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READY -> Ignition OFF / Sleep Sequence (LVDU, Ready Relay, TeensyBMS)

This document describes what happens when the system is in STATE_READY and the ignition input is turned OFF. It focuses on the ready relay behavior, the separate HV request path, and the dedicated shutdown message that is sent before the LVDU drops the VCU relay on the way to STATE_SLEEP.

Scope:

  • Software paths in LVDU (include/lvdu.h)
  • Ready relay (DigIo::ready_out)
  • HV request (HVCM_to_bms_hv_request)
  • Pre-sleep shutdown message (LVDU_forceVCUsShutdown)
  • TeensyBMS VCU status feedback (src/teensyBMS.cpp)

1) Starting point: STATE_READY

While in STATE_READY:

  • hvManager.SetHVRequest(true) is asserted.
  • Outputs:
    • DigIo::ready_out is ON.
    • DigIo::condition_out is ON.
    • DigIo::vcu_out is ON.
  • HVCM_to_bms_hv_request is set from the HV manager request (subject to load interlocks).

2) Ignition turns OFF

Input path:

  • UpdateInputs() reads ignition_in and stores ignitionOn.
  • UpdateState() sees ignitionOn == false in STATE_READY.

Transition:

  • STATE_READY -> STATE_CONDITIONING

Side effects of the transition:

  • TransitionTo(STATE_CONDITIONING) sets:
    • diagnosePending = true
    • diagnoseTimer = LVDU_DIAGNOSE_DELAY_STEPS (4000 ms)
  • HV request is still ON because STATE_CONDITIONING is an HV-using state.

3) Ready relay behavior after ignition OFF

During STATE_CONDITIONING:

  • DigIo::ready_out is:
    • ON while diagnosePending == true
    • OFF once the diagnose window expires

Diagnosis behavior:

  • For up to LVDU_DIAGNOSE_DELAY_STEPS, the system expects ready_safety_in to remain asserted. If it drops, an error is posted.
  • After the diagnose timer ends and cooldown passes, ready_out must be OFF and ready_safety_in must be OFF; otherwise errors are posted.

4) HV contactor manager (request vs feedback)

hvManager is the single place the LVDU stores the request to keep HV on.

Key points:

  • hvManager.SetHVRequest(true/false) is controlled by the LVDU state machine.
  • hvManager.IsHVActive() is feedback only and reflects BMS contactor state:
    • IsHVActive() is true only if:
      • BMS_DataValid is true, and
      • BMS_CONT_State == 4 (closed)

So after ignition OFF:

  • The request stays ON while in STATE_CONDITIONING.
  • Actual HV feedback depends on the BMS contactor state.

5) What TeensyBMS sends to the BMS every 100 ms

Every 100 ms TeensyBMS::Task100Ms() sends the VCU status frame to the BMS:

  • Byte 0: LVDU_vehicle_state
  • Byte 1: LVDU_forceVCUsShutdown
  • Byte 2: HVCM_to_bms_hv_request
  • Byte 6: rolling counter
  • Byte 7: CRC

Important distinction:

  • LVDU_forceVCUsShutdown is the shutdown messaging bit that warns the BMS and downstream VCUs that the LVDU is about to drop the VCU relay before entering STATE_SLEEP.
  • HVCM_to_bms_hv_request is only the HV request signal. It controls whether the BMS should keep HV active. It is not the shutdown message.

After ignition OFF:

  • STATE_CONDITIONING keeps the HV request ON.
  • Therefore HVCM_to_bms_hv_request remains 1 while conditioning is active, unless the HV-off interlock is explicitly allowing it to go low.

6) When does LVDU request HV OFF?

LVDU only drops the HV request when it transitions to a non-HV state:

  • STATE_STANDBY
  • STATE_SLEEP
  • STATE_ERROR (explicitly requests HV off)

In the READY -> ignition OFF path:

  • READY -> CONDITIONING
  • Then, if thermalTaskCompleted and diagnosis is not pending:
    • CONDITIONING -> STANDBY
  • On entering STANDBY, hvManager.SetHVRequest(false) is executed.

At that point, HVCM_to_bms_hv_request will go low unless HV loads are still active and the HV-off interlock keeps it high.

7) How sleep shutdown messaging now works

Before the LVDU turns off DigIo::vcu_out and enters STATE_SLEEP, the sleep call sites always transition into STATE_FORCE_VCU_SHUTDOWN first.

During STATE_FORCE_VCU_SHUTDOWN:

  • LVDU_forceVCUsShutdown = 1
  • DigIo::vcu_out stays ON
  • DigIo::condition_out is OFF
  • DigIo::ready_out is OFF

When the delay expires:

  • the next 100 ms cycle transitions to STATE_SLEEP
  • LVDU_forceVCUsShutdown returns to 0
  • DigIo::vcu_out is turned OFF

When the configured delay is 0 ms:

  • the system still enters STATE_FORCE_VCU_SHUTDOWN
  • on the following 100 ms cycle it transitions to STATE_SLEEP

This same pre-sleep delay is used for:

  • normal standby -> sleep shutdown
  • error -> sleep shutdown
  • forced low-voltage sleep shutdown

8) Summary sequence (high level)

  1. STATE_READY, ignition ON:

    • ready_out = ON
    • HVCM_to_bms_hv_request = 1

  2. Ignition OFF:

    • STATE_READY -> STATE_CONDITIONING
    • ready_out = ON during diagnose window
    • HVCM_to_bms_hv_request = 1

  3. Diagnosis ends:

    • ready_out = OFF
    • still in STATE_CONDITIONING, HV request remains ON

  4. Conditioning completes:

    • STATE_CONDITIONING -> STATE_STANDBY
    • hvManager.SetHVRequest(false)
    • HVCM_to_bms_hv_request goes low if no HV loads are active

  5. Before any transition from STATE_STANDBY or STATE_ERROR to STATE_SLEEP completes:

    • STATE_FORCE_VCU_SHUTDOWN is entered
    • TeensyBMS sends VCU status with LVDU_forceVCUsShutdown = 1
    • vcu_out stays ON for the configured delay

  6. After the delay expires:

    • STATE_SLEEP is entered
    • vcu_out turns OFF
    • LVDU_forceVCUsShutdown returns to 0

End state: STATE_SLEEP with the VCU relay off, after the shutdown warning was held long enough to be transmitted.

Default setting:

  • LVDU_force_vcu_shutdown_delay = 1000 ms