In FS6500 SBC, what happens if MCU fails to service watchdog in the 1st 256ms refresh period?

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In FS6500 SBC, what happens if MCU fails to service watchdog in the 1st 256ms refresh period?

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Contributor III

As to switch from INIT_FS mode to Normal_WD mode in SBC, 1 good watchdog refresh is essential by MCU; but if the MCU fails to do so in 256msec, then RSTB, FS0B & FS1B(after Tdelay time) are asserted low. So at this time, SBC remains in INIT_FS mode only & the window of 256msec expires, then what happens next? Does it move into Deep Failsafe state? or SBC restarts?

Thanks in advance.

5 Replies

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NXP Employee
NXP Employee

Hi,  Vaibhav

If FS65 is in init_FS mode and MCU does not refresh WD in 256ms, then RSTB will be triggered and FS65 will open one new 256ms Window(Init_FS mode) to allow MCU to refresh WD again, meanwhile Fault error counter will be increased by 1. 

If MCU cannot refresh WD always, once Fault error counter is increased to 6(default) ,FS65 will go into deep fail safe mode(if deep fail safe mode is enabled). 

Br

Dennis 

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Contributor III

Hi Dennis,

Thanks for the response.

If deep FS mode is disabled, then it goes to LPOFF-sleep, right?

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NXP Employee
NXP Employee

Hi, Vaibhav

No, If FS mode is disabled.  FS65 cannot go to LP_OFF-sleep mode even fault error counter reach maximum value. 

Br

Dennis

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Contributor III

Hi Dennis,

Thanks for the clarification.

So, if deep FS is disabled, MSM remains in normal mode & regulators are kept on. Only condition to go into LPOFF-sleep is associated with the 8 sec timer for RSTB pin(if deep FS is disabled).

You wrote,"If FS65 is in init_FS mode and MCU does not refresh WD in 256ms, then RSTB will be triggered "=> So the RSTB will go low & then high again? as it was already high in INIT_FS phase.

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NXP Employee
NXP Employee

Hi, Vaibhav

Pls. refer to below answer:

So, if deep FS is disabled, MSM remains in normal mode & regulators are kept on. Only condition to go into LPOFF-sleep is associated with the 8 sec timer for RSTB pin(if deep FS is disabled).

Dennis->Yes, if deep FS is disabled, one condition to go into LPOFF-Sleep is  RSTB keep low for 8s.

 

You wrote,"If FS65 is in init_FS mode and MCU does not refresh WD in 256ms, then RSTB will be triggered "=> So the RSTB will go low & then high again? as it was already high in INIT_FS phase.

Dennis->Yes, RSTB of FS65 will have a 10ms low pulse if its WD is not refreshed in init_FS(256ms).

Br

Dennis