:

  • Ensure that reads to RXDATA register yield 0s after the rx_fifo is reset
  • Ensure that transactions are dropped in both the scoreboard and spi_agent monitor after the tx_fifo or spi_fsm is reset
V2 passthrough_mode spi_host_passthrough_mode
  • Verify the function of spi_host in passthrough_mode

Stimulus:

  • Enable Passthrough Mode Checking:
  • Ensure Host to Device and Device to Host paths are switched to Passthrough ports
V2 cpol_cpha spi_host_speed

Stimulus:

  • Randomly chip select for different polarity / phase

Checking:

  • Check that the DUT operates correctly under different cs_n settings
V2 full_cycle

Stimulus:

  • randomly select FULLCYC to be set

Checking:

  • Check that the data can be read one full cycle after the data was asserted
V2 duplex spi_host_smoke

Stimulus:

  • in standard mode set the DUT to run full duplex

Checking:

  • verify that the DUT support both half and full duplex in standard mode.
V2 tx_rx_only spi_host_smoke

Stimulus:

  • in standard mode enable tx only and have the env send garbage back
  • in standard mode enable rx only and have the env ignore the incoming data

Checking:

  • verify that the DUT ignores rx line when in tx only mode
  • verify that the DUT does not drain the tx fifo in rx only mode
V2 stress_all spi_host_stress_all

Support vseq (context) switching with random reset in between.

Stimulus:

  • Combine the above sequences in one test to run sequentially except csr sequence and (requires zero_delays)
  • Randomly add reset between each sequence

Checking:

  • Ensure transactions are transmitted/received correctly
  • Ensure reset is handled correctly
V2 stall spi_host_status_stall

Stimulus:

  • Ongoing transaction has stalled due to lack of available space in the RX FIFO and continues when RX fifo is cleared
  • Ongoing transaction has stalled due to lack of data in the TX FIFO and continues when data is provided in TX FIFO

Checking:

  • Ensure Rxstall occurs and recovers
  • Ensure Txstall occurs and recovers
V2 Idlecsbactive spi_host_idlecsbactive

Stimulus:

  • Pause next segment availability and idly wait for next command

Checking:

  • Ensure transactions goes through even with a segment pause and idle wait in the state IdleCsbActive
V2 alert_test spi_host_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 spi_host_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 spi_host_tl_errors

Access out of bounds address and verify correctness of response / behavior

V2 tl_d_illegal_access spi_host_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 spi_host_csr_hw_reset
spi_host_csr_rw
spi_host_csr_aliasing
spi_host_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 spi_host_csr_hw_reset
spi_host_csr_rw
spi_host_csr_aliasing
spi_host_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 spi_host_tl_intg_err
spi_host_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 winbond

Replace SPI agent with the Winbond Flash model

Stimulus:

  • constraint the Sequence to create welformed transactions that the model understands

Checking:

  • Verify the DUT against the WindBond bfm by making the spi agent passive to verify that we comply with the spi targeted for opentitan
V3 stress_all_with_rand_reset spi_host_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
cdc_cg

Collect coverage on the relationship between the core_clk and the spi_sck to verify that both scenarios with both a slow spi_sck, a very fast spi_sck (2x core_clk) and where the two clocks are very close has been tested

command_cg

Collect coverage that different commant settings, important cross:

  • Direction and SPEED
  • CSAAT and SPEED
config_opts_cg

Collect coverage on the config opts register, some important crosses:

  • CPOL and CPHA, check all 4 combinations are tested
  • CSNLEAD, CSNTRAIL and CSNIDLE
control_cg

Collect coverage on the control register to make sure all options are excercised

  • Tx and RX water mark should have a bin for min value, max value and one for everything in between
csid_cg

Collect coverage that different IDs are used.

different_ch_settings_cg
  • Check that multiple end points was running at different speeds concurrently.
  • Collect coverage that multiple SPI endpoints was run with different config opts
duplex_cg

Collect coverage that we verified both duplex and half duplex

error_en_cg

Collect coverage that all possible errors was enabled

error_status_cg

Collect coverage that all possible errors was seen

event_en_cg

Collect coverage that all events was enabled and seen

interrupt_cg
  • check that we see all scenarios that can cause an interrupt and that the interrupts is fired.
  • also check we can clear the interrupt
interrupts_cg

Collect coverage that all types of interrupt was seen

long_commands_cg

Collect coverage to verify that both a read and write command longer than 4 bytes was seen

num_segment_cg
  • Check that the DUT only transmits what is in a command even if more segments are in the TX FIFO
passthrough_cg

Check that the pass through data is transmitted instead of the data in the tx fifo.

  • Cover that passthrough is activated when a normal transaction is in progress.
  • Cover that data on the passthrough interface is ignored while passthroug disabled.
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.

rx_fifo_underflow_cg

Collect coverage to verify that an attempt was made to underflow the RX FIFO by attempting to read from an empty FIFO

segment_speed_cg
  • Check that we test with transactions that uses different speeds i.e first segment in standard mode, followed by segments in dual or quad mode
stall_cg
  • Check that the DUT stalls if a command is configured to transmit data but the tx fifo is empty
  • check that the data is transmitted when written to the TX fifo after a stall
status_cg

Collect coverage on the status register to make sure all scenarios are checked

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.

tx_fifo_overflow_cg

Collect coverage to verify that an attempt was made to overflow the TX FIFO by attempting to write to a full FIFO

unaligned_data_cg

Collect coverage the alignment of writes to the data window to verify that all possible alignments was seen