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Real Time Clock on STM32F4

Started by wanchp, Feb 28 2013 09:22 AM

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5 replies to this topic

#1 wanchp

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Posted 28 February 2013 - 09:22 AM

Since the hardware resource of STM32F4 includes calendar RTC with a dedicated power pin for that. I'll be nice if the next netduino supports on-chip RTC.

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#2 Chris Walker

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Posted 01 March 2013 - 12:13 AM

Hi wanchp, We're hoping that Arduino uses the "empty pin" on the new R3 pinout as a VBAT pin. The reason we don't expose the RTC is because there's no power pin suitable for it on the Arduino pinout. It would also increase the price of the boards a little bit. We considered using the now-empty "AREF" pin as a "VBAT" pin instead...but then you'd risk electrocuting your board simply by plugging in an Arduino shield which feeds a 5V AREF to that pin. Chris

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#3 wanchp

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Posted 03 March 2013 - 03:15 PM

Hi Chris,

On the current Netduino+2, VBAT pin of STM32F4 is tied up with the VDD. Though nothing can prevent you from developing on-chip RTC drivers. You may start with ST's AN3371, RTC firmware driver API.

On the next Netduino+(3?), you may add a 3V button battery or a supercap to keep on the time. There is no need to increase short-circuit risk.

Wanchp

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#4 Chris Walker

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Posted 05 March 2013 - 07:37 AM

Hi Wanchp,

On the current Netduino+2, VBAT pin of STM32F4 is tied up with the VDD. Though nothing can prevent you from developing on-chip RTC drivers. You may start with ST's AN3371, RTC firmware driver API.

If you wanted to play around with the low-level RTC code you can. I'm not sure how accurate the time would be though--without an external 32.768KHz crystal. It might be good for wakeup events and such though.

On the next Netduino+(3?), you may add a 3V button battery or a supercap to keep on the time. There is no need to increase short-circuit risk.

That would be cool. There may not be enough room on Netduino Plus...but if there's enough demand, we could create a special Netduino with onboard supercap or battery. Great feedback!

Chris

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#5 neslekkim

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Posted 05 March 2013 - 07:56 AM

an place to solder pins would help also I guess, it would be up to the user to add them, maybe one need an solderbridge if not using them, but still. (Teensy does similar things)

--
Asbj�rn

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#6 wanchp

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Posted 08 March 2013 - 04:46 AM

Hi Wanchp,If you wanted to play around with the low-level RTC code you can. I'm not sure how accurate the time would be though--without an external 32.768KHz crystal. It might be good for wakeup events and such though.That would be cool. There may not be enough room on Netduino Plus...but if there's enough demand, we could create a special Netduino with onboard supercap or battery. Great feedback! Chris

You are right, the time running on the internal rc clock source is not accurate. However, if one connect to the net from time to time, the precise time can be read from an ntp server.

Neslekkim is right, you can just provide a few solder pads/poles for 32kHz OSC and a supercap but pins for OSC32-IN and OSC32-OUT are now occupied.

Chris, I am a novice here, if I really want to play with low level hardware like RTC, do I have to customize the .net micro framework or your netduino firmware or both? Can you point out a good starting point?