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Date: Thu, 23 Apr 2015 18:29:09 +0300 From: "Grygorii.Strashko@...aro.org" <grygorii.strashko@...aro.org> To: Nishanth Menon <nm@...com>, "Grygorii.Strashko@...aro.org" <grygorii.strashko@...aro.org>, Alexandre Belloni <alexandre.belloni@...e-electrons.com>, Alessandro Zummo <a.zummo@...ertech.it> CC: linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org, rtc-linux@...glegroups.com Subject: Re: [PATCH V2] drivers/rtc/rtc-ds1307.c: Enable the mcp794xx alarm after programming time On 04/23/2015 04:11 PM, Nishanth Menon wrote: > On 04/23/2015 05:17 AM, Grygorii.Strashko@...aro.org wrote: >> On 04/23/2015 03:00 AM, Nishanth Menon wrote: >>> On 04/22/2015 08:26 AM, Grygorii.Strashko@...aro.org wrote: >>>> Hi, >>>> >>>> On 04/21/2015 03:51 AM, Nishanth Menon wrote: >>>>> Alarm interrupt enable register is at offset 0x7, while the time >>>>> registers for the alarm follow that. When we program Alarm interrupt >>>>> enable prior to programming the time, it is possible that previous >>>>> time value could be close or match at the time of alarm enable >>>>> resulting in interrupt trigger which is unexpected (and does not match >>>>> the time we expect it to trigger). >>>>> >>>>> To prevent this scenario from occuring, program the ALM0_EN bit only >>>>> after the alarm time is appropriately programmed. >>>>> >>>>> Ofcourse, I2C programming is non-atomic, so there are loopholes where >>>>> the interrupt wont trigger if the time requested is in the past at >>>>> the time of programming the ALM0_EN bit. However, we will not have >>>>> unexpected interrupts while the time is programmed after the interrupt >>>>> are enabled. >>>> >>>> I think it will be nice if you will mention that you going to follow >>>> vendor recommendations - AN1491 Configuring the MCP794XX RTCC Family >>>> http://ww1.microchip.com/downloads/en/AppNotes/01491A.pdf >>>> ;) >>>> "Also, it is recommended that the alarm registers be loaded >>>> before the alarm is enabled." >>>> >>> >>> Hmm... i did not know that existed, thanks for digging it up.. that >>> teaches me to look for docs before putting a scope/LA on the board >>> (not that I regret doing that)... That said, reading the app note, I >>> kind of realized: >>> a) that playing with ST bit for programming time is not done, but >>> then, that implies that oscillator will have to be restarted (upto a >>> few seconds for certain crystals).. but that said, it does not seem >>> mandatory or seem to (yet seen) functional issues... >>> >>> b) We dont have flexibility yet to describe if we do indeed have a >>> backup battery or not - VBATEN should be set only if we have a backup >>> battery on the platform :( - on some it might even be optional thanks >>> to certain compliance requirements of shipping boards internationally >>> and general "unlike" of lithium ion in cargo hold.. >>> >>> c) we dont have capability to control the alarm polarity in the driver >>> which, by the way, we probably should also control OUT polarity (when >>> ALARM is not asserted).. >>> >>> d) we dont have support for external 32k oscillator(X1 only) instead >>> of assuming we always have a 32k crystal(X1 and X2)... >>> >>> Ugghhh... more cleaning up to do for the future.. >>> >>> that said, the sequence it does recommend (in page 4): >>> The following steps show how the Alarm 0 is config- >>> ured. Alarm 1 can be configured in the same manner. >>> 1. Write 0x23 to the Alarm0 Seconds register >>> [0x0A]. >>> 2. Write 0x47 to the Alarm0 Minutes register >>> [0x0B]. >>> 3. Write 0x71 to the Alarm0 Hours register [0x0C] >>> – 11 hours in 12-hour format. >>> 4. Write 0x72 to the Alarm0 Day register [0x0D] – >>> Tuesday + Alarm Polarity Low + Match on all. >>> The Alarm0 Interrupt Flag is also cleared. >>> 5. Write 0x14 to the Alarm0 Date register [0x0E]. >>> 6. Write 0x08 to the Alarm0 Month register [0x0F]. >>> With all the Alarm0 registers set we can now activate >>> the Alarm0 on the Control register. >>> 7. Write 0x10 to the Control register [0x07] – >>> Alarm0 enabled no CLKOUT, Alarm1 disabled >>> >>> before this patch we do ( http://pastebin.ubuntu.com/10863880/) >>> CONTROL r[7] = 0x90 (OUT=1, ALM0EN=1) >>> OSCTRIM r[8] = 0x00 >>> EEUNLOCK r[9] = 0x00 >>> ALM0SEC r[A] = 0x01 >>> ALM0MIN r[B] = 0x45 >>> ALM0HOUR r[C] = 0x23 >>> ALM0WKDAY r[D] = 0x75 <-ALMOIF is cleared >>> ALM0DATE r[E] = 0x09 >>> ALM0MTH r[F] = 0x04 >>> RSRVED r[10] = 0x01 >>> >>> with this patch, we do: >>> burst( CONTROL r[7] = 0x80 (OUT=1) >>> OSCTRIM r[8] = 0x00 >>> EEUNLOCK r[9] = 0x00 >>> ALM0SEC r[A] = 0x01 >>> ALM0MIN r[B] = 0x45 >>> ALM0HOUR r[C] = 0x23 >>> ALM0WKDAY r[D] = 0x75 <-ALMOIF is cleared >>> ALM0DATE r[E] = 0x09 >>> ALM0MTH r[F] = 0x04 >>> RSRVED r[10] = 0x01 >>> ) >>> CONTROL r[7] = 0x90 (OUT=1, ALM0EN=1) >>> >>> Which is slightly unoptimal way of what the app note recommends. - as >>> I mentioned earlier in this thread, I will try and do optimizations in >>> a later patch. >>> >>> Given that Andrew had picked up this patch, I dont see a reason to >>> respin this yet. but will include the app note for future patches - >>> thanks for pointing it out to me. >> >> ^^ Up to you. Np, Always yours! > > Considering the narrow focus of the current patch (which does fix an > issue that it attempts to), can I get an Ack? > > Reviewed-by: Grygorii Strashko <grygorii.strashko@...aro.org> -- regards, -grygorii -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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