On 04/23/2015 03:00 AM, Nishanth Menon wrote: > On 04/22/2015 08:26 AM, Grygorii.Strashko@xxxxxxxxxx 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! >>> >>> Signed-off-by: Nishanth Menon <nm@xxxxxx> >>> --- >>> Changes in v2: >>> - minor typo fix in comments >>> - merged up code that I missed committing in >>> >>> V1: https://patchwork.kernel.org/patch/6245041/ >>> >>> drivers/rtc/rtc-ds1307.c | 12 ++++++------ >>> 1 file changed, 6 insertions(+), 6 deletions(-) >>> >>> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c >>> index 4ffabb322a9a..3cd4783375a5 100644 >>> --- a/drivers/rtc/rtc-ds1307.c >>> +++ b/drivers/rtc/rtc-ds1307.c >>> @@ -742,17 +742,17 @@ static int mcp794xx_set_alarm(struct device *dev, struct rtc_wkalrm *t) >>> regs[6] &= ~MCP794XX_BIT_ALMX_IF; >>> /* Set alarm match: second, minute, hour, day, date, month. */ >>> regs[6] |= MCP794XX_MSK_ALMX_MATCH; >>> - >>> - if (t->enabled) >>> - regs[0] |= MCP794XX_BIT_ALM0_EN; >>> - else >>> - regs[0] &= ~MCP794XX_BIT_ALM0_EN; >>> + /* Disable interrupt. We will not enable until completely programmed */ >>> + regs[0] &= ~MCP794XX_BIT_ALM0_EN; >>> >>> ret = ds1307->write_block_data(client, MCP794XX_REG_CONTROL, 10, regs); >>> if (ret < 0) >>> return ret; >>> >>> - return 0; >>> + if (!t->enabled) >>> + return 0; >>> + regs[0] |= MCP794XX_BIT_ALM0_EN; >>> + return i2c_smbus_write_byte_data(client, MCP794XX_REG_CONTROL, regs[0]); >> >> So, It seems, that right sequence should be: >> - disable alarmX >> - read alarmX regs >> - configure alarmX regs >> - load alarmX regs >> - enable alarmX > Not exactly.... see above. we can optimize this for a better sequence > as follows - since there are already un-necessary reads being > performed. probably just a couple of reads might be > sufficient..(ALM0WKDAY has some control bits as well.. Ugggh.. > anyways..)... > > > Will have to think more about optimizing more later. Also I've done some fast investigation and I found that ~half of RTC drivers disable ALM IRQ before start accessing Alarm regs (twl-rtc.c) while another half don't do that :) (just FYI) > >> >> More over, looks like, alarm/alarm IRQ should be enabled/disabled separately from set_alarm/RTC_ALM_SET >> by RTC_AIE_ON, RTC_AIE_OFF. Should it? > -- regards, -grygorii -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
