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SENT USB Converter Integration Test

Comprehensive pytest-based integration test for bidirectional SENT communication between two SENTToUSB devices.

Overview

The test suite verifies:

  • ✓ Both TX and RX devices are present and responsive
  • ✓ Devices can enter RX/TX modes
  • ✓ SENT frames transmit and receive correctly
  • ✓ Multiple tick times work: 3µs, 6µs, 9µs, 12µs
  • ✓ Frame sequences are handled correctly
  • ✓ Tick time settings persist across multiple frames

Setup

Hardware Requirements

  • 2x SENTToUSB devices connected to USB
  • Default configuration: COM15 (TX) and COM20 (RX)
    • Customize by modifying TX_PORT and RX_PORT in the test class

Software Requirements

  1. Install pytest and pyserial:

    pip install -r test_requirements.txt

    Or manually:

    pip install pytest>=7.0.0 pyserial>=3.5

Running Tests

Run all tests with verbose output:

pytest test_sent_integration.py -v -s

Run only tick-time parametrized tests:

pytest test_sent_integration.py::TestSENTIntegration::test_tx_rx_with_tick_time -v -s

Run a specific tick time (e.g., 3µs):

pytest test_sent_integration.py::TestSENTIntegration::test_tx_rx_with_tick_time[3.0] -v -s

Run tests without capturing output (real-time logging):

pytest test_sent_integration.py -v -s --capture=no

Generate test report:

pytest test_sent_integration.py -v --tb=short --html=report.html

Test Cases

Basic Connectivity Tests

Test Purpose
test_devices_present_and_responsive Verify both devices enumerate and respond to version query
test_can_enter_rx_mode Verify RX device accepts RX mode command
test_can_enter_tx_mode Verify TX device accepts TX mode command

Communication Tests

Test Purpose
test_tx_rx_with_tick_time[X] Send/receive frames at tick time X µs (parametrized for 3, 6, 9, 12)
test_tx_rx_with_tick_and_frame_size[X-5] Combined parametrized test: tick time X µs with DLC=5 (firmware accepts DLC=5 only on 0x520)
test_multiple_frames_sequence Verify 10-frame sequence transmits and receives in order
test_rx_only_without_tx Verify RX device can listen without errors on quiet channel
test_tick_time_persistence_across_frames[X] Verify tick time setting persists for 5 consecutive frames
test_all_frame_sizes_with_default_tick Sanity-check default-tick TX (DLC=5 baseline)

Note: the firmware bridge rejects 0x520 TX frames with DLC < 5 (see handle_tx_can_frame in Core/Src/sent_bridge.c). Tests therefore only exercise DLC=5. The number of data nibbles encoded inside the frame is set via the 0x001 config frame, not via DLC.

Test Frames

SLCAN Command Format

t<ID><DLC><data>\r   Standard frame (11-bit CAN ID)
T<ID><DLC><data>\r   Extended frame (29-bit CAN ID)

Control Commands (CAN ID 0x600)

t600101\r       Start RX mode      (DLC=1, data=[0x01])
t600102\r       Start TX mode      (DLC=1, data=[0x02])
t600103\r       Stop               (DLC=1, data=[0x03])
t600305LLHH\r   Set TX tick        (DLC=3, data=[0x05, LL, HH])
                LLHH = little-endian 16-bit value in 0.1 µs units
                e.g. 3.0 µs → tick_x10 = 30 = 0x001E → t6003051E00

TX Data Frames (CAN ID 0x520)

t52050100123400\r
  ID=0x520, DLC=5, data=[0x01, 0x00, 0x12, 0x34, 0x00]
  data[0]   = status nibble (low 4 bits): 0x1
  data[1..3]= 6 nibbles MSB-first: [0x0, 0x0, 0x1, 0x2, 0x3, 0x4]
  data[4]   = unused for 6-nibble config (default), but DLC must still be 5

RX Decoded Frames (CAN ID 0x510, default)

t5103AABBCC\r
  Fast channel output: 3 bytes (6 nibbles)
  DLC=3 for fast-channel only
  DLC=7 when slow-channel message completes

Customizing Port Configuration

Edit the test class at the top of test_sent_integration.py:

class TestSENTIntegration:
    TX_PORT = "COM15"      # Change to your TX device port
    RX_PORT = "COM20"      # Change to your RX device port
    TICK_TIMES = [3.0, 6.0, 9.0, 12.0]  # Modify tested tick times

Expected Output

The suite collects 18 test cases:

Group Count
Connectivity (test_devices_present_and_responsive, test_can_enter_rx_mode, test_can_enter_tx_mode) 3
test_tx_rx_with_tick_time (4 tick × 1) 4
test_tx_rx_with_tick_and_frame_size (4 tick × DLC=5) 4
test_multiple_frames_sequence 1
test_rx_only_without_tx 1
test_tick_time_persistence_across_frames (4 tick × 1) 4
test_all_frame_sizes_with_default_tick 1
Total 18

A full pass typically takes 60–90 s; each tick-parametrized case waits several frame periods to drain the RX side before asserting.

Debugging

Enable detailed logging:

Add to test file or run with environment variable:

pytest test_sent_integration.py -v -s --log-cli-level=DEBUG

Check device connectivity before running tests:

python -c "import serial; s = serial.Serial('COM15', 115200, timeout=1); s.write(b'V\r'); print(s.read(50).decode())"

Verify devices are present:

# On Windows PowerShell:
Get-PnpDevice -Class Ports | Where-Object {$_.Status -eq 'OK'}

# Or use the device manager GUI

Troubleshooting

"Failed to connect to COM15/COM20"

  • Check devices are plugged in
  • Verify correct COM port numbers (use Device Manager)
  • Update port numbers in test class

"No frames received"

  • Verify firmware is built and flashed to both devices
  • Check USB cable connections
  • Try with loopback test: connect TX and RX outputs together
  • Review hardware timing fixes in SENT_timing_fixes.md

"DLC mismatch" or frame parse errors

  • Check SLCAN command format is correct
  • Verify data length matches DLC field
  • Review SLCAN protocol in main README.md

Test passes locally but fails in CI/CD

  • Serial port enumeration may differ in CI environment
  • Use environment variables to override port numbers
  • Consider adding parametrization for multiple port configurations

Performance Notes

  • Each tick-time test takes ~5-10 seconds (including device initialization, frame transmission, and RX timeout)
  • Full test suite (~13 tests) completes in 45-60 seconds
  • Frame latency: typically 10-100 ms depending on USB CDC overhead
  • RX timeout set to 2.0s per frame batch; adjust if seeing false negatives

Related Files

License

Test suite follows the same license as the SENTToUSB project.