PSoC™ 4 Forum Discussions

I am playing with the example project, RTC_P4_WDT_Example01, using the CY8CKIT-042-BLE-A Pioneer Kit.  The RTC component (version 1.30) does not handle the DST flag in the status register of struct RTC_DATE_TIME.

void RTC_Update(void)
{
    //  [skip a bit...]

    #if(0u != RTC_INITIAL_DST_STATUS)
        if(RTC_unixTime == RTC_unixTimeDstStart)
        {
            RTC_dstStatus = 1u;
            RTC_dstTimeOffset = RTC_SECONDS_PER_HOUR;
        }

        if(RTC_unixTime == (RTC_unixTimeDstStop - RTC_dstTimeOffset))
        {
            RTC_dstStatus = 0u;
            RTC_dstTimeOffset = 0u;
            RTC_unixTimeDstStart = RTC_GetDstUnixTime(&RTC_dstStartTime);
            RTC_unixTimeDstStop  = RTC_GetDstUnixTime(&RTC_dstStopTime);
        }
    #endif /* (0u != RTC_INITIAL_DST_STATUS) */
//  [.... more .... ]

Note that RTC_dstStatus is set and cleared correctly, but this information never makes it into the status register. 

In contrast, here is the code that immediately follows this.  It handles the alarm status:

    //  [..... continued ....  ] 
   #if(0u != RTC_INITIAL_ALARM_STATUS)
        if((RTC_unixTime + RTC_dstTimeOffset) == RTC_unixTimeAlarm)
        {
            RTC_currentTimeDate.status |= (1uL << RTC_STATUS_ALARM_OFFSET);
            RTC_alarmCurStatus = RTC_alarmCfgMask;

            RTC_unixTimeAlarm = 
            RTC_GetNexAlarmTime(RTC_unixTime + RTC_dstTimeOffset,(uint8)RTC_alarmCfgMask);

            /* Call callback function only after new alarm time is obtained.
            * Cypress ticket #264756
            */
            if (RTC_alarmCallbackPtr != NULL)
            {
                RTC_alarmCallbackPtr();
            }
        }
    #endif/* (0u != RTC_INITIAL_ALARM_STATUS) */

Right there near the top, there's a line that modifies RTC_currentTimeDate.status.  This read-modify-write indicates the correct alarm status, but this step is missing for DST status.

To investigate this, I added a few lines of code to UpdateTimeIsrHandler() to get and print the current RTC_DATE_TIME.status .  The expected behaviour is that the status flag will change when 3:00 becomes 4:00.  It does not.

You might even think that RTC_ReadStatus() would help.  Its description says that it "Reads the Status software register, which has flags for DST (DST), Leap Year (LY), AM/PM (AM_PM)."  But it does not do this.  Instead, it modifies the Status register with the correct flags for LY and AM_PM, and then returns the modified status.  Note that if RTC_ReadStatus() is never called, then these bits are never modified.  It seems weird that an API with the name "Read" is the only way to modify the status register.  The description of RTC_ReadStatus() suggests that we use RTC_GetDateAndTime() instead, and then access the status register directly.  However, if we do this, these bits will always be zero. 

Even knowing this weird behaviour does not help with DST, because RTC_ReadStatus() does not modify status register with the correct value of the DST status flag, so even calling RTC_ReadStatus() does not return the correct DST status.

How does anyone know whether the current time is DST?  None of the APIs give you this information, and the DST flag in the status register doesn't do anything.  The only way to know if DST applies to the current time is to invoke the global flag uint8 RTC_dstStatus.  In the component datasheet, DST is mentioned 109 times.  RTC_dstStatus is given just  these five words by way of explanation: "The DST start/stop status".  That's a bit too economical.

This weirdness in how the RTC component handles the status register could explain problems that other users have encountered, such as the failure to update status described in this post.