2416003_en-US

[#1]

FS85 stuck in INIT_FS forever when OTP_CFG_ASIL.WD_DIS = 1 — is this expected?

Hi,

We're bringing up a board with the FS85 (fail-safe SBC) and the fail-safe state machine never leaves INIT_FS (FS_STATES.FSM_STATE stays at 6 / INIT_FS indefinitely, even though the MCU sends a continuous watchdog refresh at the configured window period).

Per the datasheet (Rev 9, §14.3, p.18): "The first good watchdog refresh closes the INIT_FS." On our part, OTP_CFG_ASIL.WD_DIS = 1 (watchdog monitoring disabled by OTP).

Supporting register reads while stuck (all consistent with the watchdog evaluation logic simply never running):

• FS_I_WD_CFG.WD_ERR_CNT = 0, WD_RFR_CNT = 0 (never move)
• FS_DIAG_SAFETY.BAD_WD_DATA = 0, BAD_WD_TIMING = 0 (never latch)
• FS_STATES.REG_CORRUPT = 0, OTP_CORRUPT = 0 (ruling out an INIT_FS register/register_NOT mismatch)

Question: Is it expected/documented that WD_DIS = 1 structurally prevents ever leaving INIT_FS (since the "good watchdog refresh" event that closes INIT_FS can never be generated when the WD is OTP-disabled)? Or is there an alternate documented path to close INIT_FS and reach NORMAL_FS when the watchdog is disabled by OTP?

Datasheet section 14.1/14.3 states VALID_WD = 0 "when the WD is disabled by OTP", but doesn't explicitly state the consequence on the INIT_FS -> WAIT_ABIST2 transition. Any clarification, or a pointer to the relevant application note, would be appreciated.

Thanks, Sophie

FS85&FS84Re: FS85 stuck in INIT_FS forever when OTP_CFG_ASIL.WD_DIS = 1 — is this expected?

Hello sobo

Good day!

During my research, I found information on a similar case, and I am reviewing it with a colleague who was responsible for its review; however, given the nature of the case, you will need to open a ticket on our official website so that we can share information more freely and securely.

Thanks for your understanding.

Have a great day and best of luck.