L9679P datasheet(184/272 Pages) STMICROELECTRONICS

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Watchdog timers

L9679P

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DocID029275 Rev 1

Following the description of the WD2 states and signals (most of them available through SPI

registers)

Table 14. WD2 states and signals

State / Signal

Description

WD2 INIT

Default state entered from startup or after a SSM reset (if not in WD2 STOP

state).

WD2 OVERRIDE

Special state used to disable WD2 watchdog functionality.

WD2 INITSEED

State entered when the correct default key is received in INIT state. Here

the timer starts to count waiting for the real first key.

WD2 RUN

Normal run-time state where WD2 service is required.

WD2 TEST

A special state used to test the watchdog function. Normally, this state will

only be checked once per power cycle by the software, but there is no

inherent restriction in the watchdog logic preventing periodic testing. This

state allows testing of the watchdog without affecting WD2 error (no reset is

generated, WD2_LOCKOUT stay low). Only WD2_WDR latch could be set

to 1, in this way μC is able to verify the functionality of the watchdog.

WD2 QUAL

A state used to qualify a number of WD2_ERROR occurrences before

action is taken. The intent is to use this state to permit a retry strategy to

account for software jitter.

WD2 LOCK

A state entered after the allowed retries have been exhausted. This is

where action is taken due to WD2 service failure.

WD2 STOPPING

This is a timed-duration state that is automatically exited after 1ms

WD2 STOP

A state used to prevent continual recovery of WD2 errors using the

WD2_KEY key mechanism to restart watchdog service.

WD2 RESET

State entered when a WD2_ERROR occurs after having been qualified in

the WD2_QUAL state (when all retries are exhausted), or when testing the

WD2. This is a timed-duration state that is automatically exited after 1ms.

WSM_RESET

Watchdog State Machine reset – used to force a transition to the WD2 INIT

state and reset all signals to their inactive states

WD2_RETRY

Counter that tracks the number of retry attempts. It is incremented each

time the logic detects a WD2 error while qualifying the error.

WD2_WDR

Watchdog Reset – latched signal that is activated whenever a watchdog

error is qualified. For WD2, this occurs when WD2 service not received

after all retry attempts have previously failed. This signal is SPI-readable.

WD2_TM

Test Mode – a signal that indicates that WD2 is being tested. This signal is

SPI-readable.

WD2_LOCKOUT

A latched signal that is activated on startup, or whenever a WD2 error is

fully qualified (all retry attempts have failed). Recovery is still possible after

this is set going into WD2 RUN state. This signal drives the

WD2_LOCKOUT output pin. This signal is SPI-readable.

SPI_WD2_TEST

SPI command used to enter WD2_TEST state or to enter WD2 OVERRIDE

state from INIT.

TMR2

Timer to count the maximum time limit to receive the correct key

SPI_WD2_RECOVER SPI command used to clear retry counter

WD2_ERR_CNT

Counter that tracks the number of WD2 error occurred

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