At91SAM9X35 can't wakeup.

Discussion around AT91RM9200 and SAM9 Series Products.

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Joined: Sat Jul 11, 2015 4:06 am

At91SAM9X35 can't wakeup.

Mon Jul 13, 2015 5:27 am

Hi ;good friends.A
I have a AT91SAM9X35 device .when I power off the main power and keep the VDDBU . it cant't bootup when I power on the main power sometimes ,at the same time the debug port output nothing . At this time, The CPU can run up when I remove the VDDBU.A
Do you have same idea for my case .A
thanks !
Posts: 10
Joined: Mon Aug 20, 2012 7:41 pm

Re: At91SAM9X35 can't wakeup.

Tue Feb 02, 2016 3:00 pm

AT91SAM9X has a power on sequence bug. I mean it requires proper power up sequence wchich is not well documented. Do not keep power on VDDBU. We had the similar problem and we finally switched to additional external RTC IC to keep date.
Posts: 2
Joined: Thu Nov 26, 2015 12:35 pm

Re: At91SAM9X35 can't wakeup.

Tue Feb 02, 2016 7:07 pm


I had similar issues- some times after powering off or if we unscrew the power connector live, the cpu went unresponsive (we too had backup power for VDDBU). And it was virtually impossible to bring back processor unless suply to VDDBU too cycled. This led to the loss of RTC data.

We later found out that it was due to the transients in the power while screwing or unscrewing the power to the board live. The POR circuitry of the AT91 processor is not capable of rescuing the processor from hangs. What we did was to connect the power good of the last power rail to come up to NRST pin of the processor. This saves us from using external RTC as well as loosing internal RTC data.

The POWERGOOD signal of the last fired regulator holds the reset low till all the power supply lines are stable. This was the cheapest work-around as well as the smartest.

PS:The internal POR circuitry is supposed to handle this case. The POR should de assert the RST only after all the power supply rails feeding the processor are stable and transient free. Hope Atmel will take care of this in a revision.


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