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RTC issue?
Added by Kevin Robertson over 11 years ago
Hi,
We are seeing an issue with the L138 RTC not running on our custom board - using hwclock we never see the time change.
I did some investigation and it looks like the SET32COUNTER bit in the RTC CTRL REG is always set after boot: I added some debug prints to omap_rtc.c, omap_rtc_probe(). I modified omap_rtc_probe() to reset this bit and the RTC starts operating as expected.
My issue is that I can't see where this bit would be set? Looking at omap_L138 Technical manual this bit should reset to 0.
I tested the same L138 module on a Critical Industrial IO Base Board and this bit isn't set - hwclock operates as expected.
The only difference(I can think of) is that the Critical has a Controlled POR using U104 where as our custom board doesn't. I did try an experiment holding our reset button while powering on to simulate Industrial IO but didn't see any change in behavior.
Thanks
Kevin
Replies (3)
RE: RTC issue? - Added by Michael Williamson over 11 years ago
Have you measured the Battery Backup voltage on your board through a power cycle? If the backup voltage drops below the required threshold, I think the RTC CTRL register resets to a disabled state.
-Mike
RE: RTC issue? - Added by Kevin Robertson over 11 years ago
I've check with the HW designer and he thinks it should be OK, see his info below
"The 3V_RTC pin of the L138 Module is at 2.7V when powered off. The design worst case should be 2.6V.
This is greater than the 2.5V that I believe is required to ensure that there is sufficient headroom for the 1V2 LDO on the board that powers the RTC circuitry."
Thanks
Kevin
RE: RTC issue? - Added by Michael Williamson over 11 years ago
Hi Kevin,
Would you be willing (offline) to share your schematics so that we might take a peek?
It's not obvious why you are having issues here.
-Mike
