I want to use RTT as a RTC on board AT91SAM9260-EK. Somebody has experience with this ? It can explain it ?

Thank you.

Think there are bugs in the Boot ROM, so not right now.

Hi there

I've started to look into using the RTT to maintain a clock calender also. The biggest problem I discovered so far is that the counter (the Value register), along with the other RTT registers, are reset on processor reset or power-up. If it wasn't for this issue, I think I've got a scheme that would work. The RTT Value register would have a running count of elapsed time (delta seconds), and one of the battery-backed, general purpose registers would hold a base time (base seconds). So delta + base = current seconds since epoch.

Regards

BTW the maxim.org site mentions that a SAM9 RTC driver is "in development".

Looks like Atmel is aware of this problem:

44.2.1 Boot ROM
44.2.1.1 Problem with RTT
The Real-time Timer is reset by the BootROM after each power up. This prevents using the RTT as a backed up real-time clock.

Is this the same issue for the AT91SAM9261 as well ?

Hi there

Have you check the Errata chapter of the Atmel doc for the at91sam921?
Have you tried checking what the RTT Value register is after a reset (try using the md command of U-Boot)?

Regards

I'm using the AT91SAM9261, all the four RTT registers remains after a reboot or power off if you feed the board with a battery.

Regards.